R 21_Time Sharing_System_Reference_Oct68 21 Time Sharing System Reference Oct68

R-21_Time-Sharing_System_Reference_Oct68 R-21_Time-Sharing_System_Reference_Oct68

User Manual: R-21_Time-Sharing_System_Reference_Oct68

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REFERENCE

MANUAL

TJME-

SHARING

SYSTDi

L.

Peter

Deutsch

Larry

Durham

Butler

W.

Lampson

t'fn1versity

of

California,

Berkeley

Document No.

R-2l

Revised October 22,

1968

Office

of

Secretary

of

Defense

Advanced Research

Projects

Agency

Washington,

D.

C.

20325

1.0

Introductory.

.

2.0

The

Scheduler.

.

PAC

TABLE

..

TABLE

OF

CONTENTS

. . . .

Phantom

user

queue

entry

••

3.0 Forks and Jobs . •

3.1

Creation

of

Forks •

Hierarchy

of

Processes

• •

3.2

Memory

Acquisition.

• •

3.3

Panic

Conditions.

•

. . . . . .

3.4 Jobs

••.••••

Job Tables •

4.0 Program

Interrupts

• • . . .

5.0

The

Swapper and

Memory

Allocation

••

6.0 Miscellaneous

Featur~s

.

7.0

Teletype

Input-Output.

• • ·

TELETYPE

SYSTEM

POINTERS

TElETYPE

TABLE

•

TELETYPE

BUFFERS

•

. . .

8.0

Drum

and

Buffer

Organization;

Devices.

8.1

File

Storage

on

the

Drum.

• . • • •

8.2

File

Buffers

•.•.•.

8.3

Devices.

• • • • •

Layout

of

a

File

Buffer.

Forma~

of

an Index Block • .

Device Indexed Tables • • • • •

9.0

Sequential

Files

. . . • • .

9.1

Sequential

Drum

Files

.

9.2 Other

Sequential

Files.

9.3

File

Control

Blocks

.•

9.4 Permanently

Open

Files.

10.0

Random

Drum

Files

•.••.

10.1

Direct

Drum

Access

11.0

Subroutine

Files

. • • •

.

".

1-1

2-1

2A

2B

3-1

3-1

3A

3-4

3-5

3-7

3B

4-1

5-1

6-1

7-1

7A

7B

7C

8-1

8-1

8-2

8-3

8A

8A

8B

9-1

9-1

9-7

9-11

9-11

10-1

10-3

11-1

12.0

File

Naming

System . . . • . •

12-1

13·0

14.0

12.1

File

Naming. . . . • • • .

12-2

12.2

Accessing

Other

Users'

Files,

Special

Groups

12-4

12.3

Pseudonyms.

. . . . • • . • • . . . . .

12-5

12.4

Doing I/O

to

Files,

File

Numbers

12-5

12.5

Opening

Input

Files

•.

TAPE

or

PERMANENT

FILES.

SCRATCH

FII~S.

.

BUILT-IN

FILES

.

SPECIAL

GROUPS

.

PSEUDONYMS.

. .

FILE

DIRECTORY

DESCRIPTION

USER

DIRECTORY

DESCRIPTION

.

.

12.6

Opening

Output

Files

•

12-6

12A-l

12A-l

12A-1

12A-2

12A-2

l2A-3

l2A-4

12-8

12.7

Miscellaneous

File

Operations.

.

12-10

12.8

Opening

Scratch

Files.

. . . • .

.•

. .

12-12

12.9

Format

of

the

File

Directory,

Some

Implementation

Details

. . .

~

. . . . • . . . .

12-13

12.10

Miscellaneous

Services

...

Miscellaneous

Executive

Features

.

StrinG

Processing

System .

14.1

Strine

Pointer

Load

and

Store

Operations.

14.2

String

Read and

Write

Operations

•....•.

14.3

String

Compare

Operations

14.4

String

Input/Output

.••.•

14.5

Hash Table

J~okup

Instructions

.

15.0

Floating

Point

Instructions

••••.••.

15.1

Floating

Point

Representation

•.

15.2

Floating

Point

Arithmetic

•.•

12-14

13-1

14-1

14-1

14-1

14-3

14-3

14-4

15-1

15-1

15-2

15-3

15-4

A-I

B-1

15.3

Input/Output

Formats and Conventions

15.4

Input/Output

Operations..

•

••.

BRS

TABLE.

SYSTEM

PROGRAMMED

OPERATORS.

.

1-1

1.0

Introductory

The

Berkeley

Time-Sharing System

is

divided

into

three

major

parts:

The

monitor,

the

executive,

and

the

subsystems.

Only

the

first

two

of

these

are

discussed

in

detail

in

this

manual.

The

manual

attempts

to

describe

exhaustively

all

the

features

of

the

monitor

and

in

addition

to

give

a number

of

implementation

details.

It

also

describes

those

features

of

the

executive

which

can be invoked by a program.

We

use

the

word

monitor

to

refer

to

that

portion

of

the

system

which

is

concerned

with

scheduling,

input-output,

interrupt

processing,

memory

allocation

and swapping, and

the

control

of

active

programs.

The

executive,

on

the

other

hand,

is

concerned

with

the

control

of

the

directory

of

symbolic

file

names and

backup

storage

for

these

files,

and

various

miscellaneous

matters.

Other

parts

of

the

executive

handle

the

command

language

by

which

the

user

controls

the

system fram

his

teletype,

the

identification

of

users

and

specification

of

the

limits

of

their

access

to

the

system. These

subjects

are

discussed

in

the

executive

reference

manual, Document R-22.

The

next

ten

sections

of

this

manual

discuss

various

features

of

the

monitor.

The

remaining

sections

deal

with

the

executive.

2-1

2.0

The

Scheduler

The

primary

entities

with

which

the

time-sharing

system

is

concerned

are

called

active

programs.

Each

active

program

is

an

abstract

object

capable

of

executing

machine

instructions.

At

least

one

active

program

is

associated

with

each

active

user,

but

a

user

may

have

many

programs,

each

computing

independently

under

his

control.

An

active

program

is

defined

by

its

entry

in

the

program

active

table

(PAC

table

or

PACT).

This

table

contains

all

of

the

information

required

to

specify

the

instantaneous

state

of

the

extended

computer which

the

user

is

programming,

except

for

that

contained

in

the

user's

memory

or

in

the

system's

permanent

tables.

The

structure

of' a

PACT

entry

is

displayed

on

the

following

page,

together

with

brief

notes

about

the

significance

of

the

various

items.

These

matters

will

be

explained

in

more

detail

in

the

following

few

sections.

It

will

be

observed

that

PACT

contains

locations

for

saving

the

program

counter

and

the

contents

of

the

active

A,

B and X

registers.

It

also

contains

two

pseudo-relabeling

registers

for

the

user.

A

third

one,

which

specifies

the

monitor

map,

is

kept

in

the

job

tables.

The

matter

of

pseudo-relabeling

is

discussed

in

detail

in

Section

5.

There

is

a word

called

PTEST

which

determines

the

conditions

under

which

the

program

should

be

reactivated

if

it

is

not

currently

running.

The

panic

table

address

in

PTAB

and

the

three

pointers

called

PFORK,

PDOWN

and

PPAR

are

discussed

in

Section

3 on

forks.

The word

called

PTAB

contains

in

bits

2

through

8

the

number

of

the

job

to

which

this

program

belongs.

The

top

of

PQU

contains

information

about

the

amount

of

time

for

which

the

program

is

allowed

to

compute

before

it

is

dismissed.

A

job

table

called

QUR

counts

the

number

of

clock

cycles

remaining

before

the

program

is

dismissed,

and

three

bits

of

QUTAB

point

to

a

table

which

specifies

the

length

of

time

which

the

program

should

be

allowed

to

run

when

it

is

activated.

All

times

1n

the

discussion

are

measured

in

periods

of

the

60-cycle

computer

clock.

PNEXT

PL

PA

PB

PX

RLl

RL2

PPTR

prEST

PQU

PTAB

PIM

2A

PAC

TABLE

next

queue

or

next

program

in

queue

U 0

~

file

if

of

8

(p)

M 0 V

subroutine

0

saved

file

saved

(A)

saved

(B)

saved

(X)

l'i.rst

pseudo-relabeling

register

sec()nd

pseudo-relabeling

register

0

11

12

pj6w~r

PF¢RK

13

. . 8

000

I

~ctl~a~lon

0

~o

test

word

address,

or

other

~:ondltlon

relevant

parameter

E ~2 8 9

11

12

X B

Q,N

GlJrAB

PPAR

2 8

0-0

L

M 0

Job

number 0

panic

table

address

~--

M T N

~I

rEM

T w T

UM

=

user

mode

(l)

or

system

OV

=

overflow

pn¢WN

=

PACT

address

of

lower

fork

(if

any)

PFPRK

=

PACT

address

of

upper

fork

(if

any)

FPAR

:=

PACT

address

of

pa.rallel

fork

(ends

with

0)

QUTAB

=

address

of

word

in

table

indicating

quantum

lengths

EX

=

executive

type

program

EB

=

exec

BRS

I

I

j

1

I

r

I

I

I

I

23

I

231

I

23

1

23

23

Q~

=

saved

queue

number

i~

on

QOV

TW

=

waiting

for

termination

rEM

=

interrupt

enabled

mask

1M

=

local

memory

MT

=

add

no

memory

NT

=

non-terminable

EM

=

destroy

memory when

fork

is

terminated

2-2

A program

is

a.lloT..red

to

run

for

a

fixed

period

of

time,

after

which

it

is

dismissed

if

any

other

programs

are

ready

to

run.

This

time

is

called

a

long

quanttun.

It

may

be

different

for

different

programs.

In

fact,

the

size

of

the

long

quantum

is

determined

by

the

entry

in

QTAB

which

is

pointed

to

by

the

program's

QUTAB

in

PACT.

When

a program

is

activated,

it

is

first

allowed

to

run

for

a

short

quantum. During

this

time

it

cannot

be

dismissed

except

by

its

own

request.

The

length

of

the

short

quantum

is

tentatively

going

to

be

the

same

for

all

users.

It

is

put

into

a word

called

TlME;

the

long

quantum

is

also

put

into

a word

called

TTlME

at

this

time.

Both

are

decremented

at

every

clock

cycle.

When

TIME goes

negative,

a word

called

ACTR

is

checked

to

determine

whether

any program which

is

dismissed

for

I/O

can

be

run.

If

not,

the

program

is

allowed

to

continue.

At

each

subsequent

clock

cycle

the

program

may

be

dismissed

if

any programs

dismissed

for

I/O

are

ready

to

run.

It

may

also

be

dismissed

when

the

long

quantum

is

exhausted

if·

any

other

programs

are

waiting

to

run.

In

either

case

it

is

said

to.

be

dismissed

for

quantum

overflow.

If

ACTR

indicates

that

another

program

dismissed

for

I/O

is

ready

to

run

at

the

end

of

the

short

quantum,

the

program

is

also

dismissed

for

quantum

overflow.

In

order

to

allow

an

efficient

~plementation

of

this

scheme,

ACTR

is

incremented

by

every

interrupt

routine

which

takes

action

allowing

a program which

is

waiting

for

I/O

to

run.

ACTR

is

set

to

-1

when

a program

is

activated.

When

a program

is

dismissed

for

I/O,

TT:mE

is

put

into

QUR.

When

the

program

is

reactivated,

TTIME

is

set

from

QUR.

TIME

is

reset

to

the

full

short

quantum. That

is,

the

long

quantum

is

allowed

to

run

down

while

a program computes,

regardless

of

whether

it

has

to

wait

for

I/O

between compute,tions. On

the

other

hand, a program

is

always

given

a

full

short

quantum.

If

a program

is

dismissed

for

quantum

overflow,

it

is

given

a

new

long

quantum

when

it

is

reactivated.

There

are

two

operations

available

to

the

user

which

are

connected

with

the

quantum

overflow

machinery.

BRS

45

causes

the

user

to

be

dismissed

as

though he had overflowed

his

quantum.

BRS

57

guarantees

to

the

user

upon

return

at

least

16

msec

of

2-3

uninterr~pted

computation.

This

feature

is

implemented

by

dismissing

the

user

if

less

tha.n 16

;TI~;ec

remain

in

his

quantum.

Ordinarily,

the

code which

is

being

executed

at

any

particular

instant

is

that

belonging

to

the

program which

is

currently

active.

This

situation

may

be

disturbed,

however, by

the

occurrence

of

interrupts

from I/O

devices.

These

interrupts

cause

the

computer

to

enter

system

mode

and

are

processed

entirely

independently

of

the

currently

running

program. They

never

take

direct

action

to

disturb

the

running

of

this

program,

although

they

may

set

up

conditions

in

memory

which

will

cause

some

other

program

to

be

activated

when

the

presently

running

one

is

dismissed.

Interrupt

routines

always

run

in

system mode.

Other

code which

may

be

running

which

may

not

belong

to

the

program

currently

active

is

the

code

of

system

programmed

operators

or

BRS

routines.

These

routines

s.re

not

re-entrant

and

therefore

should

not

be

dismissed

by

the

clock.

To

ensure

that

they

will

not

be,

the

convention

is

established

that

the

clock

will

not

dismiss

a program

running

in

system mode.

In

order

to

~larantee

that

a·user

program

will

not

monopolize

the

machine by

executing

a

large

number

of

SYSPOPs,

the

user

mode

trap

is

turned

on

when

the

clock

indicates

that

a program

is

to

be

dismissed.

The

trap

will

occur

and

cause

dismissal

as

soon

as

the

program

returns

to

user

mode.

The

PACT

word

called

PTEST

contains

the

activation

condition

for

a

currently

inactive

program.

The

condition

for

activation

is

contained

in

the

6 opcode

bits

of

this

word,

while

the

address

field

normally

contains

the

absolute

address

of

a word

to

be

tested

for

the

~pecified

condition.

(ThiS

word

is

usually

something

like

TTYBRK

for

a

user's

teletype~

It

is

possible,

however,

for

the

address

to

contain

a

time

count,

in

the

case

where

the

activation

condition

is

that

a

certain

amount

of

time

should

elapse.

It

is

also

possible

for

the

address

to

hold

a mask

indicating

which program

interrupt

has

occurred.

The

following

activation

conditions

are

possible:

o

Word

greater

than

0

I

Word

less

than

or

equal

to

0

2

Word

greater

than

or

equal

to

0

3

Word

less

than

or

equal

to

teletype

early

warning

4

Special

test.

The

address

points

to

a

special

activation

test

routine.

5

Interrupt

occurred.

The

address

contains

the

number

of

the

interrupt

which

occurred.

2-4

a

dead

1

running

2

BRS

31

7

Special:

address

= 3

BRS

106

4

executive

BRS

5

BRS

109

11

Bit

1

of

word

is

1

(buffer

ready)

12

Word

less

than

zero

An

executive

program

can

dismiss

itself

explicitly

by

putting

a queue

number

(0

to

3)

in

X and a

dismissal

condition

in

B and

executing

BRS

72.

The

address

of

a

dismissal

condition

must

be

absolute.

There

is

normally

one

running

program

in

the

system,

i.e.,

a program which

is

executing

instructions,

or

will

be

executing

instructions

after

the

currently

pending

interrupts

have

been

processed.

An

active

program

(i.e.

a

PACT

entry)

which

is

not

running

is

said

to

be

dismissed,

and

is

kept

track

of

in

one

of

two ways.

1)

If

it

has

dismissed

itself

with

BRS

31,

106

or

109

(cf.

section

5)

it

is

said

to

be

in

limbo and

is

pointed

to

only

by

the

PFORK,

PDOWN,

and

PPAR

of

the

neighboring

programs

in

the

fork

structure.

2)

If

it

has

been

dismissed

for

any

other

reason,

it

is

on one

of

the

scheduler

queues.

There

are

four

queues

of

dismissed

programs.

In

order,

they

are:

QTI programs

dismissed

for

teletype

inp

1

1t/output

QIO

programs

dismissed

for

other

I/O

QSQ

programs

dismissed

for

exceeding

their

short

quanta

QQE

programs

diSmissed

for

exceeding

their

quanta.

Programs

within

the

queues

are

chained

together

in

PNEXT,

and

PNEXT

for

the

last

program

in

each

queue

points

to

the

beginning

of

the

next

queue.

Whenever

it

is

time

to

activate

a new program,

the

old

program

is

put

on

the

~

of

the

appropriate

queue.

The

scheduler

then

begins

at

QTI

and

scans

through

the

queue

structure

looking

for

a program whose

activation

condition

is

satisfied.

When

one

is

found,

it

is

removed from

the

queue

2-5

structure

antI

t;.~l";~C'(J

(~"ICl'

tc

tJ}C s",rap:pcr

to

be

read

in

and

run.

If

there

are

no

prograr:_s ,'Thich

ca.!,

be

act:i

vated

the

scheduler

simply

cont

inues

scanninG

the

queue

strl._:t~ture.

Programs

reactivated

for

various

r.easons

having

to

do

with

forks

(interrupts,

rubouts,

panics)

are

put

onto

QIO

with

an immediate

activation

condition.

They

therefore

take

priority

over

all

progrfu~s

dismissed

for

quantum

overflow.

There

is

a

permanent

entry

on

the

-teletype

queue

for

an

entity

called

the

phantom

user.

The

activation

condition

for

this

entry

is

a

type

4

condition

which

tests

for

two

possibilities:

a)

the

cell

PUCTR

is

non-zero

b )

three

seconds

have

elapsed

since

the

last

activation

of

the

phantom

user

for

this

condition.

\'lhen

the

phantom

user

is

act

i

vated

by

(b)

,

it

runs

around

the

system

checkinF~

that

everything

is

functioning

properly.

In

particular,

it

checks

that

the

W-buffer

has

not

been

waiting

for

an

interrupt

for

an

unusual

length

of

time,

and

that

all

teletype

output

is

pItteeding

normally.

Details

of

this

procedure

are

described

in

sections

9 and 7.

If

the

phrultom

user

is

activated

by

(a),

it

runs

down

the

phantom

user

queue

looking

for

things

to

do.

A phantom

user

queue

entry

is

drawn on

page

2B;

it

is

essentially

a

very

abbreviated

PAC

table

entry.

Such an

entry

is

made

when

the

system

has

some

activity

which

it

wants

to

carry

out

more

or

less

independently

of

any

user

PAC

table

entry:

testa

for

tape

ready

(on

rewind)

and

card

reader

ready,

and

processing

of

rubouts

(an

interrupt

routine

kind

of

activity,

but

too

time-consuming).

The

second

word

of

the

entry

is

the

activation

condition.

PUCTR

contains

the

number

of

entries

on

the

phantom

user

queue.

2B

Pointer

to

next

entry

p 5 9

23

test

number

routine

address

p

11

12

for

23

PACPrR

for

user

parameter

routine

Phantom

user

queue

entry

3-1

3.0

Forks

and

Jobs

3.1

Creation

of

Forks

A program

m~v

create

new,

dependent,

entries

in

the

PAC

table

by

executing

BRS

9·

This

BRS

takes

its

argument

in

the

A

register,

which

contains

the

address

of

a

panic

table,

a 7-word

table

with

the

following

format:

Program COlmter

A

register

B

register

X

register

First

relabelin~

register

Second

relabeling

re~ister

status

The

status

word

may

be:

-2

dismissed

for

input-output

-1

running

0

dismissed

on

rub

cut

or

BRS

10

1

dismissed

on

illegal

instruction

panic

2

dismissed

on

memory

panic

The

panic

table

-address

must

not

be

the

same

for

two

forks

of

the

same

program,

or

overlap

a

pru~e

boundary.

If

it

is,

BRS

9

is

illegal.

The

first

7

bits

of

the

A

register

have

the

following

significance:

o

make

fork

executive

if

current

program

is

executive

1

set

fork

relabeling

from

panic

table.

Otherwise

use

current

relabeling

2

propagate

rubout

assignment

to

fork

(see

ERS

90)

3

make

fork

fixed

memor.l..

It

is

not

allowed

to

obt~

":.in

any more

memory

than

it

is

started

with.

. )

.J'

1.

0

UP

l-

I-

DOHl'J·

~

)

ACROSS

-:--

.

J

1-

1-

I.~.,....

1

t-

O

1,

"r

)

b

::-----------.---

..

-

...

-

..

--,

~

C)

o

8.

~

---

c

o

Hierarchy

of

Processes

5 .

6 .

10.

1

~

1

.-

6

0

I L

l

"...

')

I-

10

0

t.

6

~

r---

o

!-

(j

~.

. ,

I

r~l

9·

r'

l)

~

o

f'

V

"----

3-2

4.

make

fork

local

memory.

New

memory

will

be

assigned

to

it

independently

of

the

controlling

fork.

5.

make

fork

ephemeral

memory.

Memory

that

it

acquires

will

be

released

when

the

fork

terminates.

6.

set

interrupt

mask from

seventh

word

of

panic

table.

When

BRS

9

is

executed,

a

new

entry

in

the

PAC

table

is

created.

This

new

program

is

said

to

be a

fork

of

the

program

creating

it,

which

is

called

the

controlling

program.

The

fork

is

said

to

be

lower

in

the

hierarchy

of

forks

than

the

controlling

program. The

latter

may

itself

be a

fork

of

some

still

higher

program.

The

A,

B and X

registers

for

the

fork

are

set

up from

the

current

contents

of

the

p~~ic

table.

The

address

at

which

execution

of

the

fork

is

to

be

started

is

also

taken

from

the

panic

table.

The

relabeling

registers

are

set

up

either

from

the

current

contents

of

the

panic

table

or

from

the

relabeling

registers

of

the

currently

running

program.

An

executive

program

may

change

the

relabeling

as

it

pleases.

A

user

program

is

restricted

to

changing

relabeling

in

the

manner

permitted

by

BRS

44.

The

status

word

is

set

to

-1

by

BRS

9.

The

fork

structure

is

kept

tract

of

by

pointers

in

PACT.

For

each

program

PFORK

points

to

the

controlling

fork,

PDOWN

to

one

of

the

subsidiary

forks,

and

PPAR

to

a

fork

on

the

same

level.

All

the

subsidiary

forks

of

a

single

fork

are

chained

in

a

list.

A complex

situation

is

shown

on

the

previous

page.

The

arrows

indicate

the

various

pointers.

The

program

executing

a

BRS

9

continues

execution

after

the

instruction.

The

fork

established

by

the

BRS

9

begins

execution

at

the

location

specified

in

the

panic

table

and

continues

independently

until

it

is

terminated

by

a

panic

as

described

below.

It

is

connected

to

its

controlling

program

in

the

following

three

ways:

1)

The

controlling

program may examine

its

state

and

control

its

operation

with

the

following

six

instructions:

BRS

30

BRS

31

BRS

32

read.s

the

current

status

of

a

subsidiary

fork

into

the

panic

table.

It

does

not

influence

the

operation

of

the

fork

in

any way.

causes

the

controlling

program

to

be

dismissed

until

the

subsidiary

fork

causes

a

panic.

When

it

does,

the

controlling

program

is

reactivated

at

the

instruction

following

the

BRS

31, and

the

panic

table

contains

the

status

of

the

fork

on

its

dismissal.

The

status

is

also

put

into

x.

causes

a

subsidiary

fork

to

be

unGondi

tionally

terminated

and

its

status

to

be

read

into

the

panic

table.

All

of

these

instructions

require

the

panic

table

address

of

the

fork

in

A.

They

are

illegal

if

this

address

is

not

that

of

a

panic

table

for

some

fork.

ERS

31 and

BRS

32

return

the

status

word

in

the

X

register,

as

well

as

leaving

it

in

the

panic

table.

This

makes

it

convenient

to

do an

indexed

,jump

,.,i

th

the

contents

of

the

status

word.

BRS

31

returns

the

paniC

table

address

in

A.

BRS

106

BRS

107

BRS

loB

causes

the

controlling

program

to

be

dismissed

until

any

subsidiary

fork

causes

a

panic.

When

it

does,

the

controlling

program

is

reactivated

at

the

following

instruction

with

the

panic

table

address

in

A,

and

the

panic

table

contains

the

status

of

the

fork

at

its

dismissal.

causes

ERS

30

to

be

executed

for

all

subsidiary

forks.

causes

BRS

32

to

be

executed

for

all

subsidiary

forks.

3-4

2)

If

interrupt

3

is

armed

in

the

controlling

fork,

the

termination

of

any

subsidiary

fork

will

cause

that

interrupt

to

occur.

The

interrupt

takes

precedence

over

a

BRS

31.

If

the

interrupt

occurs

and

control

is

returned

to

a

BRS

31

after

processing

the

interrupt,

the

fork

will

be

dismissed

until

the

subsidiary

fork

specified

by

the

restored

(A)

terminates.

3)

The

forks

can

share

memory.

The

creating

fork

can,

as

already

indicated,

set

the

memory

of

the

subsidiary

fork

when

the

latter

is

started.

In

addition,

there

is

some

interaction

when

the

subsidiary

fork

attempts

to

acquire

memory.

3.2

Memory

Acquisition

If

the

fork

addresses

a

block

of

memory

which

is

not

aSSigned

to

it,

the

following

action

is

taken:

a

check

is

made

to

determine

whether

the

machine

size

specified

by

the

user

(cf

..

Document R-22)

has

been

exceeded.

If

so,

a

memory

panic

(see

below)

is

generated.

If

the

fork

is

fixed

memory, a

memory

panic

is

also

generated.

Otherwise

a

new

block

is

assigned

to

the

fork

so

that

the

illegal

address

becomes

legal.

For

a

local

memory

fork,

a

new

block

is

always

assigned.

Otherwise,

the

following

algorithm

is

used.

The

number,

n,

of

the

relabeling

byte

for

the

block

addressed

by

the

instruction

causing

the

memory

trap

is

determined.

A

scan

is

made upwards

through

the

fork

structure

to

(and

including)

the

first

local

memory

fork.

If

all

the

forks

encountered

during

this

scan

have

Rn

(the

Nth

relabeling

byte)

equal

to

0,

a new

entry

is

created

in

PMT

for

a new

block

of

user

memory.

The

address

of

this

entry

is

put

into

Rn

for

all

the

forks

encountered

during

the

scan.

If

a

fork

with

non-zero

Fin

is

encountered,

its

Rn

is

propagated

downward

to

all

the

forks

between

it

and

the

fork

causing

the

trap.

If

any

fixed

memory

fork

is

encolJ.ntered

before

a

non-zero

Rn

is

found,

a

memory

panic

occurs.

This

arr&"1gement

permits

a

fork

to

be

started

with

less

memor;!

than

its

controlling

fork

in

order

to

minimize

the

amount

or

drum swapping

required

during

its

execution.

If

the

fork

later

proves

to

require

more

memory,

it

can

be

reassi[~ed

the

memory

of

the

controlling

fork

in

a

natural

way.

It

is,

of

course,

possible

to

use

this

machinery

in

other

ways,

for

instance

to

permit

the

user

to

acqutre

more

than

16K

of

memory,

and

to

run

different

forks

with

non-overlapping

or

almost

non-overlapping

memory.

3.3

Panic

Conditions

The

three

kinds

of

panic

condition

which

may

ca.use a

fork

to

be

terminated

are

listed

in

the

description

of

the

status

word

above.

When

e~y

of

these

conditions

occurs,

the

PACT

entry

for

the

fork

being

terminated

is

returned

to

the

free

program

list.

The

status

of

the

fork

is

read

into

its

panic

table

in

the

control1int~

fork.

If

the

fork

being

terminated

has

a

subsidiary

fork,

it

too

is

terminated.

This

process

will

of

course

cause

the

termination

of

all

the

lower

forks

in

the

hierarchy.

The

pRnic

which

returns

a

status

word

of

zero

is

called

a

program

panic

and

may

be

caused

by

either

of

two

conditions:

A)

the

rubout

button

on

the

controlling

teletype

is

pushed.

This

terminates

some

fork

with

a

program

panic.

A

fork

may

declare

that

it

is

3-6

the

one

to

be

terminated

by

executing

BRS

90.

In

the

absence

of

such

a

declaration

the

highest

user

fork

is

terminated

..

~~en

a

fork

is

terminated

in

this

way

its

controlling

fork

becomes

the

one

to

be

terminated.

If

a

user-

fork

is

terminated

by

rubout

the

teletype

input

huffer

is

cleared.

If

the

controlling

fork

of

the

one

terminated

is

executive,

the

output

buffer

is

f.tlso

cleared..

If

the

fork

which sl1ou1d

be

terminated

by

rubout

has

armed

interrupt

1,

this

interrupt

will

occur

instead

of

a

termination.

The

teletype

buffers

will

not

be

af'fected.

If

there

is

only

one

fork

active,

control

goes

to

the

location

EXECP

in

the

executive.

This

consideration

is

of

no

concern

to

the

user.

Executive

programs

can

turn

the

rubout

button

off

with

BRS

46 and

turn

it

back

on

with

BRS

4'7.

A

rubout

occurring

in

the

meantime

will

be

stacked.

A

second

one

will

be

ignored.

A

program

which

is

running

with

rubout

turned

off

is

said

to

be

non-terminable

and

cannot

be

terminated

by

a

higher

fork.

BRS

26

skips

if

there

is

a

rubout

pending.

If

two

rubouts

occur

within

about

.12

second.s,

the

entire

fork

structure

will

be

cleared

and

the

job

left

executing

the

top

level

executive

fork.

This

device

permits

a

user

trapped

in

a

malfunctioning

lower

fork

to

escape.

Closely

spaced

rubouts

can

be

conveniently

generated

with

the

repeat

button

on

the

teletype.

B)

A

BRS

10

may

be

executed

in

the

lower

fork.

This

condition

can

be

distinguished

from a paniC

caused

by

the

rubout

button

only

by

the

fact

that

in

the

former

case

the

program

counter

in

the

panic

table

points

to

a word

containing

BRS

10.

As

an

extension

of

this

machinery,

there

is

one

way

in

which

several

forks

may

be

terminated

at

once

by

a

lower

fork.

This

may

be

done

by

BRS

73,

which

provides

a

count

in

the

A

register.

A

scan

is

made

upward

through

the

fork

structure,

decrementing

this

count

by

one

each

time

a

fork

is

passed.

When

the

count

goes

to

0,

the

scan

is

terminated

and

all

forks

passed

by

are

3-7

terminated.

If

an

executive

program

is

reached

before

the

count

is

0,

then

all

the

user

programs below

it

are

terminated.

An

executive

program

can

clear

the

fork

structure

of

a

job

by

putting

the

job

number

in

A and

executing

BRS

22.

The

effect

is

as

though enough

rubouts

had

occurred

to

send

the

job

back

to

the

top-level

executive

fork.

The

panic

Which

returns

a

status

word

of

1

is

caused

by

the

execution

of

an

illegal

instruction

in

the

fork.

Illegal

instructions

are

of

two

kinds:

1)

Machine

instructions

which

are

privileged

2)

SYSPOPs

which

are

forbidden

to

the

user

or

which have

been

provided

with

unacceptable

arguments.

If

interrupt

2

is

armed and

the

fork

is

executive,

interrupt

2

will

occur

instead

of

an

illegal

instruction

panic.

A

status

word

of

2

is

returned

by a

memory

panic.

This

may

be

caused

by

an

attempt

to

address

more

memory

than

is

permitted

by

the

machine

size

which

the

user

has

set,

or

by

an

attempt

to

store

into

a

read-only

block.

If

interrupt

2

is

armed,

it

will

occur

instead

of

the

memory

panic.

Every complete

fork

structure

is

associated

with

a

job,

which

is

the

fundamental

entity

thought

of

as

a

user

of

the

system,

from

the

system's

own

point

of

view.

The

job

number

appears

in

the

PAC

table

entry

for

every

fork

in

the

job's

fork

structure.

In

addition

there

are

several

tables

indexed

by

job

number. These

are

shown

on page

3B,

and

indicate

more

or

less

what

it

is

that

is

specifically

associated

with

each

job.

3B

TSDA

drum

address

of

TS

block

TTNO

teletype

associated

with

this

job

ETI'B amount

of

CPU

time

used

DBA

drum

blocks

available

QUR

time

left

in

long

quantum

Job

Tables

4-1

4.0 Program

Interrupts

A

facility

isprovideci

in

the

monitor

to

simulate

the

existence

of

hardware

interrupts.

There

are

20

possible

interrupts;

four

are

reserved

for

special

purposes

and

16

are

available

to

the

programmer

for

general

use.

A

,fork

may

arm

the

interrupts

by

executing

BRS

78

with

a

2O-bit

mask

in

the

A

register.

This

causes

the

appropriate

bits

in

PTh1

to

be

set

or

cleared

according

to

whether

the

corresponding

bit

in

the

mask

is

1

or

O.

Bit

4

of

A

corresponds

to

interrupt.

number

1,

etc.

No

other

action

is

taken

at

this

time.

When

an

interrupt

occurs

(in

a manner

to

be

described)

the

execution

of

an

SBRM*

to

location

200

plus

the

interrupt

number

is

simulated

in

the

fork

which armed

the

interrupt.

Note

that

the

program

counter

which

is

stored

in

the

case

is

the

location

of

the

instruction

being

executed

by

the

fork

which

is

interrupted,

not

the

location

in

the

fork

which

causes

the

interrupt.

The

proper

return

from an

interrupt

is

a

BRU

to

the

location

from which

the

interrupt

occurred.

This

will

do

the

right

thing

in

all

cases

including

interrupts

out

of

input-

output

instructions.

A

fork

rnay

generate

an

interrupt

by

executing

ERS

79

with

the

number

of

the

desired

interrupt

in

the

A

register.

This

number

may

not

be

one,

two,

three

or

four.

The

effect

is

that

the

fork

structure

is

scanned,

starting

with

the

forks

parallel

to

the

one

causing

the

interrupt

and

proceeding

to

those

above

it

in

the

hierarchy

(i.e.,

to

its

ancestors)

. The

first

fork

encountered

during

this

scan

vlith

the

appropriate

interrupt

mask

bit

set

is

interrupted.

Execution

of

the

program

in

the

fork

causing

the

interrupt

continues

without

disturbance.

If

no

interruptable

fork

is

found,

the

interrupt

instruction

is

treated

as

a

NOP;

otherwise,

it

skips

on

return.

Interrupts

1

and

2

are

handled

in

a

special

way.

If

a

fork

arms

interrupt

1,

a program

panic

(ERS

10

or

rubout

button)

which

would

normally

terminate

the

fork

which

has

armed

interrupt

1,

will

instead

cause

interrupt

1

to

occur,

that

is,

will

cause

4-2

the

execution

of

an

SBRM*

to

location

201.

This

permits

the

programmer

to

control

the

action

taken

when

the

rub

out

button

is

pushed

without

establishing

a

fork

specifically

for

this

purpose.

If

pushinG

the

rubout

button

causes

an

interrupt

to

occur

rather

than

terminating

a

fork,

the

input

buffer

will

not

be

cleared.

If

a memory

panic

occurs

in

a

fork

which

has

anned

interrupt

2,

it

will

cause

interrupt

2

to

occur

rather

tha.n

terminatin;;

the

fork.

If

an

illeF.'-al

instruction

panic

occurs

in

an

executive

fork

which

has

armed

interrupt

2,

it

will

cause

interrupt

2

to

occur

rather

than

terminating

the

fork.

Interrupt

3

is

caused,

if

armed, \·,hen

any

subsidiary

fork

terr:1inates.

Interrupt

4

is

caused,

if

armed, \{hen

any

input-

output

condition

occurs

1<[hich

sets

a

flag

bit

(end

of

record,

end

of

file

and

error

conditions

can

do

this).

vfuenever any

interrupt

occurs,

the

corresponding

bit

in

the

interrupt

mask

is

cleared

and

must

be

reset

explicitly

if

it

is

desired

to

keep

the

interrupt

on.

Note

that

there

is

no

restriction

on

the

number

of

forks

which

may

have

an

interrupt

on.

To

read

the

interrupt

mask

into

A,

the

proGram

may

execute

BRG

49.

5.0

The Swapner

arid

Memory

Allocation

Pseudo-re~abeling

The

940

hardware

allows

the

user's

address

space

to

be

fragmented

into

eight

pages

of

2048

words

each.

This

means

that

the

monitor

must

keep

track

of

eight

drum

addresses

for

each

process.

This

is

done by means

of

eight

six-bit

pseudo-

relabeling

registers.

Each

of

these

registers

is

an

index

to

a

table

which

contains

the

drum

address

of

the

user's

page.

This

table

is

called

the

Private

Memory

Table

(PMT)

and

is

held

in

the

job's

TS

block.

Each

of

the

64

entries

in

RvlT

has

the

following

format:

¢ s I E I R

IE

I

H I X ! 0 P I

I j 1 . drum

address

¢

o 1 2

3·4

17

23

EX

-

Process

must be

executi.ve

to

reference

the

page.

RO

-Read

only

(attempt

to

store

will

generate

a

trap).

SH

-

Shared.

EP -

Will

be

d.estroyed

when

not

in

any

map.

During

the

startup

for

each

user,

the

system

copies

the

first

NCMEM

(currently

35)

entries

out

of

a

resident

table

called

the

Shared

Memory

Table

(SMT)

into

the

new

PMT.

These

entries

describe

memory

that

most

processes

will

need,

such

as

the

monitor,

the

exec,

and

some

of

the

subsystems.

ThUS,

a

program

has

a

max:im.um

of

(64 -

NCMEM)

private

pages.

When

a program

is

run,

his

TS

block

is

swapped and

its

pseudo-relabeling

registers

(in

the

PACT

table)

are

used

to

read

out

the

proper

bytes

from

PMT

and

construct

a

list

of

5-1

drum

pages

that

may

need

to

be

read

from drum.

When

this

list

has

been

constructed,

the

current

state

of

core

is

examined

to

determine

whether

any

blocks

need

to

be

written

out

to

make

room

for

these

which must

be

read

in.

If

so,

a

list

of

blocks

to

be

written

out

is

constructed.

The drum

command

list

is

then

5-2

set

up

with

the

appropriate

commands

to

write

out

and

read

in

the

necessary

blocl\:s.

In

the

course

of

optimizing

the

drum

commands,

the

swapper

may

skip

a

sector.

If

this

is

the

case,

it

searches

through

the

~mory

tables

and

writes

out

a

dirty

page

in

that

sector.

The

scheduler

then

simply

hangs up

until

the

swapping

is

complete.

In

the

scan

which

sets

up

the

drum

read

commands,

the

swapper

collects

from

DHT

the

actual

absolute

memory

addresses

of

the

page

called

for

by

the

pseudo-

relabeling

and

constructs

a

set

of

real

relabeling

registers

which

it

puts

in

two

fixed

locations

in

the

monitor.

It

then

outputs

these

relabeling

registers

to

the

hardware

and

activates

the

program.

There

are

two BRS's which

permit

the

user

to

read

and

write

his

pseudo-relabeling.

BRS

43

reads

the

current

pseudo-

relabelin(~

registers

into

A and

B.

BRS

44

takes

the

contents

of

A and B and

puts

then:

into

the

current

pseudo-relabeling

registers.

An

executive

program

may

set

the

relabeling

registers

in

arbitra.ry

fashion

b~{

using

this

instruction.

A

user

program,

however,

may

add

or

delete

only

blocks

which do

not

have

the

executive

bit

set

tn

FMT.

This

prevents

the

user

from

gaining

access

to

executive

blocks

whose

destruction

may

cause

damage

to

the

system.

Note

that

the

user

is

doubly

restricted

in

his

access

to

real

memory,

firstly,

because

he can

only

access

real

memory which

is

pointed

to

by

his

pseudo-relabeling,

and

secondly,

because

he

is

only

nllo

.....

,ed

to

adjust

those

portions

of

his

pseudo-

relabeling

which

are

not

executive

type.

The

user

can

also

set

the

relabeling

of

a

fork

when

he

creates

it.

See

Section

3.

The same

restrictions

on

manipulation

of

executive

blocks

of

course

apply.

The

system

maintains

a

pair

of

relabeling

registers

which

the

executive

and

various

subsystems

think

of

as

the

user's

program

relabeling.

For

the

convenience

of

subsystems,

any

program

can

read

these

registers

with

BRS

116 and

set

them

with

BRS

117.

5-3

The

memory

allocation

a.lgorithm

is

described

on

page

3-2.

A

user

can

release

a

block

which

is

in

his

current

relabeling

by

putting

any

address

in

that

block

into

A and

executing

BRS

!t.

The

PMT

entry

for

the

block

is

removed and

in

any

other

fork

which

has

this

PMT

byte

in

its

relabeling,

the

byte

is

cleared

to

o.

Equivalent

to

BRS

4

is

BRS

121,

which

takes

a

pseudo-

relabeling

byte

in

A

rather

than

an

address.

An

inverse

operation

is

BRS

120,

which

takes

a

pseudo-relabeling

byte

in

A,

generates

an

illegal

instruction

trap

if

the

corresponding

PMT

entry

is

occupied,

and

otherwise

obtains

a

new

page

and

puts

it

in

that

entry.

This

is

an

exec-only

operation

and

is

implemented

parti-

cularly

for

the

Exec

'RECOVER

FROM

FILE'

operation.

If

A

is

0,

BRS

120

assigns

a

2K

page

and

skips;

this

operation

is

not

exec-

only.

Shared

Memory.

The

system

maintains

a

table

called

the

shared

memory

table

(SMT)

which

describes

all

the

memory

which

can

be

shared

between

jobs

in

the

system.

All

the

cornmon

subsystems

occupy

positions

in

SMT,

and

some

part

of

SMT

is

copied

into

each

job's

FMT

permanently.

To

run

a

subsystem,

the

exec

must

determine

if

the

subsystem

map

is

already

in

PMT

(which

it

will

be

if

all

the

bytes

are

below

NCMEM)

and,

if

not,

arrange

for

the

bytes

to

be

put

into

PMT.

The

exec

makes an

entry

in

SMT

by

executing

BRS

68

with

a

byte

ntunber

in

A.

The

block

addressed

by

the

specified

byte

in

the

pseudo-relabeling

registers

is

put

into

SMT

and

the

pointer

in

SMT

of

this

byte

is

returned.

By

putting

an

index

in

SMT

in

A and

executing

BRS

69,

the

SMT

entry

is

copied

into

the

first

free

byte

of

a

userts

PMT

and

the

byte

number

is

returned

in

A.

The

read-only

bit

in

the

SMT

entry

is

propagated

to

the

PMT

entry

thus

created.

To

delete

an

entry

in

SMT,

the

exec

may

deliver

its

index

in

A

and

execute

BRS

70.

The

user

may

declare

a

block

read-only

by

executing

BRS

80

with

the

pseudo-relabeling

byte

number

of

the

block

in

A and

with

bit

0

of

A

set.

To

make

a

block

read-write,

bit

°

of

A

5-4

should

be

clear.

Bit

0

of

A

will

be

reset

if

the

block

was

formerly

read-write

or

set

if

it

was

formerly

read-only.

If

the

program

doing

this

is

not

an

executive

program,

then

the

block

must

not

be

an

executive

block.

Only

executive

programs

may

make

a

shared

page

read-write.

The drum

is

divided

into

84

bands,

each

containing

16,000

words

arranged

in

8

blocks

of

2K

each.

Up

to

'72

of

these

bands

may

be

used

by

the

swapper

for

program

storage.

A

bit

table

is

maintained

to

indicate

the

availability

of

2K

blocks

in

these

bands.

The

table

consists

of

8 words,

each

containing

24

bits,

one

for

each

band.

If

a

bit

is

zero,

it

indicates

that

the

block

is

in

use.

If

it

is

set,

the

block

is

available.

wllen

the

user's

memory

is

acquired,

it

is

written

as

nearly

as

possible

in

adjacent

blocks,

so

that

it

rnay

be

read

in

without

undue drum

latency

time.

Rotational

positions

are

chosen

by

adding,

mod

8,

the

user's

job

number

to

the

PMT

byte

number

of

the

new

block.

It

should

be

noted

that

whenever a

user

is

activated,

all

of

the

memory

in

his

current

relabeling

registers

is

brought

in.

The

user

does,

however, have

considerable

control

over

precisely

what memory

will

be

brought

in,

because

he

can

read

and

set

his

own

relabeling

registers.

He

may

therefore

establish

a

fork

with

a

minimal

amount

of

memory

in

order

to

speed

up

the

swapping

process

if

this

is

convenient.

To

make

a

block

executive,

execute

BRS

56

with

the

same

argument

as

for

BRS

80,

make

block

read-only.

This

instruction

is

legal

only

for

executive

type

programs.

Real

memory

is

housekept

by

means

of

several

tables.

The

most

important

of

these

is

a

table

(hash)-indexed

by

drum

address

which

describes

all

those

drum

pages

which

are

currently

in

core.

The

Drum

Hash

Table

(DHT)

has

more

entries

than

core

pages.

An

entry

has

the

following

format:

IF

Drum

Core

Address

Address

¢

18

27

F

==

Free

entry

5-5

The

core

address

field

of

DHT

indexes

two

tables

called

the

real

memory

table

(RMT)

and

the

real

memory

use

count

table

(RMe).

An

RMC

entry

is

-1

if

a

page

is

not

in

use;

otherwise,

it

is

one

less

than

the

number

of

reasons

why

it

is

in

use.

Every

occurrence

of

the

page

in

the

relabeling

of

a

process

which

is

running

or

about

to

be

run

counts

as

such

a

reason.

In

addition,

other

parts

of

the

system

can

increment

an

RMC

word

to

lock

a

block

in

core.

No

block

with

non-negative

RMC

will

be

used

by

the

swapper.

The

format

of

an

RMT

entry

(one

per

real

page)

is

4 5 6

2 D E 9

0-0

23

0 I R 0

R R W R

address

of

DHT

entry

¢ ¢ T I I

~

responsible

y p P T

RIP -drum

read

in

progress

DIRTY

-Page

has

been

modified

WIP

-drum

write

in

progress

ERRBIT

-drum

read

error

There

is

one more

table

indexed

by

real

memory,

called

the

real

memory

aging

table.

Whenever

the

swapper

is

entered,

every

word

in

this

table

is

shifted

right

one

bit.

All

blocks

which

show up

in

the

real

relabeling

computed from

the

pseudo-relabeling

with

which

the

swapper

was

entered

then

have

bit

I

turned

on.

The

blocks

with

lowest

RMA

are

selected

for

swapping

out;

of

course,

their

RMC

entries

must

be

negative.

BRS

140

scans

through

the

real

memory

tables

and

for

each

page

with

a

negative

RMC

takes

one

of

two

actions:

If

the

page

is

not

dirty,

the

PMT/SMT

entry

is

marked

as

on drum and

RMT

is

emptied.

If

the

page

is

dirty,

a

write

is

started.

This

has

the

affect

of

forcing

core

and drum

copies

of

most

pages

to

correspond.

6-1

6.0

Miscellaneous

Features

A

user

may

dismiss

his

program

for

a

specified

length

of

real

time

by

executing

BRS

81

with

the

number

of

milliseconds

for

which he

wishes

to

be

dismissed

in

A.

At

the

first

available

opportunity

after

this

time

has

been

exhausted,

his

program

will

be

reactivated.

This

feature

is

implemented

with

a

special

activation

condition

and

the

value

of

the

clock

at

the

time

when a

user

is

to

be

reactivated

is

kept

in

PA.

The

activation

condition

causes

the

current

value

of

the

clock

to

be

compared

with

this

value.

When

the

clock

becomes

greater,

it

is

time

to

reactivate

the

program.

He

can

read

the

real-time

clock

into

A

by

executing

BRS

42.

The number

obtained

increments

by

one

every

1/6Oth

of

a

second.

Its

absolute

magnitude

is

not

significant.

He

can

read

the

elapsed

time

counter

in

A

by

executing

BRS

88.

This

number

is

set

to

0 when he

enters

the

system

and

increments

by

I

at

every

1/60th

second

clock

interrupt

at

which

his

program

is

running.

To

obtain

the

da,ta and

time,

he

can

execute

BRS

39.

This

puts

six

8-bit

characters

into

AB.

These

characters

contain,

in

order,

the

year,

month, day,

hour

(0-23),

minute

and

second

at

which

the

instruction

is

executed.

A

user

may

dismiss

his

program

until

an

interrupt

occurs

or

the

fork

in

question

is

terminated

by

executing

BRS

109.

A

program

can

test

whether

it

is

executive

or

not

by

executing

BRS

71,

which

skips

in

the

former

case.

An

executive

program

can

dismiss

itself

explicitly.

See

Section

2.

There

are

some

operations

designed

for

so-called

executive

BRSs, which

operate

in

user

mode

with

a

map

different

from

the

one

they

are

called

from.

BRS

111

returns

from one

of

these

BRSs,

transmitting

A,

B and X

to

the

calling

program

as

it

finds

them.

BRS

122

simulates

the

addreSSing

of

memory

at

the

location

specified

in

A.

If

new

memory

is

assigned,

it

is

put

into

the

relabeling

of

the

calling

program. A

memory

panic

can

occur,

in

which

case

it

appears

to

the

calling

program

that

it

comes

from

the

BRS

instruction.

BRS

141

reads

the

panic

table

of

the

caller,

and

BRS

142

sets

the

state

from a

table

specified

by

X.

6-2

An

executive

program can

cause

an

instruction

to

be

executed

in

system

mode

by

addressing

it

with

EXS.

7-1

7.0

Teletype

Input-Output

We

begin

with

an

outline

of

the

implementation

of

the

teletype

operations.

This

may

serve

to

clarify

the

exact

disposal

of

the

characters

which

are

being

read

and

written.

Every

teletype

has

attached

to

it

a

table

which

is

shown

in

Figures

7A

and 7B.

No

buffers

are

attached

to

the

teletype

unless

input

from

or

output

to

the

teletype

is

taking

place.

As

characters

are

output

by

the

program,

buffers

are

attached

to

the

teletype.

These

buffers

are

released

as

soon

as

they

are

emptied

by

the

teletype

interface.

On

input

buffers

are

attached

to

the

teletype

as

characters

are

received

from

the

teletype,

and

they

are

released

as

soon

as

the

program

empties

them.

Input

and

output

buffers

are

logically

and

physically

independent,

although

they

come

out

of

the

same

buffer

pool.

When

a

character

is

typed

in

on a

teletype)

it

is

converted

to

internal

form and added

to

the

input

buffer

unless

it

is

rubout

on a

controlling

teletype.

The

treatment

of

rubouts

is

discussed

in

Section

3. The

echo

routine

address

is

then

obtained

from

TTYTBL

and

called.

It

figures

out

what

to

echo

and

whether

or

not

the

character

is

a

break

character.

The

available

choices

of

echos

and

break

characters

are

listed

below.

If

the

character

is

a

break

character,

and

if

a

user's

program

has

been

dismissed

for

teletype

input,

it

will

be

reactivated

regardless

of

the

number

of

words

in

the

input

buffer.

In

the

absence

of

a

break

character,

the

user's

program

is

reactivated

only

when

the

input

buffer

is

nearly

full.

If

the

teletype

is

in

the

process

of

outputting

(TOS2

>

-1)

then

the

character

to

be

echoed

is

put

into

the

last

byte

of

the

buffer

word which

contains

the

input

character.

When

the

character

is

read

from

the

buffer

by

the

program,

the

echo,

if

any,

will

be

generated.

This

mechanism,

called

deferred

echoing,

permits

the·

user

to

type

in

while

the

teletype

is

outputting

without

having

his

input

mixed

with

the

teletype

output.

7-2

There

are

four

standard

echo

routines

in

the

system,

referred

to

by

the

numbers

0,

1,

2 and 3. a

is

a

routine

in

which

the

echo

for

each

character

is

the

character

itself,

and

all

cha.racters

are

break

characters.

Routine

1

has

the

same

echoes,

but

all

characters

except

letters,

digits,

and

space

are

break

characters.

Routine

2

again

has

the

same

echoes,

but

the

only

break

characters

are

control

characters

(including

carriage

return

and

line

feed).

Routine

3

specifies

no

echo

for

any

character,

and

all

characters

are

break

characters.

This

routine

is

useful

for

a

program

which

wishes

to

compute

the

echo

itself.

To

set

the

echo

routine,

put

the

teletype

number

in

X and

the

echo

routine

number

in

A and

execute

BRS

12.

Note

that

BRS

12

is

also

used

to

turn

on

8-level

mode

(see

below).

To

read

the

echo

routine

number

into

A,

put

the

teletype

number

in

X and

execute

BRS

40.

This

operation

returns

in

A

the

word

listed

as

TTYTBL

on

page

7A.

To

input

a

character

from

the

controlling

teletype

(the

teletype

on which

the

user

of

the

program

is

entered)

into

location

M

in

memory

the

SYSPOP

Tel

M

(teletype

character

input)

is

used.

This

SYSPOP

reads

the

character

from

the

teletype

input

buffer

and

places

it

into

the

8

rightmost

bits

of

location

M.

The

remainder

of

location

M

is

cleared.

The

character

is

also

placed

in

the

A

register,

whose

former

contents

are

destroyed.

The

contents

of

the

other

internal

registers

are

preserved

by

this

and

all

the

other

teletype

SYSPOPs

and

BRS's.

To

output

a

character

from

location

M,

the

SYSPOP

TCO

M

(teletype

character

output)

is

used.

This

instruction

outputs

a

character

from

the

rightmost

8

bits

of

location

M.

In

addition

to

the

ordinary

ASCII

characters,

7-3

all

teletype

output

operations

will

accept

135

(octal)

as

a

multiple

blank

character.

The

next

character

will

be

taken

as

a

blank

count,

and

that

many

blanks

will

be

typed.

The

TTYTIM

cell

in

the

teletype

table

is

set

to

the

current

value

of

the

clock

whenever

any

teletype

activity

(interrupt

or

output

SYSPOP)

occurs.

The

top

bit

is

left

clear

unless

the

activity

is

a

rubout

input.

This

cell

is

checked

by

the

rubout

processor

to

determine

whether

the

rubout

should

reset

the

job

to

the

exec.

See

p.

3-6.

Every

teletype

in

the

system

is

at

all

times

in

one

of

three

states:

a)

It

may

be

the

controlling

teletype

of

some

user's

program.

It

gets

into

this

state

when

a

user

enters

on

it.

b)

It

may

be

attached

to

some

user

in

a manner

about

to

be

described.

c)

It

may

be

completely

free.

The

status

of

the

teletype

is

reflected

by

the

contents

of

TTYASG.

There

are

mechanisms

to

be

described

by

which

the

user

may

direct

output

to

any

teletype

in

the

system which

is

willing

to

a.ccept

it

and

receive

input

from

any

teletype

which

is

not

free.

If,

however, he wishes

to

have

better

control

over

a

teletype

(for

instance,

to

prevent

other

users

from

accessing

it)

he

may

attach

it

by

executing

the

instructions

LDA

=teletype

number

BRS

27

If

the

indicated

teletype

is

free,

it

is

attached

to

the

user

whose

program

executes

the

instruction,

and

the

BRS

will

skip.

Otherwise

the

teletype

status

is

not

affected,

and

the

BRS

does

not

skip.

In

the

following

discussion

we

will

say

that

a

teletype

is

attached

to

a

user

even

if

it

is

the

controlling

teletype.

To

release

an

already

attached

teletype,

execute

the

instructions

LDA

=teletype

number

BRS

26

If

the

specified

teletype

is

not

already

attached

to

the

user,

this

is

an

illegal

instruction

and

causes

a

panic.

All

attached

teletypes

are,

of

course,

released

when

the

user

logs

out.

7-4

A

teletype

becomes a

controlling

teletype

if

it

is

dormant

and

rubout

is

pushed on

it.

It

can

be

returned

to

its

dormant

state

by

BRS

112,

which

takes

the

job

number

of

the

job

associated

with

the

teletype

in

X.

A

job

may

terminate

itself.

This

operation

also

releases

all

teletypes

attached

to

the

job.

The

user

may

specify

for

his

controlling

teletype

or

for

one

which he

has

attached,

whether

or

not

messages from

outside

will

be

accepted,

and

whether

or

not

input

from

outside

will

be

accepted.

The former

condition

is

governed

by

the

accept

messages

bit,

the

latter

by

the

accept

input

bit.

The

accept

message

bit

controls

execution

of

OST

instructions

and

the

setting

of

teletype

output

links.

The

accept

input

bit

controls

execution

of

STI

instructions

and

the

setting

of

teletype

input

links.

To

set

these

bits,

the

user

may

execute

LDA

=teletype

number

LDA

BrrS

BRS

25

The

last

bit

of

BITS

will

set

the

accept

input

bit,

the

next

to

last

the

accept

messages

bit.

Setting

or

clearing

these

bits

will

not

affect

any

teletype

links

currently

active.

To

do

input

and

output

to

specified

teletypes

(rather

than

implicitly

to

a

controlling

teletype

as

in

TCI

and

TCO)

the

SYSPOPs

1ST

and

OST

are

available.

To

input

a

character

from

a

specified

teletype,

execute

the

instruction

IST

=teletype

number

(input

from

specified

teletype)

which

brings

the

character

into

the

A

register.

This

instruction

is

illegal

unless

the

teletype

is

attached

to

the

user.

To

output

a

character

to

a

specified

teletype,

execute

the

instructions

LDA

=cha.racter

OST

=teletype

number

(output

to

specified

teletype)

This

instruction

is

illegal

if

the

following

three

conditions

are

satisfied:

(1)

The

spec

ified

te

letype

is

not

atta.ched

to

the

user,

(2)

The

specified

teletype

does

not

have

its

accept

messa.ges

bit

set,

(3)

The

program

executing

an

instruction

is

a

user

rather

than

an

executive

program.

If

these

conditions

are

7-5

satisfied,

an

illegal

instruction

panic

will

be

generated.

Note

that

attached

teletypes

do

not

have

the

same

status

as

the

controlling

teletype

for

a

user.

In

particular,

pushing

the

rub

out

button

on an

attached

teletype

will

have no

effect.

The

instruction

eIO

=teletype

number +

1000

is

exactly

equivalent

to

IST

=teletype

number.

The

instruction

eIO

=teletype

number +

2000

is

exactly

equivalent

to

OST

=teletype

number.

This

mechanism

permits

the

user

to

do

Ilo

to

specified

teletypes

within

the

frrumework

of

the

sequential

file

machinery.

The

user

has

considerable

control

over

the

state

of

the

teletype

buffers

for

the

teletypes

attached

to

him.

In

particular,

he

may

execute

the

following

BRS's.

All

these

take

the

teletype

number

in

X.

Recall

that

·-1

may

be

used

for

the

controlling

teletype.

BRS

11

BRS

29

BRS

13

BRS

14

BRS

138

clears

the

teletype

input

buffer.

clears

the

teletype

output

buffer.

skips

if

the

teletype

input

buffer

is

empty.

waits

until

the

teletype

output

bu~fer

is

empty.

waits

until

a

process

gets

dismissed

because

the

input

buffer

is

empty.

There

is

one

additional

piece

of

machinery which

permits

output

to

go

to

a

teletype

other

than

the

controlling

teletype.

This

machinery

is

~plied

by

the

top

bits

of

TTYTBL,

which

specify

whether

any

link

bits

are

set.

Associated

with

each

teletype

are

two words

called

the

absolute

input

link

control

word

(LeW)

and

the

absolute

output

LCW.

Each

of

these

words

contains

one

bit

for

each

teletype

in

the

system.

If

the

bit

for

teletype

m

is

set

in

the

input

LCW

for

teletype

n,

every

chs.racter

which goes

into

n'

s

input

buffer

will

also

go

into

m's

input

buffer.

If

the

bit

is

set

in

the

output

LCW,

every

character

which

is

output

to

n,

including

echoes,

will

also

be

output

to

m.

7-6

Also

associated

with

each

teletype

are

relative

LCW's

for

input

and

output.

The

bits

in

these

LCW's

are

set

by

BRS

23. Each

time

any

relative

WW

is

changed,

the

absolute

LCW'

s

are

all

recomputed.

The

Boolean

matrix

formed

by

the

absolute

input

(output)

LeW's

is

the

infinite

product

of

the

matrix

of

the

relative

input

(output)

LCW's.

The

instructions

LDX

=teletype

number

LDA

=TABLE

LDB

CTL

BRS

23

will

set

one

of

the

relative

LCW'

s

for

the

indicated

teletype.

TABLE

is

the

address

of

a

list

of

teletype

numbers

terminated

with

-2.

The

bits

of

CTL

are

interpreted

as

follows:

o O=output

LCW

l=input

ICW

1

2

O=clear

all

links

first

l=do

not

clear

links

first

O=set

link

bits

for

teletypes

whose numbers

are

in

the

table.

l=clear

link

bits

for

teletypes

whose numbers

are

in

the

table.

Fran

the

old

relative

LCW

and

the

information

supplied

by

BRS

23

a

new

relative

LCW

is

created.

New

absolute

LCW's

for

all

teletypes

are

then

computed.

An

output

link

can

be

set

up between two

teletypes

only

if

each

of

the

teletypes

satisfies

at

least

one

of

the

following

conditions:

a)

It

is

the

controlling

teletype

of

the

program

executing

BRS

23

b)

It

is

attached

to

the

program

c)

Its

accept

messages

bit

is

on

(destination

only)

d)

The

fork

executing

the

ERS

is

executive.

An

input

link

can be

set

only

if

the

same

conditions

are

satisfied

for

the

accept

input

bit.

7-7

To

clear

all

liIL~S}

input

and

output,

to

or

from a

teletype,

execute

LDX

=teletype

number

BRS

24

Special

provision

is

made

for

reading

8-bit

codes

from

the

teletype

without

sensing

rub

out

or

doing

the

conversion

from

ASCII

to

internal

which

is

done

by

TCI.

To

switch

a

teletype

into

this

mode,

execute

LDX

=teletype

number

LDA

=terminal

character

+

40000000B

BRS

12

This

will

cause

each

8-bit

character

read

from

the

teletype

to

be

transmitted

lli~changed

to

the

user's

program.

The

teletype

can

be

returned

to

normal

operation

by

1.

Reading

the

terminal

character

specified

in

A,

or

2.

Setting

the

echo

table

with

BRS

12.

No

echoes

are

generated

while

the

teletype

is

in

8-level

mode.

Teletype

output

is

not

affected.

A

parallel

operation,

BRS

85,

is

provided

for

8-level

output.

BRS

86

returns

matters

to

the

normal

state,

as

does

any

setting

of

the

echo

table.

To

simulate

teletype

input,

the

operation

STr

=teletype

number

is

available.

STI

puts

the

character

in

A

into

the

input

buffer

of

the

specified

teletype.

It

is

legal

if

the

accept

input

bit

is

on.

To

steal

teletype

output,

the

operation

STO

=teletype

number

takes

a

character

from

the

teletype's

output

buffer

and

returns

it

in

A.

STO

is

legal

only

if

the

accept

input

bit

is

on.

To

disable

output

from a

buffer

to

a

teletype,

execute

BRS

139

with

the

teletype

number

in

X.

If

bit

¢

of

A

is

1,

the

NO

bit

will

be

set;

otherwise,

the

NO

bit

will

be

cleared.

TTYOB

TTYOBC

TELETYPE

SYSTEM

POINTERS

Pointer

to

next

available

buffer

in

buffer

pool

Count

of

available

buffers

in

buffer

pool

7A

TTYTBL

N N A S S I 0 A A A

10

address

of

echo

routine

23

S 0 P I 0 L L K I M

TTYBRK

TTYASG

ROLCW

RILCW

Waiting

for

break

character

when

-1

PACPl'R

of

fork

to

terminate

on

rub

out

3 7 7 7 7

1

18

controlling

Relative

output

link

control

word

Relative

input

link

control

word

TTY

Status

active

inactive

. b 23

JO

attached

TTYTIM

R

B

value

of

clock

when

last

action

occurred

on

this

tty

TTYDEV

device

(normally

physical

teletype)

using

this

buffer.

NS

=

not

linked

or

8-level

AM

=

accept

message

IL =

input

linked

OL

=

output

linked

NO

=

don't

output

to

TTY

interface

AK

=

accept

input

links

AI =

accept

input

8I

=

8-level

input

SO

=

8-level

output

RB

=

last

action

was

input

of

rubout

AP

=

accept

output

links

7B

TELETYPE

TABLE

TIS2 number

of

characters

in

input

buffer

TIS4

next

available

space

in

input

buffer

(pointer)

7 8

bits

'7

and

8:

o 1

1 0

1 1

10

I

WORD

ADDRESS

byte

1

byte

2

byte

3

23

TIS5

next

filled

space

in

input

buffer

(pointer

with

same

format

as

TIS4)

TIS6

deferred

echo

byte

count.

Input

characters

are

echoed

when

the

NO

bit

is

set

in

TTYTBL

and

this

count

goes

negative.

It

TIBBl

TIBB2

TIBLC

TOS2

TOS3

TOs4

TOS5

Tos6

TOBBl

TOBB2

TOBIC

TTYPN

TTYLN

is

decremented

when

a

character

is

taken

out

of

the

input

buffer.

word

pointer

to

the

oldest

acquired

input

buffer:

=0 no

buffer

attached

word

pointer

to

the

last

acquired

input

buffer

count

of

input

buffer

that

can

be

acquired

number

of

characters

in

output

buffer:

-1

=

inactive

< 0 =

not

in

mult

iple

blank

mode; 400 =

just

saw 135

(multiple

blank

character);

other

= number

of

blanks

next

filled

space

in

output

buffer

(pointer

same

as

TIS4)

next

available

space

in

output

buffer

(pointer

same

as

TIS4)

< 0 =

not

terminated

during

output

to

links;

> 0 =

next

link

that

output

has

to

be

sent

to.

word

pointer

to

oldest

acquired

output

buffer;

= 0 no

buffer

attached

word

pointer

to

last

acquired

output

buffer

count

of

output

buffers

that

can

be

acquired

contains

physical

teletype

number

associated

with

this

buffer,

or

4B7

if

no

physical

teletype

attached

contains

logical

teletype

buffer

associated

with

this

physical

teletype

or

zero

(¢)

if

no

buffer

is

attached.

7C

TELETYPE

BUFFERS

TTYOC

1

1.

2 3

2.

1-----0004

N

1-----

....

BUFFER

POOL

POINTERS

TOBBl

1

TOBB2IL--_3_~

TOS41

lX1

1.

+N

I

1.

2

1-----

....

2.

3 3·

lXl=

byte

count

in

word

N = word

displacement

in

buffer.

PROGRAM

OUTPUT

BUFFER

PO:rnTERS

8-1

8.0

Drum

and

Buffer

Organization;

Devices

8.1

File

Storage

on

the

Drum

The drum

is

divided

into

two

major

sections,

program

swapping

and

file

storage.

The

organization

of

the

program swapping

area

is

discussed

in

Section

5.

The

file

storage

area

is

divided

into

256 word

blocks

which form

the

physical

records

for

storage

of

files.

Every

file

has

one

or

more

index

blocks

which

contain

pointers

to

the

data

blocks

for

the

file.

An

index

block

is

a

256 word

block,

as

are

all

other

physical

blocks

in

the

file

area.

Only

the

first

141 words

of

the

index

block

are

used,

however,

for

data

storage.

A

couple

of

additional

words

are

used

to

chain

the

index

blocks

for

any

particular

file,

both

forward

and backward. The

index

blocks

for

a

file

contain

the

addresses

for

all

the

physical

blocks

used

to

hold

information

for

the

file.

Available

storage

in

the

file

area

of

the

drum

is

kept

track

of

with

a

bit

table

similar

to

the

table

used

to

keep

track

of

program swapping

storage.

Since

there

are

sixty-four

256-word

blocks

around

the

circumference

of

the

drum and a

maximum

of

72 drum bands

(out

of

the

84

available)

may

be

used

for

file

storage,

a 192-word

bit

table

which

contains

3 words

of

72

bits

for

each

row

of

physical

blocks

suffices.

If

a

bit

in

this

table

is

set,

it

indicates

that

the

corresponding

block

on

the

drum

is

in

use.

Again,

as

with

program

swapping

storage,

the

organization

of

this

table

makes

it

easy

to

optimize

the

writing

of

files.

This

is

done

by

putting

consecutive

physical

blocks

in

the

file

in

alternating

rows on

the

drum.

The

intervening

row

between

each

two

physical

blocks

provides

the

time

for

the

channel

to

fetch

a

new

command

and

the

heads

to

switch.

The

result

of

this

organization

is

that

information

may

be

transferred

from a

file

on

the

drum

into

core

at

one-

half

core

memory

speed

if

conditions

are

right.

8-2

8.2

File

Buffers

Every open

file

in

the

system

with

the

exception

of

purely

character-oriented

files

such

as

the

teletype

has

a

file

buffer

associated

with

it.

The

form

of

this

buffer

is

shown on page

BA.

Part

(a)

of

this

figure

shows

the

buffer

proper,

and

part

(b)

shows

the

index

block

buffer

and

pointers

associated

with

it.

Part

(b)

is

not

used

only

by drum

files,

but

is

present

in

all

cases.

Each

job

has

associated

with

it

a

temporary

storage

block,

which

is

always

the

first

entry

in

the

job's

FMT.

This

block

is

used

to

hold

information

about

the

user

and

for

the

system's

temporary

storage.

It

also

has

room

for

three

buffers.

An

additional

block

may

be

assigned

with

room

for

five

more

buffers

if

more

than

three

file

s

are

open

at

one

time.

The

pseudo-

relabeling

for

the

extra

buffer

block

and

the

TS

block

is

held

in

a

table

called

RL3

which

is

indexed

by

job

number, and

is

put

into

the

monitor

map

whenever

any

fork

belonging

to

that

job

is

run.

Note

that

the

amount

of

buffer

space

actually

used

is

a

fuu~ction

of

the

device

attached

to

the

file.

In

all

cases

the

two

pointer

words

at

the

head

of

the

buffer

indicate

the

location

of

the

data.

The

first

word

points

to

the

beginning

of

the

relevant

data

and

is

incremented

as

data

are

read

from an

input

buffer.

The

second word

points

to

the

end

of

the

data

on

input

or

end

of

the

buffer

on

output

or

written

in

an

output

buffer.

When

the

buffer

is

in

its

dormant

state,

both

words

point

to

the

first

data

word

of

the

buffer.

Whenever any

physical

I/O

operation

is

completed,

the

first

pointer

contains

the

address

of

this

word.

B-3

8.3 Devices

Every

different

kind

of

input-output

device

attached

to

the

system

has

a

device

number.

The

numbers

applicable

to

specific

devices

are

given

in

Section

9;

here

the

various

tables

indexed

by

device

number

are

described.

The

entries

in

these

tables

addressed

by

a

specific

device

number

together

with

the

unit

number

(if

any) and

the

buffer

address,

completely

define

the

file.

All

this

information

is

kept

in

the

file

control

block

(Section

4.3) which

is

addressed

by

the

file

number.

Page

8B

shows

the

tables

indexed

by

device

number. Note

the

multiplicity

of

bits

which

specify

the

characteristics

of

the

device.

Some

of

these

call

for

comment. A

device

may

be

common

(shared

by

users,

who

must

not

access

it

simultaneously;

e.g.,

tape

or

cards)

or

not

common

(e.g.,

drum);

this

characteristic

is

defined

by

NC.

It

may

have

units;

e.g.,

there

may

be

multiple

magtapes.

The

U

bit

specifies

this.

The

DIU

word

indicates

which

file

is

currentLy

monopolizing

the

device;

in

the

case

of

a

device

with

multiple

units,

DIU

points

to

a

table

called

ADIU

which

contains

one word

for

each

unit.

The

major

parameters

of

a

device

are:

-

the

opening

routine,

which

is

responsible

for

the

operation

necessary

to

attach

it

to

a

file.

-

the

GPW

routine,

which

performs

character

and word

I/O.

-

the

BIO

routine,

which

performs

block

I/O.

Minor

parameters

are:

-

physical

record

size

(determining

the

proper

setting

of

buffer

pointers

and

interlace

control

words

for

the

channel).

-

the

expected

t~e

for

an

operation;

the

swapper

uses

this

number

to

decide

whether

it

is

worthwhile

to

swap

the

user

out

while

it

is

taking

place.

8A

pointer

to

first

data

word

in

buffer

pointer

to

last

data

word

1st

data

word

·

·

·

data

block

·

256th

data

word

a)

layout

of

a

file

buffer

drum

address

of

data

block,

or

¢

·

·

·

·

drum

address

of

data

block,

or

'/J

'Z..O)

BFP

pointer

to

next

index

block

1-

()

G BBP

pointer

to

previous

index

block

1

,,7

BDS

log

2

(data

block

size!256)

L'v

BLX

file

length

?- I I

BCK

check

sum

b)

format

of

an

index

block

DEV word

or

character

I/O

routine

BUFS

buffer

size

BDEV

block

r/o

routine

DID

device

in

use

OPNDEV

opening

routine

¢ 1

~

1 ¢

0

I¢

t/J

t/J

1

(/) (/)

GPW

routine

CH

char

oriented

DRM

dru.rn

RX

random

access

BF

requires

buffer

WB

W

buffer

OUT

output

2 ' 3 8 9

l¢

~

I

max.

unit

number U I

physical

record

size

U

check

unit

number

NC

not

common

(i.e.

don't

set

DID)

9

BIO

routine

file

number

using

this

device

or

-1

points

to

ADN

(has

unit

number added)

2 3 8 9

l~

\

~

expected

wait

time

0

opening

subroutine

in

clock

C:lC

Ie

s

EO

exec

only

allowed

to

open

•

DEVICE

INDEXED

TABLES

23

23

23

U = 0

u = 1

23

9-1

9.0

Sequential

Files

9.1

Sequential

Drum

Files

1.94

includes

a

major

revision

to

the

drum

file

system.

Basically,

a

file

appears

as

an

address

space

with

an

arbitrary

upper

bound

called

its

"length."

The

maximum

possible

length

is

around

four

million

words

(22

bits).

The

file

is

internally

paged

into

an

arbitrary

number

of

data

blocks

whose

size

may

be

any power

of

two

larger

than

256

words.

The

following

discussion

will

be

of

interest

to

those

who

need

to

make

efficient

use

of

large,

randomly

accessed

files:

1.

The

data

blocks

are

kept

track

of

by

the

use

of

index

blocks

chained

together.

Each

index

block

can

describe

about

14¢

data

blocks.

Random

access

will

be

slow

if

there

are

several

index

blocks

to

chain

through.

A

large

data

block

size

will

minimize

this

source

of

inefficiency.

2.

Block

transfers

are

implemented

in

the

most

efficient

manner,

with

as

much

as

possible

of

the

data

requested

transferred

directly

into

the

user's

memory.

The

slop

on

either

end

is

buffered

in

256-word

blocks.

Programs

cognizant

of

the

structure

of

their

files

can

avoid

all

buffering.

All

word

operations

use

the

256-word

buffer.

The

user's

access

to

an

open

file

is

housekept

by

means

of

a

position

pointer

to

the

file.

This

pointer

may

be moved

explicit~

by

the

user

or

implicitly

by any

of

the

I/O

operations.

The

I/O

operations

always

leave

the

pointer

pointing

at

the

word

following

the

last

transfer.

eIO

is

a

confusion

factor.

When

a

file

is

opened,

any

of

three

types

of

access

to

that

file

may

be

given

to

the

user:

read,

write,

or

position.

Position

ac~ess

is

intended

to

implement

append-only

files.

You

may

not

move

the

pointer

or

perform

random

operations

unless

you have

position

access

to

the

file.

file

o12ened

as

access

given

sequential

input

r p

sequential

output

w

random

re

ad-only

r p

random

read-write

r w p

The

mechanisms

for

setting

the

length,

data

block

size,

or

for

moving-----ene-po~nter_are

described

undeI

BRS

143-144.

9-2

BRS

66

deletes

the

contents

of

an

open

drum

file.

In

the

case

of

a

sequential

output

file,

it

sets

its

length

to

zero.

You

must have

write

access

to

the

file

to

use

BRS

66.

BRS

67

takes

a

file

number

in

A and

deletes

all

trace

of

the

file.

Use

of

this

BRS

is

limited

to

the

EXEC.

ERS

143, 144 have

been

implemented

as

general

read

and

set

status

of

a

thingy.

The

calling

sequence

is:

A:

table

address

or

data

(depends on

B¢)

If

a

table

address,

A

is

incremented

to

point

to

one

past

the

last

word

transferred.

X:

thingy

number

B:

decodes

as

follows

bit

¢:

~

if

A has

data,

1

if

A

points

to

a

table

bits

1-11:

"type"

of

thingy

bits

12-23:

"attribute"

"type"

is

I

for

a drum

file,

2

for

a

job.

No

other

thingies

have

been

implemented

as

yet.

For

drum

files,

the

attribute

field

specifies

the

following:

1.

(Position)

One

may

read

or

set

the

sequential

I/O

pointer.

The

bottom 22

bits

are

the

current

word

pointer,

the

top

two

the

character

offset.

('/IIJ

means a word

boundary.)

The

offset

must be ¢

if

the

pointer

is

set.

2.

(Length) Reads

or

sets

the

length

of

a

file.

3.

(Sequential

I/O

mode)

The

sequential

I/O

operations

(CIO,

WIO,BIO)

are

interpreted

as

input

if

the

sequential

mode

is

¢,

output

if

the

mode

is

4B7.

9-3

4.

(Capabilities)

Opening a

file

may

give

read/write/position

access

to

the

file.

These

bits

may

be

read

in

bits

21-23.

If

you

try

to

set

them,

they

are

~d

with

the

existing

capabilities.

5.

(Data Block

Size)

Returns

n where 2n+8

is

the

number

of

words

in

a

data

block.

May

be

set

only

if

the

file

length

is

(1.

6. (User words) Each

file

in

the

system

has

five

arbitrary

words

associated

with

it.

Anyone

may

read

them

but

only

the.

exec

may

set

them.

7 . (

"structure")

A

file

may

have

voids

in

it.

If

you

are

interested,

you can

find

out

where

these

are.

BRS

143

returns

the

number

of

words from

the

current

sequential

pointer

to

the

next

transition.

It

also

moves

the

pointer.

If

you

are

crossing

a

void

part

of

the

file

with

this

operation,

the

sign

bit

of

the

number

is

turned

on.

Setting

this

state

with

BRS

144

is

interpreted

by

releasing

this

many

words beyond

the

pointer.

This

also

moves

the

pointer.

8.

(count

data)

Can

only

be

read.

Sets

the

pointer

to

the

beginning

of

the

file.

9. (copy

the

index

block)

Can

only

be

read.

Gives a copy

of

the

entire

index

block.

For

jobs

(type

= 2)

BRS

143 and

144

interpret

the

attribute

field

thusly:

1.

(files)

Returns

a

bit

word

telling

which

files

are

open.

This

word

may

not

be

set.

2.

(mT)

Reads

the

private

part

of

Ht1T.

The

Exec opens a

sequential

drum

file

by

the

following

sequence

of

instructions:

LDX

=device number, 8

(input)

or

9

(output)

LDA

=unit

number,

address

of

first

index

block

BRS

I

If

the

file

is

opened

successfully,

the

BRS

skips;

otherwise,

9-4

it

returns

without

skipping.

Use

of

this

BRS

is

restricted

to

executive

type

programs. User programs

may

access

drum

files

only

through

the

executive

file

handling

machinery.

BRS

I

can

also

be

used

to

open

other

kinds

of

files.

The

device

and

unit

numbers

are

used

to

determine

the

physical

location

of

the

file.

See

Section

9.2.

If

BRS

I

fails

to

skip,

it

returns

in

the

A

register

an

indication

of

the

reason:

-2

too

many

files

open

--

no

file

control

blocks

or

no

buffers

available.

-1

device

already'

in

use.

For

the

drum,

produced

by

an

attempt

to

open a

file

for

input

if

already

open

for

output

or

for

output

if

already

open

at

all.

o

no

drum

space

left.

This

inhibi

ts

opening

of

output

files

only.

See

Section

9.2

for

other

error

conditions.

BRS

I

returns

in

the

A

register

a

file

number

for

the

file.

This

file

number

is

the

handle

which

the

user

has

on

the

file.

He

may

use

it

to

close

the

file

when

he

is

done

with

it

by

putting

it

in

the

A

register

and

executing

BRS

2.

This

severs

his

connection

with

the

file.

BRS

2

is

available

only

to

executive

progrwms,

user

programs

should

use

BRS

20

instead.

To

close

all

his

open

files

an

executive

program

may

execute

BRS

8.

The

corresponding

operation

for

nor.mal

user

programs

is

BRS

17.

Three

kinds

of

input-output

may

be done

with

sequential

files.

Each

of

these

is

specified

by

one

SYSPOP.

Each

of

these

SYSPOPs

handles

input

and

output

indifferently,

since

the

file

9-5

must be

specified

as

an

input

or

an

output

file

when

it

is

opened.

It

is

not

possible

to

have a

file

open

for

both

input

and

output

at

the

same

time:

this

may

be

circumvented

by

using

random

:tiles.

To

input

a

single

character

to

the

A

register

or

output

it

from

the

A

register,

the

instruction

CIO

=file

number

is

executed.

On

input

an

end-of-record

or

end-of-file

condition

will

set

bits

.Q.

and Q

~

I

in

the

file

number

(these

are

called

~

bits)

and

return

a

134

or

137

character,

respectively.

If

interrupt

4

is

armed,

it

will

occur.

The

end-of-record

condition

occurs

on

the

next

input

operation

after

the

last

character

of

the

record

has

been

input.

Note

that

an

end-of-record

condition

only

occurs

for

type

files

and

is

of

concern

only

to

the

Exec.

~

The

end-of-file

condition

occurs

on

the

next

input

operation

after

the

end

of

record,

which

signals

the

last

record

of

the

file.

The

user

may

generate

an

end

of

record

while

writing

a

file

by

using

the

control

operation

to

be

described.

To

input

a word

to

the

A

register

or

output

it

from

the

A

register,

WIO

=file

number

is

executed.

An

end-of-record

condition

returns

a word

of

three

134

characters

as

well

as

setting

the

flag

bit,

and an end

of

file

returns

a word

of

three

137

characters.

If

the

condition

occurs

when

a

partially

filled-out

word

is

present,

the

word

is

filled

out

with

one

of

these

characters.

Mixing word and

character

operations

will

lead

to

peculiarities

and

is

not

recommended.

To

input

a

block

of

words

to

memory

or

output

them from

memory,

the

instructions

LOX

=first

word

address

LDA

=number

of

words

BIO

=file

number

should

be

executed.

The

contents

of

A and X

will

be

destroyed.

The A

register

at

the

end

of

the

operation

contains

the

first

memory

location

not

read

into

or

out

of.

9-6

If

the

operation

causes

any

of

the

flag

bits

to

be

set,

it

is

terminated

at

that

point

and

the

instruction

fails

to

skip.

If

the

operation

is

completed

successfully,

it

does

skip.

Note

that

a

BIO

cannot

set

both

the

EOR

and

the

EOF

bits.

BIO

is

implemented

with

considerable

efficiency

and

is

capable

of

reading

a

file

at

one-half

the

maximum

drum

transfer

rate.

The

flag

bits

(0 and 7)

of

the

file

number

are

set

by

the

system

whenever end

of

file

is

encountered

and

cleared

on any

input-output

operation

in

which

this

condition

does

not

occur.

Bit

0

is

set

on any

unusual

condition.

In

the

case

of

a

BIO

the

A

register

at

the

end

of

the

operation

indicates

the

first

memory

location

not

read

into

or

out

of.

Bit

6

of

the

file

number

may

be

set

on an

error

condition.

Whenever any

flag

bit

is

set

as

a

result

of

an

input-output

operation

in

a

fork,

interrupt

4

will

occur

in

that

fork

if

it

is

armed.

The

user

may

delete

all

the

information

in

a drum

file

by

executing

the

instructions

LDA

=file

number

BRS

66

He

may

also

eliminate

the

file

entirely

by

giving

an

executive

command

described

in

Document R-22,

or

via

ERS

63

(vide

infra).

The

index

block

for

a

sequential

drum

file

contains

one

word

for

each

physical

record

in

the

file.

This

word

contains

the

address

on

the

drum

of

the

physical

record

in

the

bottom

bits.

Three

operations

are

available

to

executive

programs

only.

They

are

intended

for

use

by

the

system

in

dealing

with

file

names and

executive

commands.

A

new

drum

file

with

a

new

index

block

can

be

created

by

BRS

1

with

an

index

block

number

of

0

in

A. The

file

number

is

returned

in

A as

usual

and

the

index

block

number

in

X.

The

initial

settings

of

the

r,

w,

and p

capabi~ities,

and

the

sequential

I/O

mode

flag,

should

be

given

in

B.

To

read

an

index

block

into

core

BRS

87

ma.y

be

used.

It

takes

the

address

of

the

block

in

A and

in

X

the

first

word

in

core

into

which

the

block

is

to

be

read.

9.2

other

Sequential

Files

9-7

In

addition

to

drum

sequential

files,

the

user

has

some

other

kinds

of

sequential

files

available

to

him. These

are

all

opened

with

the

same

ERS

1,

except

for

the

device

number.

Available

device

numbers

are

Paper

tape

input

1

Magtape

input

4

Magtape

output

5

PDP-5

link

input

6

PDP-5

link

output

7

The

device

number

is

put

into

X.

The

unit

number,

if

any,

is

put

into

A.

The

file

number

for

the

resulting

open

file

is

returned

in

A.

If

BRS

1

fails,

it

returns

an

error

condition

in

A

as

described

in

Section

9.1. Three

error

conditions

apply

to

magtape

only:

o Tape

not

ready

1 Tape

file

protected

(output

only)

2 Tape

reserved

(see

p.

9-8).

ERS

1

also

accepts

the

following

three

character

mnemonics

instead

of

the

device

numbers.

Either

the

name

or

the

number

goes

in

X

for

the

call.

1

PrI

2 PrO

3 eDI

4

MrI

5

MfO

6 PDI

7

PDQ

8 FSI

9

FSO

10 FIL

11

LPO

12

MDI

13

MOO

14

eSI

15

eso

16 TTl

17

TTO

18

NON

19

lOS

20

SNP

paper

tape

input

paper

tape

output

(not

available)

card

input

(not

available)*

mag

tape

input*

mag

tape

output*

PDl:5

input

PDl:5

output

drum

input*

drum

output*

drum

input

and

output*

line

printer

out

(not

available)*

direct

mag

tape

input*

direct

mag

tape

output*

controlling

teletype

input

controlling

teletype

output

specified

teletype

input

specified

teletype

output

nothing

subroutine

file

snooper

counters

(Berkeley

only)

*

requires

executive

status

9-8

ERS

1

is

inverted

by

ERS

110, which

takes

a

file

number

in

A and

returns

the

corresponding

device

name

in

X and

unit

number

in

A.

These

files

may

also

be

closed

and

read

or

written

in

the

same

manner

as

sequential

drum

files.

The magtape

is

only

available

to

executive·type

programs.

LDA

=1

(end

of

record)

eTRL

=file

number

is

available

for

physical

sequential

file

5 (magtape

output).

Several

other

controls

are

also

available

for

maptape

files

only.

These

are:

2

backspace

record

3

forward

space

file

4

backspace

file

5

write

three

inches

blank

tape

6

rewind

7

write

end

of

file

8

write

15

inches

blank

tape

These

controls

may

be

executed

only

by

executive

type

programs.

I/O

operations

to

the

magtape may,

of

course,

be

executed

by

user

programs

if

they

have

the

correct

file

number.

An

executive

program

may

arrogate

a

tape

unit

to

itself

by

putting

the

unit

number

in

A and

executing

BRS

118,

which

skips

if

the

tape

is

not

already

attached

to

some

other

job.

BRS

119

releases

a

tape

so

attached.

It

is

possible

for

magtape and

card

reader

files

to

set

9-9

the

error

bit

in

the

file

number. The

first

I/O

instruction

after

an

error

condition

will

read

the

first

word

of

the

next

record--the

remainder

of

the

record

causing

the

error

is

ignored.

The

magtape

routines

take

the

usual

corrective

procedures

when

they

see

hardware

error

flags,

and

Signal

errors

to

the

program

only

as

a

last

resort.

The phantom

user's

three

second

routine

checks

to

see

whether

a W-buffer

interrupt

has

been

pending

for

more

than

three

seconds.

If

so,

it

takes

drastic

and

ill-defined

action

to

clear

the

W-buffer.

BRS

114

also

takes

this

drastic

action;

it

can

be

used

if

a program

is

aware

that

the

W-buffer

is

malfunctioning.

Direct

tape

I/O pa.ckage. A mechanism

for

accessing

arbitrarily

formatted

mag

tape

is

available.

~he

appropriate

operations

are:

~Sl

~n

BRS

2

(or

17

or

2p)

close

BrO

block

input/output

CTRL

control

9-10

BIO

is

used

in

the

normal way,

with

a word

count

in

A and

core

address

in

X.

BIO

will

not

give

you more

data

than

specified

by

A.

In

no

case

may

the

block

requested

cross

a page boundary.

On

input,

BIO

will

skip

if

the

word

count

presented

is

exactly

right;

otherwise,

it

will

not

skip,

and

will

leave

the

number

of

words

actually

transferred

in

A and

the

next

core

address

in

X.

The

flag

bits

(EOR

and

EOF)

in

the

user's

file

number

are

set

as

with

the

normal

BIO

for

tapes.

In

addition

to

controls

3-8

for

tape

in

the

CTRL

operation,

CTRL

9 has been

~plemented

to

allow

the

user

to

set

the

mode

for

the

tape.

This

operation

takes

a ¢

or

1

in

B2l

for

setting

the

tape

in

odd

or

even

parity.

(TSS

tapes

use

odd

parity.)

B22

and

B23

contain

the

"frame

count,"

a

mysterious.

feature

of

the

W-buffer.

Use

one

less

than

the

number

of

6-bit

characters

per

word

to

be

shipped.

On

reading

the

characters

are

stored

right-justified

in

memory.

On

writing

they

are

taken

out

left-

justified.

The

word

count

for

transfers

covers

the

numbers

of

words

in

core

actually

used.

When

the

tape

1s

opened,

the

mode

is

set

to

odd

parity,

four

characters

per

word.

Snooper

Counters.

The

Berkeley

system

has

a

collection

of

hardware

counters

which

monitor

external

signals.

These

may

be opened

as

a

file

with

ERS

1.

In

addition,

two

operations

are

provided.

CTRL

fn

requires

a 1

in

A,

and

1/32

of

the

number

of

machine

cycles

to

be

monitored

in

B.

BIO

fn

reads

in

the

counters.

9-11

9.3

File

Control

Blocks

Every

open

file

in

the

system

has

associated

with

it

a

file

control

block.

This

block

consists

of

four

words

in

the

following

format:

FA

FW

FD

Fe

FB

Drum

files

only

0 2

first

index

block

address

or

0

0

subroutine

address

0 Cl 7i5 C2

15

16 C3

c D R R 0

H F X D U 0

device

0 T

0 0 0 0 0 0

0 2 9

char

3

job

8

number

drum

buffer

address

or

0

count

0 0

busy

count

(-1

if

file

not

busy)

Cn

= word

being

packed

or

unpacked

char

count

=

-1

to

2

CH

=

character

oriented

OUT

=

output

DF

=

drum

file

{

RX

= random

access

RD

=

read

only

ERR

:::

error

23

normal

file

subr.

files

normal

file

subr.

file

9.4 PermanentlY Open

Files

There

are

a few

built-in

sequential

files

with

fixed

file

numbers:

o

controlling

teletype

input

1

2

looo+n

2000-+n

controlling

teletype

output

nothing

(discard

all

output)

input

from

teletype

n

output

to

teletype

n

These

files

cannot

be opened and need

not

be

closed.

10-1

10.0

Random

Drum

Files

A random drum

file

is

identical

in

physical

structure

on

the

drum

to

a

sequential

drum

file.

The

only

major

difference

is

that

the

non-zero

words

of

the

index

block

are

not

necessarily

compact.

Th~

reason

for

this

is

that

information

is

extracted

from

or

written

into

a random

file

by

addressing

the

specific

word

or

block

of

words which

is

desired.

From

the

address

which

the

user

supplies,

the

system

extracts

a

physical

block

number

by

dividing

by

the

data

block

size

and a

location

of

the

word

within

the

block

which

is

the

remainder

of

this

diviSion.

Further

division

by

144

yields

the

appropriate

index

block.

A

file

may

have any number

of

index

blocks.

A random

file

may

be opened by

using

BRS

1

with

a

device

number

of

10.

No

distinction

is

made

between

input

and

output

to

a random drum

file.

A random

file

may

also

be

closed

by

BRS

2,

like

any

sequential

file,

and CIO,

WIO,

and

BIO

may

be

used

for

input-output

to

random

files.

The

sequential

Ilo

mode

(input

or

output)

is

controlled

with

BRS

143

and 144.

The

following

additional

operations

are

available:

To

read

a word from a random

file,

execute

the

instructions

LDB

=address

DWI

=file

number

The

word

is

returned

in

A.

To

write

a word on a random

file,

put

the

word

in

A and

execute

the

instructions:

LDB

=address

DWO

=file

number

Block

input-output

to

random

files

is

also

possible.

To

input

a

block,

execute

the

instructions:

LDX

=first

word

address

LOA

=number

of

words

LDB

=first

address

in

file

DBI

=file

number

To

output

a

block

of

words

to

a random

file,

execute

the

instruction

DBO

=file

number

10-2

with

the

same

parameters

in

the

central

registers.

These

block

input-output

operations

are

done

directly

to

and from

the

user's

memory,

as

is

BIO.

Drum

buffers

are

not

involved

and

the

operation

can

go

very

quickly.

It

is

possible

to

define

a random

file

which

has

been

previously

opened

as

the

secondary

memory

file.

To

do

this,

execute

the

instructions

LilA

=file

number

BRS

58

The

specified

file

remains

the

secondary

file

until

another

secondary

memory

file

is

defined

or

until

the

file

is

closed.

To

access

information

in

the

secondary

memory,

two

SYSPOPs

are

provided.

These

POPs

work

exactly

like

DWI

and

DWO

except

that

they

take

the

drum

address

from

memory

instead

of

requiring

it

to

be

in

B.

To

read

a word

of

secondary

memory

into

the

A

register,

the

instruction

LAS

address

should

be

executed.

To

store

a word from A

into

the

secondary

memory,

the

instruction

SAS

address

should

be

executed.

The

word

addressed

by

either

one

of

these

SYSPOPs

should

contain

the

drum

address

which

is

to

be

referenced.

This

word

may

also

have

the

index

bit

set,

in

which

case

the

contents

of

the

index

register

will

be added

to

the

contents

of

the

word

to

form

the

effective

address

which

is

actually

used

to

perform

the

input-output

operation.

The

mechanism

for

acquiring

and

releasing

random drum

file

space

is

very

s~ilar

to

the

mechanism

for

allocation

of

core

memory. Whenever

the

user

addresses

a

section

of

a random

drum

file

which he

has

not

previously

used,

the

necessary

blocks

are

created

and

cleared

to

O.

Note

that

the

user

should

avoid

unnecessarily

large

random drum

addresses,

since

they

may

result

in

the

creation

of

an

unnecessary

number

of

index

blocks.

To

release

random

drum

memory,

use

BRS

144.

10-3

10.1

Direct

Drum Access

An

even

more

efficient

method

of

acceSSing

information

on

the

drum

is

provided

by

an

interface

Which

alloys

the

user

to

acquire

2K

pages on

the

drum

and

read

or

write

on

them

directly.

This

space

is

ass

igned

fran

the

swapping

area

on

the

drum

and

referred

to

directly

by

its

drum

address;

a

bit

table

private

to

the

user

is

used

for

validity

checking.

To

acquire

a

2K

page,

execute

BRS

126

with

the

desired

angular

position

on

the

drum

of

the

page

to

be

assigned

in

the

bottom

bits

of

A.

If

no

more

space

is

available,

BRS

126

returns

without

skipping.

otherwise,

BRS

126

skips

and

returns,

in

A,

the

drum

address

of

a

2K

page

as

a word

address

(i.e.,

with

the

bottom 11

bits

zero).

A page

may

be

released

by

putting

this

address

in

A and performing

BRS

1~.

To

release

~

pages

acquired

in

this

manner,

execute

CLA

BRS

7.

This

is

done

automatically

by

the

RESET

cClllllland

in

the

executive,

as

well

as

by

RECOVER

and

by

a

call

for

a

new

subsystem.

It

should be

noted

that

DUMP

does

~

preserve

pages

acquired

by

,BRS

126.

To

read

or

write

on a page

acquired

with

BRS

126,

use

LDA =core

address

LDB

=drum

address

LDX

=word

count

bS

124

to

readJ-

BRS

125

to

write

10.4

These BRS's

preserve

all

the

central

registers

and normally

skip.

A

no-skip

return

indicates

an

uncorrectable

transmission

error.

The

following

restrictions

are

checked by

the

monitor and

will

result

in

an

illegal

instruction

trap

if

violated:

1)

The

drum

address

must be a

multiple

of

256

(decimal)

and

lie

within

some

page

assigned

to

the

user

via

BRS

126.

(The

latter

restriction

does

not

apply

to

executive

programs.)

2)

The

transfer

must

not

cross

a

2K

page boundary

either

in

core

or

on

the

drum.

3)

It

is

illegal

to

attempt

to

read

into

a

read-only

page

with

BRS

124

(this

produces a

memory

trap

if

violated).

11-1

11.0

Subroutine

Files

An

addition

to

the

above-mentioned

machinery

for

performing

input-output

through

physical

files,

a

facility

is

provided

in

the

system

for

making a

subroutine

call

appear

to

be an

input-

output

request.

This

facility

makes

it

possible

to

write

a

program which does

input-output

from a

file

and

later

to

cause

further

processing

to

be

performed

before

the

actual

input-

output

is

done,

simply

by

changing

the

file

from a

physical

to

a

subroutine

file.

A

subroutine

file

is

opened

by

executing

the

instructions

LOX

parameter

word +

subroutine

address

BRS

1

This

instruction

skips

or

returns

an

error

code,

as

for

sequential

files.

The

opcode

field

of

the

parameter

word

indicates

the

characteristics

of

the

file.

It

may

be

one

of

the

following

combinations:

11000000

1ll0ooo0

01000000

01100000

CharOacter

input

subroutine

Character

output

subroutine

Word

input

subroutine

Word

output

subroutine

I/O

to

the

file

may

be

done

with

CIO

or

WIO,

regardless

of

whether

it

is

a word

or

a

character-oriented

subroutine.

The

system

will

take

care

of

the

necessary

packing

and

unpacking

of

characters.

BIO

is

also

acceptable.

The

opening

of

a

subroutine

file

does

nothing

except

to

create

a

file

control

block

and

return

a

file

number

in

the

A

register.

When

an

I/O

operation

on

the

file

is

performed,

the

subroutine

will

be

called.

This

is

done

by

s~ulating

run

SBRM

to

the

location

given

in

the

address

field

of

the

X

register

given

to

the

BRS

1 which opened

the

file.

The

contents

of

the

B and X

registers

are

transmitted

from

the

I/O Syspop

to

the

subroutine

unchanged.

The

contents

of

the

A

register

may

be

changed

by

the

packing

and

unpacking

operations

necessary

to

convert

from

character-oriented

to

word-oriented

operations

or

vice

versa.

The

I/O

subroutine

may

do

an

arbitrary

amount

of

11-2

computation

any

may

calIon

any

number

of

other

I/O

devices

or

other

I/O

subroutines.

A

subroutine

file

should

not

call

itself

recursively.

When

the

subroutine

is

ready

to

return,

it

should

execute

BRS

41.

This

operation

replaces

the

SBRR

which would

normally

be

used

to

return

from a

subroutine

call.

The

contents

of

B

and X when

the

BRS

41

is

executed

are

transmitted

unchanged buck

to

the

calling

program. The

contents

of

A

may

be

altered

by

packing

and

unpacking

operations.

A

subroutine

file

is

closed

with

BRS

2

like

any

other

file.

In

order

to

implement

BRS

41,

it

is

necessary

to

keep

track

of

which I/O

subroutine

is

open.

This

information

is

kept

in

six

bits

of

the

PAC

table.

The

contents

of

these

six

bits

is

transferred

into

the

opcode

field

of

the

return

address

when an

I/O

subroutine

is

called,

and

is

recovered

from

there

when

the

BRS

41

is

executed.

The

user

should

be

warned

that

a

subroutine

file

should

not

be

used

by

a progrrum

in

a

different

address

space

from

the

subroutine

itself.

In

particular,

subroutine

files

may

not

be

given

to

the

BRSs

which

involve

acccess

to

nwned

files

(described

in

the

next

section).

12-1

12.0

File

Naming System

Because

of

the

possible

conrlicts

which

may

arise

when

several

users

are

s~ultaneously

trying

to

access

the

same

peripheral

device,

such

devices

cannot

be

handled

directly

by

users

at

the

level

offered

by

BRS

1

--

which

is

available

only

to

programs

with

executive

status.

At

the

user

level,

storage

devices

can

only

be

referenced

in

an

indirect

manner,

by

writing

or

reading

a

"file."

Files

are

the

primary

means

by

which

the

user

establishes

continuity

between

one computer

run

and

the

next.

A

file

is

any

named

block

of

information

which

the

user

finds

it

convenient

to

regard

as

a

single

entity;

the

commonest example

of

a

file

is

a

program.

To

provide

a

check

against

inappropriate

use,

files

created

by

the

Exec and

TSS

subsystems

are

classified,

according

to

the

nature

of

the

information

in

them,

into

one

of

four

types,

numbered I

to

4.

This

type

number

is

carried

along

with

the

information

content

and

may

be

checked

whenever

the

file

is

referenced.

The

file

types

are:

1.

Core Image -

The

information

in

this

originates

from

specified

segments

of

core

memory.

2.

Binary

3. Symbolic

4.

Dump

-

The

information

has

the

form

of

an

assembled,

but

unloaded

program.

-

The

informa.t

ion

is

of

a

form.

which can be

readily

listed

on

some

printing

device.

-Comprises

all

the

information

in

memory

necessary

to

restart

the

user

from

his

current

situation,

i.e.,

the

situation

at

the

time

of

creation

of

the

dump

file.

Symbolic

information

may

come

directly

from

paper

tape

or

teletype.

These

devices

may

be

referenced

as

type

3

files

by

using

the

name

of

the

corresponding

physical

medium,

viz.

-

PAPER

TAPE

TELETYPE

12-2

These names

are

built

into

the

system

and

are

always

appropriately

recognized.

Another

built-in

file

name

is

NOTHING

which always

contains

precisely

nothing

and whose

function

is

to

act

as

an

infinite

sink

in

which

limitless

unwanted

output

can

be

lost.

A

commoner

source

for

symbolic

files

is

the

output

from

some

subsystems,

notably

the

text

editor,

QED.

Type

2,

binary

files

normal~y

arise

as

the

output

from

the

machine-language

a,ssembler ARPAS.

Until

the

actual

process

of

output

from

the

subsystem

occurs,

identification

of

the

information

is

handled

by

the

subsystem

and

is

usually

implicit

since

the

subsystems

can

handle

only

one

file

at

a

time.

However,

when

the

information

is

ejected

into

a

context

involving

many

other

blocks

of

information

of

a

similar

kind,

some

explicit

identification

must be

attached

to

it.

12.1

File

Naming

The

names which

the

user

is

free

to

invent

and

assign

to

files

are

of

two

types:

1.

Permanent

name

s

2.

Scratch

names

Scratch

names

differ

from permanent names

in

that

they

and

the

files

associated

with

them

are

lost

when

the

user

leaves

the

system,

USing

the

LOGOUT

command;

they

are

otherwise

treated

identically.

A permanent

name

is

an

arbitrary

string

of

characters

not

beginning

with

/

or:.

A

scratch

name

is

an

arbitrary

string

of

characters

beginning

with

/

or:.

To

those

users

who

have drum

file

privileges,

a /

identifies

a

drum

file,

: a

disk

file.

As

permanent names

we

have -

ABC

PROGRAM

1

124

while

as

scratch

names

we

have -

/ABC

:421/

12-3

Any

permanent

or

scratch

file

name

may

be

quoted

by

surrounding

it

with

single

quote

marks.

Thus,

'ABC'

and

'/001/'

are

quoted

file

names. The

quoted

name

refers

to

exactly

the

same

file

as

the

unquoted

one;

it

differs

only

in

the

way

it

is

recognized

by

the

exec.

Control

A

(backspace)

is

legal

on any

name

being

typed

to

the

file

system

unless

command

recognition

is

taking

place.

When

reference

is

made

to

an

unquoted

name,

the

exec

will

anticipate

the

user

and

consider

the

name

to

be

fully

delivered

as

soon

as

it

has

received

sufficient

characters

to

distinguish

the

name

from

all

others

currently

defined

by

the

user.

This

means

that

a

new

name

can

~

be

introduced

in

its

unquoted

form. A

quoted

name, on

the

other

hand,

is

always

accepted

in

its

entirety

from

the

user.

The

initial

and

terminal

quotes

are

then

removed

and

the

name

compared

with

the

directory

of

nwmes

currently

defined

by

the

user.

If

it

matches one

of

them,

it

is

taken

to

refer

to

that

file,

just

as

though

it

had

been

presented

in

unquoted

form.

If

it

is

new, however,

it

will

normally

give

rise

to

an

error

message

unless

it

appears

in

one

of

the

following

contexts:

a)

In

the

DEFINE

NAME

command

(c.f.

Doc. R-22,

Section

5.5)

b)

As

an

output

file

name,

in

which

case

a

new

file

with

the

specified

name

will

be

created

to

hold

the

output.

For

example,

let

XYZ

be

the

name

of

an

existing

file

and

/123

be a new

unattached

file

name. Then

the

exec

command

~Opy

XYZ

TO

'/123'.

has

the

effect

of

creating

a new

scratch

file,

called

/123,

having

the

same

information

content

as

XYZ.

If

/123

is,

however,

already

attached

to

some

existing

file,

then

the

information

content

of

that

file

is

replaced

by

that

of

XYZ.

In

summary,

it

will

be

seen

that

the

exec's

file

name

recognition

apparatus

works

in

two ways,

depending

essentially

on

whether

the

name

is

quoted

or

not.

Quoted names must always

be

given

in

entirety;

the

exec

waits

for

the

terminating

quote

before

attempting

to

recognize

the

name. Unquoted names

are

anticipated;

the

exec

recognizes

or

rejects

them

as

soon

as

it

can,

inSisting

that

they

match

some

name

already

in

the

user's

directory

of

file

names. Note

tha.t

the

BEGINNER,

NOVICE

and

EXPERT

commands

apply

to

file

name

recognition

(see

R-22,Section

5.7).

12-4

12.2

Accessing

Other

Users'

Files,

Special

Groups

The naming

system

described

is

adequate

to

reference

all

the

files

belonging

to

the

current

user,

in

whose

name

the

exec

was

entered.

However,

to

refer

to

files

belonging

to

another

user,

it

is

possible

to

augment

the

file

name

by

that

user's

name

together

with,

optionally,

a

special

accessing

code

called

the~~.

or

To

do

this

the

basic

file

name

must

be

prefixed

by

one

of:

( <

user

name

> )

( <

user

name

>,

<

group

name

> )

Thus

for

example:

(JONES)

'FIIEl'

or

(JONES,GROUP1)

'FILE1'

When

such

a

string

as

the

last

is

collected

from a

teletype

by

BRS

15

or

16,

the

characters

II,

GROUPl"

are

not

echoed

to

the

teletype

so

that

the

secrecy

of

the

special

group

name

is

preserved.

The

access

that

any

other

user

may

have

to

each

of

Jones'

files

is

in

the

hands

of

Jones

.himself.

Jones

may

declare

that

a

member

of

the

public

at

large

who

tries

to

access

his

'FILEl'

using

(JONES)'FII£l'

has

entire

(read-write)

access,

read-only

access,

or

no

access

at

all.

It

is

also

open

to

Jones

to

define

independently

a

greater

degree

of

accessibility

to

a

user

who

supplies

the

group

name.

Special

groups

can

be

created

by

BRS

61

and

the

command

SET

MODES

FOR

FILE

(R-22,

Section

5.5)

or

deleted

by

BRS

62

and

the

same command.

ERS

61

-

Define

Special

Group

Takes a

string

pointer

in

AB.

The

string

is

an

arbitrary

string

of

characters

and

is

taken

to

define

a

new

special-group

name. The

BRS

assoctates

with

it

a

number,

n,

in

the

range

IS

~

15, which

it

skip

returns

in

A.

A

file

may

then

be

placed

in

that

special

group

by

setting

this

number

in

the

appropriate

bits

of

the

file

mode

word

(see

BRS

48).

A

user

may

have up

to

15

currently

defined,

distinct

special

groups;

an

attempt

to

define

more

results

in

a no

skip

return

with

A=O.

An

attempt

to

define

an

already

existing

special

group

name

also

results

in

a

no

skip

return,

but

with

the

group

number

in

A.

12-5

BRS

62

-

Delete

Special

Group

Takes a

special

group

number

in

A.

The

associated

special

group

name

is

deleted

and

the

number

made

available

for

reassignment

to

a

new

name.

All

files

belonging

to

the

special

group

are

released

from

it.

If

no

name

is

attached

to

the

number,

the

BRS

has

no

effect.

12 . 3 Pseudonyms

By

means

of

the

command

USE

NAME

it

is

possible

for

a

user

to

insert

in

his

file

directory

a pseudonym,

that

is,

a

name

which,

instead

of

being

a

tag

for

a

real

file,

is

a

tag

for

another

name

possibly

including

a

user

name

and

group

name.

If

he

later

uses

the

pseudonym,

the

action

taken

is

exactly

the

same

as

if

he

had

typed

the

entire

name

for

which

the

pseudonym

stands.

12.

t~

Doing r/o

to

Files,

File

Numbers

The

file

name

is

an

unwieldy

and

inconvenient

handle

for

the

I/O

routines

to

use

in

transferring

data.

These

routines

instead

reference

the

file

by

a compact,

I-word

file

number

which

is

more

closely

related

to

the

file's

whereabouts.

Thus

system

subroutines.

are

provided

to

assign

to

a

given

file

name

some

temporary

file

number.

The

user

may

find

it

useful

to

remember

that

the

system

subroutines

which

perform

information

transfers

to

and from

sequential

files

are

the

same

for

input

as

for

output.

The

distinction

is

carried

by

the

file

number

with

which

they

are

used--whose

character

is

in

turn

determined

by

whether

it

was

returned

by

BRS

15

(input)

or

BRS

16

(output).

Hence a program

which

was

designed

to

output

information

can,

without

ill-effect,

be

delivered

an

input

file

number. The

effect

will

be

to

lose

the

characters

\'Thich

the

program would be

trying

to

output,

while

taking

in

characters

in

their

place--these

too,

due

to

the

nature

of

the

program,

will

in

general

be

ignored

and

lost.

Names

are

recognized

and a

file

number

provided,

if

required,

by

the

system

subroutines

BRS

15, 16;

they

may

be

deleted

by

12-6.

ERS

63.

The

preceding

description

of

the

manner

in

which

file

names

are

recognized

largely

assumes

that

they

are

being

typed

in

on a

teletype.

They may, however,

be

presented

to

the

BRS'

s

as

a ready-made

string

of

characters

in

core.

Entry

parameters

for

the

BRSs

include

a

string

pointer

to

a

string

in

core

together

with

an

input-file

number (most commonly

teletype).

The

character,

string

may

be

null

or

an

initial

part

of

a

file

name

or

an

entire

file

name.

In

the

first

two

cases

sufficient

characters

are

appended from

the

input

file

to

ensure

recognition

or

rejection

of

the

name.

[A

Remark on

"Random"

Files

on Tape

Random

and

sequential

files

may

be

stored

and

accessed

with

equal

facility

on "random"

storage

devices,

such

as

the

drum

and

disk.

On

the

other

hand

sequential

devices,

such

as

magnetic

or

paper

tape,

cannot

be

conveniently

or

efficiently

accessed

in

the

manner

of

random

files

and

are

restricted

to

holding

only

sequential

files.

However,

the

command

'COPY

FILE'

will

allow

a

user

to

copy

information

from

an

existing

random

file,

say

on

the

drum,

to

a

sequential

but

has

a

special

format

which does

not

allow

it

a

sensible

interpretation

as

a

sequential

file

but

permits

the

original

random

format

to

be

restored

when

it

is

copied

back

to

a random

device.

Such a "random

tf

file

on a

sequential

medium

will

result

in

the

return

of

the

apparently

paradoxical

information,

1-0

in

bits

0,1

of

X when

the

file

is

opened

by

BRS

15,

16.

Before

accessing

information

in

such a

file

the

user

should

copy

it

(using

the

Exec

command

or

BRS

92)

to

a

non-sequential

medium.]

12.5

Qpening

Input

Files

BRS

15 -

Open

named

file

for

input:

Takes

in

A a

control

word

in

B

the

address

of

a

string

pointer,

or

~

in

X a

dual

file

number.

The

function

of

this

BRS

is

to

recognize

an

existing

file

name,

optionally,

open

the

file

for

input

and

return

a

file

number

for

use

with

subsequent

data-input

commands.

12-7

Designation

of

the

File

The

string

addressed

by

B must be

the

complete

or

incomplete

name

of

a

predefined

file.

If

the

name

is

incomplete,

characters

will

be appended from

the

input

file

whose number

is

given

in

the

least

significant

12

bits

of

X

--

until

sufficient

characters

are

available

to

detennine

uniquely

a

file

name

(or

no such name).

If

the

file

name

is

unquoted

so

that

prerecognition

occurs,

the

"tail"

of

the

name

is

echoed

back

to

the

output

file

whose number

is

given

in

the

most

significant

12

bits

of

X.

If

B=O

on

entry

a

null

string

is

assumed and

characters

collected

from

the

input

file

are

not

transmitted

to

the

caller's

memory.

If

bit

a

of

B

is

set,

the

string

delivered

is

considered

null--its

position

being

defined

by

the

first

word

of

the

string

pointer.

Unless

B=O

on

entry

the

completed

or,

in

the

case

of

non-recognition,

partially

completed

file

name

will

be

transmitted

to

the

caller's

memory.

If

a pseudonym was

delivered,

it

will

be

replaced

by

the

string

for

which

it

stands.

Unless

the

file

name

·was

complete on

entry

(i.e.,

no

charac-

ters

need

be

taken

from

the

input

file),

a

tenninating

character

must be

delivered

to

confirm

or

abort

the

file

name. Confirming

characters

are

those

with

an

internal

code

representation

0

to

16

8,

also

semicolon,

tab,

line

feed

and

carriage

return;

the

aborting

character

is

7.

All

other

characters

cause

7

to

be

output

and

are

other\vise

ignored.

Action:

This

is

dependent on

options

which

are

specified

by

bits

1

and 2

of

A on

entry.

These

are:

Bit

1,

if

set,

$uppresses

opening

the

file

(no

file

number

is

returned)

Bit

2,

if

set,

suppresses

the

need

for

a

terminating

character;

when

these

bits

are

not

set,

the

action

is

as

follows:

If

the

name

is

recognized

and a

valid

terminating

character

is

received,

the

file

is

opened

for

input.

There

is

a

skip

return

with

In

A,

a

file

number

In

B,

the

terminating

character

In

X,

is

a composite word

comprising

1.

TAPE

or

PERMANENT

FILES

WORD

a

WORD

1

WORD

2

WORD

3

Mask

for

BRS

48

SR

=

sequential

or

random

W?1

PRA

=

private

accessibility

PUA

=

public

accessibility

1 = random

1 =

read

only

o =

denied

to

public

1 =

public

read

only

2 =

public

read

and

write

SGA

=

special

group

accessibility

a =

read

and

write

SGN

=

special

group number

1 =

read

only

o = none

S =

status

U = unused

o =

file

permanently

on

drum

1 =

file

on

drum

2 =

file

on system

tape

3 =

file

on

private

tape

2.

SCRATCH

FILES

WORD

1 =

-1

WORD

0 =

0,

WORDS

2,3

as

for

TAPE

FILES

3. BUILT-

IN

FILES

WORD

3 =

-2;

WORD

2 = 0

a.

Device

WORD

0 = 0

WORD

1 (9

to

11]

= no.

of

tape

unit

WORD

1 [12

to

17] =

device

no (O/p)

WORD

1 [18

to

23] =

device

no. (lip)

12A-l

b.

Permanent

file

no.

WORD

0 f 0

4. SPECIAL

GROUPS

WORD

2 =

-1

WORn

1 (6

to

11] =

file

no.

(O/P)

WORn

1 [18

to

23]

=

file

no. (rip)

12A-2

WORD

0 = 0

WORD

1 =

creation

date

WORD

3

[20

to

23]

--

5 .

PSEUDONYMS

WORD

3 =

-1

group

no.

WORDS

0,1

=

string

pointer

to

real

string

WORD

2 = 0

Description

Block Format

(A)

12A-3

FILE

DIRECTORY

DESCRIPTION

PREAMBLE

AND

STORAGE

ARRANGEMENTS

0

FLTH

ZRO

File

directory

length

1

eFTA

ZRO

Address

of

compressed

file

input

table

(eFIT)

2

SGUS

ZRO

(Bits

set

to

indicate

special

group numbers

in

use)

3

FDIX

SRO

Drum

index

block

address

for

this

file

directory

4

FUNO

ZRO

User number

5

BSS

ZRO

Address

of

beginning

of

description

block

storage

6

HTL

ZRO

Beginning

of

hash

table

(BRS

5,6

table)

II,

EHTL

ZRO

End

of

hash

table

On.S

r,

IoVQItt)

1,

FDSS

ZRO

Character

address

of

beginning

of

string

storage

(WCH

table)

12

EFDSS

ZRO

End

of

string

storage

13

ZRO

Garbage

collection

option

The

remaining

parts

of

the

file

directory

appear

in

the

following

order:

Hash

table

(HTL,

EHTL)

String

storage

(EHTL,

BSS)

File

description

block

storage

(BSS,

eFTA)

l2A-4

USER

DIRECTORY

DESCRIPTION

(A)

PREAMBLE

AND

STORAGE

ARRANGEMENTS

0

BURT

ZRO

Beginning

of

hash

table

(BRS

5,6

table)

1

EUHT

ZRO

End

of

hash

table

2

ZRO

BRS

5,6

link

3

BUDSS

ZRO

Character

address

of

beginning

of

string

storage

(WCH

table)

4

EUDSS

ZRO

End

of

string

storage

5

ZRO

Garbage

collection

option

6

BUDBT

ZRO

Address

of

beginning

of

description

block

table

7

BUDB

ZRO

Length

of

each

user

description

block

The

remainder

of

the

directory

appears

in

the

following

order:

Hash

table

(BUHl',·

EUHT)

String

storage

(EUHT,

BUDBT)

User

description

blocks

(BUDBT,

end

of

directory)

(B)

TYPICAL

HASH

TABLE

ENTRY

~2~

______________________

S_TR

__

IN_G

__

~_S_~

__

~

___

TO

____________

~

.

USER

NUMBER

(c)

TYPICAL

DESCRIPI'ION

BLOCK

ENTRY

0

HTA

ZRO

Address

of

hash

table

entry

1

FDL

ZRO

File

directory

drum

address

2

DA

ZRO

Maximum.

drum

block

allowance

3

AW

ZRO

Access word

4

PW

ZRO

Password hash code

5

CTW

ZRO

CPU

time word

(6oths

of

a second)

6

LTW

ZRO

LOGIN

time word (seconds)

l2A-5

ACCESS

BITS

ARE

0

WAr!'

}

1

IDIOT

BRS

37

mode

2

PRFFLG

permanent

file

flag

3

XMOK

exec

mode

OK

4

NTFFLG

new

tape

file

flag

5

UTTFLG

new

files

to

user

tape

6 OPI'FLG

operator

flag

In

bits

6

to

23,

the

file

length

In

bits

3

to

5,

the

file

type

Bit

0

is

set

if

the

file

is

random

Bit

1

is

set

if

the

file

is

not

stored

on a

sequential

medium.

Error

Conditions

12-8

All

error

conditions

are

followed

by

a

no-skip

return

with

an

indicator

in

X;

A and B

are

undisturbed.

-5~~-1

shows

that

the

file

could

not

be opened.

The

possible

reasons

correspond

one-one

with

those

associated

with

a

no-skip

return

from

BRS

1

with

-2~~2

(see

pp.

9-1, 9-7).

X=l

This

exit

occurs

if

the

name

given

is

not

a

predefined

name

in

the

specified

user's

file

directory.

X=2

Indicates

that

the

file

name

was

aborted

by

delivering

?

as

a

terminating

character.

X=O

Any

such

error

is

accompanied

by

one

of

the

following

'error

messages'

being

sent

to

the

command

output

file

(normally

the

teletype).

?

ILLEGAL

USE

OF

PSEUDONYM

-NOT

PUBLIC

-NO

GROUP

NAHE

ATTACHED

-VlRONG

GROUP

NAME

When

the

requested

file

exists

on

magnetic

tape

it

is

possible

to

receive

about

20

different

error

messages,

most

of

which

are

self

explanatory.

The

pcs

ition

check

message,

"(

~:

n)"

means

only

that

the

tape

has

reset

its

position

after

becoming

"lost"

and

should

be

of

no

concern.

12.6

Opening

Output

Files

BRS

16 -

Open

named

file

for

output

Takes

in

A a

control

word

In

B

the

address

of

a

string

pointer,

or

~

In

X a

dual

file

number.

This

BRS

is

provided

to

read

an

existing

or

new

file

name

and,

optionally,

open

the

file

for

output

and

return

a

file

number

for

use

with

subsequent

data-output

instructions.

Designation

of

the

File

The

file

name

is

obtained

from B and X

in

exactly

the

manner

of

BRS

15

(q.v.)

except

that

if

the

name

is

enclosed

between

quotes

and

is

not

delivered

in

association

with

some

other

user's

name,

then

it

may

be new.

Action

12-9

This

is

again

dependent on

the

control

word

in

A,

on

entry.

Bit

0,

according

as

it

is

°

or

1,

specifies

that

the

file

to

be

created

is

sequential

or

random.

Bit

1

is

normally

zero,

to

indicate

that

the

specified

file

should

be opened and a

file

number

returned

in

A.

If

the

user

does

not

wish

to

open

the

file

this

bit

should

be

set.

Bit

2

if

set

suppresses

the

need

for

a

terminating

character.

It

also

suppresses

output

of

the

message

OLD

FILE

or

NEW

FILE,

which

is

normally

produced

after

identification

of

a

quoted

file

name.

Bits

3

to

5 =

t,

indicate

the

file

type.

The

type

of

a

new

file

is

always

set

to

be

t.

The

type

of

an

old

file

is

changed

to

t

unless

t=O,

when

the

old

file

type

is

retained.

An

attempt

to

open

the

teletype

as

anything

but

a

type

3

file

is

an

error.

Bits

6

to

23

= S,

significant

only

for

tape

files.

S

is

taken

to

be

the

number

of

words

of

information

about

to

be

written.

If

a

new

tape

file

is

specified,

a space

of

3/2 S

words

is

reserved

after

the

current

last

file

on

tape.

For an

old

tape

file,

S

is

compared

with

the

amount

of

tape

space

currently

reserved

for

the

file.

If

it

is

greater,

an

error

message -

TOO

SHORT

is

produced,

followed

by

a

no-skip

exit;

the

file

is

not

opened.

The

normal

return

from

the

BRS

is

with

a

skip,

the

same

parameters

being

returned

in

A,

B and X

as

for

BRS

15

viz.

in

A a

file

number number

(if

opened)

in

B

the

terminating

character

(if

delivered)

in

X a composite word

comprising

the

file

length,

type

and

logical

structure

(random

or

sequential)--See

BRS

15.

Error

Conditions

R-21

12-10

All

error

conditions

are

followed

by

a

no-skip

return

with

an

indicator

in

X;

A and B

are

undisturbed.

-5~~-1

shows

that

the

specified

file

could

not

be

opened.

The

possible

reasons

correspond

one-one

with

those

associated

with

a

no-skip

return

from

BRS

I

with

-~~2

(see

pp.9-1,

9-7).

X=O

This

exit

follows

the

printing

of

one

of

the

following

error

messages on

the

command

output

file

(in

addition

to

the

possible

messages

given

for

BRS

15):

READ

ONLY

WRONG

TYPE

FILE

TOO

SHORT

FILE

DIRECTORY

FULL

X=l

if

the

file

name

is

new

and

either

unquoted

or

is

delivered

in

association

with

the

name

of

another

user.

X=2

if

the

abort

terminator

(?)

is

delivered.

Notes:

1)

Although

new

tape

files

for

the

ordinary

user

will

be

created

on

the

standard

user's

tape,

same

users

can

specify

the

tape

on which a

new

file

is

to

be

created.

For

such

users

a message

TAPE

SYS.

NO.

=

is

printed

and

a

decimal

number must

here

be

delivered

through

the

command-input medium.

2)

If

the

file

name

is

quoted

and

not

built

in,

one

of

the

messages

OLD

FILE

or

NEW

FILE

is

sent

to

the

command

output

medium.

As

described

above,

this

message

may

be

suppressed

by

setting

bit

2

of

A on

entry.

3)

An

attempt

to

change

the

logical

structure

of

an

old

file

(from random

to

sequential

or

vice

versa)

will

elicit

a

message

to

notify

the

user

before

the

name

terminator

is

delivered.

12.7

Miscellaneous

File

Operations

ERS

63

-

Delete

name

from

file

dire~tory

Takes

in

B a

string

pointer

in

X a

dual

file

number

12-11

The

entry

parameters

are

used

to

designate

a

name

in

the

file

directory

in

the

manner

of

BRS

15.

The

name

is

removed

from

the

directory

subject

to

the

following

conditions:

A

built-in

file

cannot

be

deleted.

The

BRS

will,

however,

allow

the

user

to

delete

all

its

names

except

the

last.

When

a pseudonym

is

delivered

to

the

BRS

the

pseudonym

itself

is

lost.

When

the

last

name

of

a

file

is

deleted,

the

file's

contents

are

also

lost.

A

successful

deletion

is

followed

by

a

skip

return.

A

no-skip

return

indicates

that

the

attempt

to

delete

failed.

The

contents

of

X

will

indicate

the

reason

for

failure

as

follows:

X=3,-2,-1

correspond

to

no-skip

returns

from

BRS

1

with

A=-2,

-1,0

re

spect

i ve

ly

. Such

an

exit

results

only

from

an

attempt

to

delete

a drum

:file.

X=O

indicates

an

attempt

to

delete

the

last

name

a

built-in

file.

X=l

if

the

name

is

not

in

the

file

directory.

BRS

60

-

Interrogate

file

description

block

Takes

in

B

the

address

of

a

string

pointer

in

X a

dual

file

number

of

The

entry

data

are

used,

in

the

manner

of

BRS

15,

to

determine

a

file.

The

first

three

words

of

the

description

block

for

that

file

(see

p.

l2A)

are

Skip-returned

in

A,

B and X

respectively.

BRS

48

-

Set

file

modes

Takes

in

A a

file

mode

word

in

B a

string

pointer

address

in

X a

dual

file

number.

B and X

are

used,

in

the

manner

of

BRS

15,

to

determine

a

file

name.

BRS

48

will

then

use

the

information

in

A

to

set

or

change

the

special

group membership,

type

and

accessibility

of

the

specified

file

(which must

belong

to

the

caller).

All

of

these

characteristics

are

determined

by

bits

1

to

4, and

6

to

16

of

the

third,

"mode", word

of

the

description

block

12-12

associated

with

the

file

(see

p.

l2A).

BRS

48

directly

replaces

these

bits

by

the

corresponding

bits

of

A

after

checking

A

for

consistency

and

existence

of

the

specified

special

group.

A

successful

mode

change

is

denoted

by

&

skip

return,

failure

by

a

return

without

skipping.

12.8 Opening

Scratch

Files

Scratch

files

are

all

kept

on

the

drum. They

differ

from

ordinary

files

in

that

they

disappear

completely

when

the

user

who

created

them

logs

out.

A

fixed

amount

of

drum

space

is

available

to

each

user

for

scratch

files,

which he

may

allocate

as

he

sees

fit.

If

he

attempts

to

exceed

the

allocation

a message

will

be

given.

A

scratch

file

may

be

created

by

BRS

16

or

any

of

the

commands

which

create

a

new

file,

by

delivering

to

them a

new

scratch

name

(see

12.1).

Alternatively,

for

a

scratch

file

with

a

name

of

the

form

/ddd/

where d

is

any

decimal

digit,

the

elaborate

string

delivery

and

recognition

procedure

of

BRS's 15,16,63

can

be

bypassed

by

using

BRS's 18,19,65

respectively.

Instead

of

a

string

~ointer

and

dual

file

number,

these

three

BRSs

take,

for

file

identification,

an

integer

in

X.

The

decimal

equivalent

of

this

number

is

a

string

of

three

digits

enclosed

between

slashes

is

then

used

as

a

file

name

to

refer

to

the

file

in

the

conventional

way.

BRS

18

Takes

in

A a code word

in

X

an

integer

This

provides

an

alternative

way

of

referencing

and

opening

for

input

scratch

files

whose names

are

decimal

integers.

The

number

in

X

is

transformed

into

its

equivalent

string

of

three

decimal

digits

enclosed

between

slashes,

5

characters

in

all,

(a

number which

exceeds

999

is

taken

to

de$ignate

the

string

/999/).

This

string

should

be a

predefined

name

in

the

caller's

file

directory.

The

subsequent

action

of

this

BRS

is

to

open

the

file

for

input

in

exactly

the

manner

of

BRS

15,

i.e.,

dependent on

bits

1 and 2

of

A;

the

return

conditions

are

the

same

as

for

BRS

15.

BRS

19

Takes

in

A a code word

in

X

an

integer

12-13

By

means

of

this

BRS

a

scratch

file

with

a

decimal-integer

name

can

be opened

for

output.

As

for

BRS

18,

the

number

in

X

is

first

transformed

to

a

string

of

three

decimal

digits

enclosed

between

slashes.

The

name

is

then

treated

as

a

possibly

new

name

for

a

scratch

file,

belonging

to

the

caller,

in

exactly

the

manner

of

BBS

16 .

Hits

0

to

5

of

A

also

have

the

same

Significance

as

for

BRS

16.

BRS

&5

Takes

in

X an

integer

The

integer

is

converted

into

a

string

of

three

decimal

digits,

as

in

BRS

18, 19. The

action

thereafter

is

exactly

as

for

BRS

63,

successfUl

deletion

being

indicated

by

a

skip

return.

12.9

Format

of

the

File

Directory,

Some

Implementation

Details

File

names,

group

names and pseudonyms

are

contained

in

8.

hash

structure

of

the

type

described

in

the

Section

14

of

this

manual.

The

first

two words

of

each

hash

table

entry

are

the

conventional

string

pointers

to

the

file

name. The

third

word

(the

string

"value")

is

a

pointer

to

a 4-word

"description

block."

In

these

four

words

is

held

all

the

information

necessary

to

characterize

the

name,

whether

it

be

the

name

of

a drmn

file,

tape

file,

special

group,

pseudonym,

etc.

Notice

that

several

entries

in

the

hash

table

may

point

to

a

Single

description

block;

the

associated

names

are

then

synonyms

for

the

same

object,

which

can

be

referenced

by

anyone

of

them.

The

conunand

DEFINE

NAME

creates

a

new

name

to

point

to

an

existing

description

block;

conversely

DELETE

NAME

detaches

the

name

from

its

description

block,

the

description

block

itself

is

lost

only

if

this

was

the

only

name

pointing

to

it.

The

format

of

a

single

hash

table

entry

with

attached

file

description

block

is

sketched

on page 12

A.

12-14

Executive

commands

and

BRSs

are

available

for

interrogating

and changing

parts

of

the

user's

file

directory.

The

commands

FILE

DIRECTORY

and

SET

MODES

FOR

FILE

are

described

in

the

manual

for

the

TSS

Executive

(Document R-22).

The

corresponding

BRSs

are

BRS

60

and

48.

12.10

Miscellaneous

Services

BRS

92 -Copy

file

to

file

By

means

of

this

BRS

infor.mation can be

copied

from one

file

to

another.

The

entry

parameters

consist

of

an

input

file

number,

an

output

file

number and

some

bits

to

determine

the

nature

of

the

files.

If

the

information

transfer

is

successfUl,there

is

a

skip-return;

if

unsuccessful,

a

no-skip

return,

possibly

preceded

by

a message.

On

entry,

the

contents

of

A

are

taken

to

refer

to

the

input

fi

Ie

as

fo

llows

:

give

the

input

file

number

give

the

file

type

bits

15

to

23

bits

3

to

5

bit

1

is

0

for

a

sequential

device

(tape,

teletype)

or

1

for

a random

device

(drum,

disk)

bit

0

is

0

for

a.

sequential

file,

1

for

a random

file

The

contents

of

B

refer

to

the

output

files.

Only

bits

0,

1,

and

15

to

23

are

significant

and have a

similar

interpretation

to

the

corresponding

bits

of

A.

The

necessary

information

for

setting

bits

0 and 1

correctly

is

returned

by BRS's 15,

16

as

bits

'/J,

1

of

X.

The

copy

will

be

successfully

terminated

when

any

of

the

following

terminators

is

read

from

the

input

file.

1)

Input

file

sequential

a)

An

EOT

(144

8)

character,

if

and

only

if

the

input

file

is

a

teletype.

b)

An

EOF

(1378)

character

for

other

type 3

files.

c)

2

consecutive

termwords (276575378)

for

all

other

sequential

files.

12-15

2)

Input

file

random

a)

1 termword

if

the

file

is

stored

on

a

sequential

device.

b)

Otherwise

the

copy

terminates

when

the

end

of

the

index-block

chain

is

reached.

The

return

after

a

successful

copy

is

with

a

skip.

Errors

Errors

may

be

a)

Calling

BRS

92

with

inadmissible

parameters.

b)

Unusual

conditions

detected

during

a

data

transfer.

Errors

of

type

(a)

may

be

anyone

of

the

following:

Attempt

to

copy a

sequential

file

to

a random

file.

Attempt

to

copy

a "random"

file

on

tape

to

a

sequential

file.

Attempt

to

copy a

non-symbolic

file

to

teletype.

Attempt

to

copy

directly

from

magnetic

tape

to

a

teletype

or

vice-versa.

They

are

all

followed

by

a

no-skip

return.

Errors

of

type

(b)

are

all

signalled

by

a

message,

which

is

sent

to

the

command

output

medium. The messages

may

be

any

of:

-END

OF

TAPE

UNTIMELY

EOF

IN

INPUT

UNT:wELY

EOR

IN

INPUT

RANDOM

FILE

TOO

BIG,

TRANSFER

TERMINATED

AT

ADDRESS

<n>

FAILED

TO

READ

INDEX

BLOCK

INPUT

ERROR

OUTPUT

ERROR

All

but

the

last

two

are

followed

by

a

no-skip

return.

In

the

case

of

the

last

two

the

transfer

continues

from

the

point

at

which

the

transfer

error

was

detected

until

the

entire

file

is

copied.

BRS

93

-

Make

a

"save"

file

Takes

in

A

the

address

of

a

core-bounds

list

in

B

the

address

of

a 2-word

map

in

X a

sequential

output

file

number

12-16

This

BRS

may

be

used

to

preserve

the

contents

of

specified

ranges

of

core

(in

the

map

given

by

B)

to

the

output

file

given

by

X;

note

that

this

file

must be

sequential.

The

core

bounds

list

addressed

by

A,

is

a

contiguous

li.t

of

positive

numbers

terminated

by

any

negative

number.

The

first

entry

of

the

list

is

ta.ken

as

a

"starting

address"

-and

is

the

address

to

which a

transfer

of

control

will

be

made

when

the

da.ta

preserved

by

this

BRS

is

read

back

into

core

by

the

GO

TO

command.

Subsequent

entries

in

the

list

are

taken

in

pairs--each

pair

defining

a

range

of

memory

from which

information

is

to

be

saved.

The

two

addresses

in

each

pair

may

be

given

in

either

order.

All

addresses

are

taken

with

the

map

whose

core

address

is

given

in

B--if

B

is

zero,

it

will

be assumed

that

the

user's

current

program

memory

is

to

be

saved.

If

the

information

is

successfully

transferred

to

the

file,

there

is

a

skip

return.

Any

failure

in

the

data

transfer

results

in

an

~ediate

no-skip

return.

The

formats

of

the

core

bounds

list

and

the

resultant

save

file

are:

Format

of

Core Bounds

List

. Format

of

save

File

i

Starting

Address 11 = min

(m

1

,n

l)

m

l u

=max

1

(~,nl)

nl

Starting

Address

·

m

2 ·

data

from

n2

core

range 11

to

ul

.

. 12

~

u2

~

data

from

core

12

to

u2

·

negative

number ·

·

·

data

from

core

~

to

'1t

term

word

term

word

12-17

BRS

94

-

Restore

a save

file

to

core

Entry

A,B =

relabeling

X =

file

no.

of

sequential

save

(type

1)

file

The

save

file,

which

should

have

the

format

described

in

BRS

93,

is

transferred

to

the

memory

given

by

the

map

in

A,B.

If

the

transfer

is

successful,

there

is

a

skip

return

with

the

starting

address

(see

BRS

93)

in

A and

the

file

number

in

X.

An

unsuccessful

data

transfer

results

in

a nO-Skip

return.

BRS

131/132 -(open

tape

for

input/output)

[privileged]

Given

in:

A =

the

desired

tape

position

(0<A<256)

B =

the

user

number

of

the

file

o~mer

(BRS

132

only)

X =

the

tape

system number

or

the

tape

unit

number

with

bit

0

set.

Return

No

Skip:

A =

error

flag

(-2<A<18)

All

errors

result

in

a

typed

message

Skip:

A =

file

number

B =

user

number

of

file

owner

X =

tape

unit

number

The

tape

can be open

for

input

(BRS

131)

without

executivity

being

set.

In

fact,

BRS

131

can

be

executed

by

users

with

operator

privileges

even

if

they

do

not

have

executive

privileges.

If

the

desired

tape

is

not

logically

mounted,

it

can

still

be

accessed

by

loading

the

unit

number

in

X and

setting

XO.

This

will

cause

the

tape

status

vector

to

record

the

tape

system

and

reel

numbers.

No

new

files

can

be

created

with

BRS

132.

A more complete

description

can

be found

in

M-l7.

13-1

13.0

Miscellaneous

Executi-..rc

Features

The

executive

provides

a number

of

BRS's which

are

services

for

the

user.

Many

of

these

are

incorporated

in

the

string

processing

system

or

in

the

floating

point

package and

are

described

in

the

next

t"TO

sections.

To

input

an

integer

to

any

radix

the

instructions

LDB =

radix

LDX

==

file

BRS

38

may

be

executed.

The

number, which

may

be

preceded

by

a

plus

or

minus

sign,

is

returned

in

the

A

register

and

the

non-numeric

character

which

terminated

the

number

in

the

B

register.

The

number

is

computed

by

multiplying

the

number

obtained

at

each

stage

by

the

radix

and

adding

the

new

digit.

It

is

therefore

unlikely

that

the

right

thing

will

happen

if

the

number

of

digits

is

too

large.

If

no

digits

are

typed,

the

Sign

bit

of

B

is

set.

To

output

a number

to

arbitrary

radix

the

instructions

LDB

-=

radix

LDX -

file

LDA

number

BRS

36

may

be

executed.

The

number

will

be

output

as

an

unsigned

24-bit

integer

unless

the

sign

bit

of

B

is

set,

in

which

case

it

will

be

signed.

If

the

magnitude

of

the

radix

is

less

than

2,

an

error

will

be

indicated.

To

get

the

date

and time

into

a

string,

the

operations

LDP

PTR

BRS

91

may

be

executed.

The

current

date

and

time

are

appended

to

the

string

provided

in

AB

and

the

resulting

string

is

returned.

The

characters

appended have

the

form:

rnm/dd/YY

hhmm:ss

Hours

are

counted

from 0

to

23.

BRS

39

returns

the

date

and

time

in

AB

as

six

8-bit

bytes

giving

year,

month, day,

hour,

minute,

second,

respectively.

BRS

123 Read

teletype

and

user

number

Entry

X =

-lor

teletype

number

Exit

A =

user

number or

O.

B =

job

number

or

O.

X

~

teletype

number

BRS

97

Find

user's

teletype

Entry

A =

-lor

teletype

number

X

==

user

number

Exit

No

skip:

user

not

entered;

A,B,X

undefined

Skip:

A

teletype

number

X

user

number

This

BRS

may

be

used

to

find

on

which

teletypes

a

user

is

entered.

A

search

is

made

to

see

if

the

user

whose

user

number

is

given

in

X

is

entered

on any

teletype

with

a number

higher

than

that

given

in

A.

If

no

such

teletype

is

found,

the

BRS

does

not

skip

on

return.

Otherwise,

there

is

a

skip

return

with

the

next

higher

such

teletype

number

in

A.

BRS

10!}

Find

user

number from

user

name

Entry

B

X

string

pointer

address

dual

file

number

Exit

No

skip:

A,B,X

undefined,

illegal

user

name

S](ip:

A:-.:

X =

user

number

BRS

104

uses

B and X

to

collect

a

user

name

in

the

same

manner

as

BRS

15.

If

an

illegal

name

is

typed,

there

is

a no-

skip

return

from

the

BRS.

The

characters

typed

are

appended

to

the

string

(if

any)

given

on

entry.

Otherwise,

there

is

a

skip

return

with

the

required

user

number

in

both

A

and

X.

13-2

BRS

195

Find

user

name

from

user

number

Entry

A,B

~

string

pointer

X =

user

number

This

BRS

reverses

th~

action

of

BRS

104.

If

the

user

number

is

valid,

it

appends

to

the

string

addressed

by

A,B

the

users

name

corresponding

to

the

given

number and

returns

with

a

skip.

If

the

user

number

is

not

valid

the

BRS

does

not

skip

and

A,B,X

are

unchanged.

BRS

100 Read subsystem

relabeling

13-3

Requires

in

B

the

address

of

a

string

pointer

to

the

subsystem

name

in

X a

dual

file

number

or

-1.

Returns

skipping

with

the

subsystem

relabeling

in

A,B and

the

starting

address

in

X.

14-1

14.0

String

Processing

System

The

string

processing

system

(Sps)

consists

of

eight

SYSPOPs

and

six

BRSs.

SPS

strings

are

stored

three

8-bit

characters

per

word.

Strings

are

addressed

by

two-word

pointers.

The

first

word

contains

the

character

address

of

the

character

before

the

first

character

of

the

string.

The

second word

contains

the

character

address

of

the

last

character

of

the

string.

The

character

address

of

a

character

is

obtained

by

multiplying

by

3

the

address

of

the

word

containing

it

and

adding

0,

1

or

2

depending on

its

position

in

the

word.

All

string

pointers

contain

character

addresses.

The

character

pointers

used

by

GCI,

GCD,

WCI

and

WCH

must have

the

first

8

bits

cleared.

The

following

SYSPOPs

are

independent

of

the

hash

table

mechanism which

is

described

later.

Any

of

them

may

be

indexed

or

indirectly

addressed

(as

may

most

other

SYSPOPs).

14.1

String

Pointer

Load and

Store

Qperations

LDP

ADDR

loads

the

A and B

registers

with

the

contents

of

ADDR

and

ADDR+l.

X

is

undist~bed.

STP

ADDR

stores

the

contents

of

the

A and B

registers

in

locations

ADDR

and

ADDR+l.

A,

B,

and X

are

undisturbed.

14.2

String

Read and

Write

Operations

GCI

ADDR

tries

to

load

the

A

register

with

the

first

character

of

the

string

addressed

by

the

pointer

pair

in

ADDR

and

ADDR+l.

If

the

string

is

null

or

empty

(i.e.,

if

the

contents

of

ADDR

is

greater

than

or

equal

to

the

contents

of

ADDR+l),

then

nothing

is

done and

the

next

instruction

in

sequence

is

executed.

If

the

string

is

not

null,

its

first

character

is

loaded

into

A

right-justified

and

the

contents

of

ADDR

are

incremented

by

1,

so

that

the

string

pointer

now

points

to

the

string

with

the

first

character

deleted.

The

top

16

bits

of

A

are

cleared,

and

the

next

instruction

in

sequence

is

skipped.

Unless a copy

of

the

original

pointer

is

saved,

the

contents

of

the

string

are

effectively

destroyed

by

GCT.

For

example,

the

code:

GCl

STRrnG

BRU

¢UT

BRM

PR¢CESS

BRU

* - 3

~ur

14-2

will

call

the

subroutine

PR¢CESS

with

each

character

of

the

string

addressed

by

STRING and

go

to

¢UT

after

the

last

character

is

processed.

To

save

the

contents

of

STRING,

the

following

comma~ds

could

have been

executed

first:

LDP STR:mG

STP

SAVE

etc.

The

X

register

is

not

disturbed

by

Gel.

The

B

register

is

destroyed.

Timing:

43

cycles.

GCD

is

in

every

way

similar

to

GCl

except

that

the

character

is

taken

from

the

end

of

the

specified

string

and

the

second

string

pointer

is

decremented.

WeI

ADDR

~~ites

the

character

in

the

last

8

bits

of

A on

the

end

of

the

string

addressed

by

ADDR.

The

contents

of

ADDR+l

are

incremented

by

1.

A and X

are

not

changed. B

is

destroyed.

To

use

a

WeI

in

constructing

a

string,

it

is

necessary

to

start

with

a

null

string.

Suppose

the

string

is

to

be

put

into

a

buffer

called

LINE

and

defined

by

LINE

BSS

20

The

instructions

LDA

=LINE

MUL

=3

LSH

23

STA

PI'R

STA

PTR+l

will

make

PTR

a

pointer

to

a

null

string

beginning

(and

ending)

with

the

first

character

(not

the

oth)

in

LINE.

To

start

with

the

oth

character

a

SUB=l

could

be

inserted

after

the

LSH.

LINE

can

now

be

filled,

say

from

the

teletype

by

CIO

r::

0

WeI

Pm

BRU

* - 2

weD

is

the

same

except

that

it

writes

the

character

on

the

front

of

the

string

and decrements

the

first

pointer.

WCH

takes

a

character

in

A and a

table

address

in

the

operand

field.

The

ta.ble

comprises

three

words:

ZRO

CLB

ZRO

CUB

OP

ADDR

14-3

WCH

tries

to

write

a

character

into

the

area

defined

by

the

character

addresses

CLB,

CUB.

Provided

that

CUB>CLB,

WCH

will

write

the

character

in

A

into

character

position

CLB+l

and

increment

CLB.

If

CLB>CUB

the

character

is

not

written

and

control

is

transferred

to

the

third

word

of

the

table

with

A and

X

undisturbed

and

the

address

of

the

offending

WCH

in

B. This

can be

an

error

trap

or

an

exit

to

a

routine

which

allocates

more memory,

by

garbage

collection

or

otherwise,

for

further

WCH's.

14.3

String

Compare

Operations

SKSE

ADDR

skips

if

the

string

addressed

by

the

pointer

in

AB

is

identical

with

the

string

addressed

by

AnDR.

If

the

strings

are

of

different

lengths

or

have

different

contents,

SKSE

does

not

skip.

This

instruction

is

essentially

identical

to

SKE,

except

that

it

acts

on

strings

rather

than

numbers.

A,

B,

X

are

not

disturbed

by

SKSE.

SKSG

ADDR

skips

if

the

contents

of

the

string

addressed

by

AB

is

greater

than

the

contents

of

the

string

addressed

by

ADDR

and

ADDR+l.

Comparison

is

made

character

by

character,

and

terminates

with

the

first

unequal

characters;

the

numerical,

internal

code

representation

of

characters

is

used

to

determine

inequality.

If

the

strings

are

equal

for

the

entire

length

of

the

shorter

one,

the

longer

one

is

indicated

as

the

greater.

A,

B and X

are

not

disturbed

by

SKSG.

14.4

String

Input/Output

BRS

33

accepts

a

string

pointer

address

in

A,

a

file

number

in

X and a

"terminal

character"

in

B.

It

collects

characters

from

the

file

and appends them

to

the

string

until

the

terminal

character

is

seen;

this

is

not

added

to

the

string.

It

then

returns

the

updated

st.ring

pointer

in

AB;

the

string

14-4

pointer

in

core

is

also

updated.

If

bit

0

of

A

is

set

on

entry

the

string

is

taken

as

null

with

the

second

pointer

equal

to

the

first.

BRS

34

accepts

a

file

number

in

X,

a word

address

in

A and

a

count

in

B.

It

outputs

B

consecutive

characters

starting

with

the

first

character

of

the

specified

word.

If

B=-l

on

entry

characters

are

output

until

I

is

encountered

and

the

character

$

is

interpreted

as

carriage

return,

line

feed.

ERS

35

accepts

a

fi~e

number

in

X and a

string

pointer

in

AB.

It

outputs

the

string

to

the

fi1e.

14.5 Hash Table Lookup

Instructions

The

hash

table

is

a

structure

for

minimizing

the

effort

required

to

perform

certain

scan-and-compare

operations

when

the

operands

are

strings.

A

hash

table

is

a

contiguous

set

of

3-word "augmented

string

pointers."

The

addresses

of

the

first

and

last-pIus-one

locations

of

the

hash

table

we

shall

denote

by

HT,

EHT

respectively.

Each

augmented

string

pointer

occupies

three

consecutive

locations

of

the

hash

table.

Bits

8

to"23

of

each

of

the

first

two

locations

hold

the

actual

string

pointer;

bits

0

to

7

of

these

two

words,

as

well

as

the

entire

third

word

(the

so-called

string

"value")

may

hold

arbitrary

information.

Note, however,

that

bits

0

to

7

of

the

string

pointer

words

~

be

zero

if

used

with

GCI

or

WeI.

There

are

three

BRSs

to

perform

operations

on a

hash

table:

they

are

BRS

5,

BRS

6,

BRS

37.

BRS

6

is

used

to

introduce

new

strings

into

the

table.

BRS

5 and

BRS

37

each

perform

a

scan

of

the

hash

table

for

a

string

to

match a

given

string.

Before

using

BRS

5

and

BRS

6

to

insert

string

pointers

into

an

initially

empty

hash

table,

the

hash

table

area

must

be

cleared

to

zeros.

BRS

;

takes

a

string

pointer

in

A,

B,

a

table

address

in

X.

The

table

comprises 3 words:

ZRO

HT

ZRO

EHT

ZRO

0

14-5

The

first

two

define

the

hash

table

bounds,

the

third

is

used

for

communication

with

BRS

6.

BRS

5

searches

the

hash

table

for

a

string

to

match

the

given

one.

If

successful

it

returns

in

B

the

address

of

the

hash

table

string

pointer

(the

string

"indextl)--and

in

A

the

string

"value";

it

skips

on

return.

If

the

search

is

unsuccessf'ul,

BRS

5

returns

with

A,

B unchanged and

the

addre s s

of

the

next

free

table

entry

in

word 3

of

the

table

(this

will

be

-1

if

the

table

is

full).

X

is

not

disturbed.

BRS

6

takes

a

string

pointer

in

A,

B and a

table

address

in

X.

The

table

is

as

for

BRS

5.

This

operation

inserts

the

string

pointer

into

the

hash

table

at

the

point

determined

by

the

last

BRS

5 which

failed

(i.e.,

at

the

location

specified

by

the

third

word

of

the

table).

If

this

word

is

-1,

there

is

an

illegal

instruction

trap.

BRS

6

is

intended

for

use

only

in

inserting

into

the

hash

table

a

string

pointer

for

which

BRS

5

failed

to

find

a match and

should

not

be

used

except

after

a

failing

BRS

5.

Furthermore,

string

pointers

should

not

be

placed

in

the

hash

table

except

with

BRS

6

(otherwise

the

scanning

algorithm

used

in

ERS

5

will

not

work). Note

that

BRS

6 does

not

physically

move

the

characters

to

which

(AB)

points.

On

exit,

BRS

6

returns

in

B

the

address

of

the

first

word

of

the

new

hash

table

entry

and

in

A,

the

"value"

word

of

the

entry;

X

is

not

disturbed.

To

delete

a

hash

table

entry,

put

-1

(not

0)

in

the

first

word.

BRS

37

takes

a

dual

file

number

in

A,

a

string

pointer

address

in

B and,

in

X,

the

address

of

two words

conta.ining

table

bounds

HT,

EHT.

A

dual

file

number

is

a

single

word

holding

an

output

file

number

in

the

first

12

bits

and an

input

file

number

in

the

second.

If

the

output

file

number

is

zero,

the

user's

teletype

will

be

used.

The

table

has

the

same

form

as

a

hash

table,

but

the

string

pointers

may

be

put

into

it

in

arbitrary

order;

it

is

~

necessary

to

use

ERS

5 and

BRS

6.

The

behavior

of

BRS

37 depends on

the

command

recognition

mode

currently

set

in

the

exec

(see

R-22,

Section

5.5).

If

the

14-6

mode

is

BEGINNER,

the

hash

table

is

scanned

for

a

string

to

match

exactly

the

given

one.

If

none

is

round

but

the

given

string

matches

the

initial

part

of

some

hash

table

string,

characters

from

the

input

file

are

appe~ded

to

it

until

either

an

exact

match

is

obtained

or

a match becomes

impossible.

The

exit

is

described

below.

If

the

mode

is

NOVICE,

the

hash

table

is

scanned

for

a

string

to

match

the

given

one.

If

none

is

found

but

the

given

string

matches

the

initial

part

of

some

hash

table

string,

characters

from

the

input

file

are

appended

until

the

string

is

long

enough

either

to

determine

a

unique

hash

table

string,

with

a

matching

initial

part,

or

for

no

match

to

be

possible.

In

the

former

case,

if

the

hash

tabl~

string

now

contains

three

or

less

as-yet-unmatched

characters,

more

characters

are

taken

from

input

until

an

exact

match

is

obtained

or

no

match

is

possible;

if

the

hash

table

string

contains

four

or

more

as-yet-unmatched

characters

these

unmatched

characters

are

sent

to

the

output

file.

If

the

input

file

is

the

teletype,

BRS

37

waits

until

all

the

characters

have

been

output,

and

the

input

file

buf"fer

is

cleared

before

exit.

If

the

.mode

is

EXPERT

the

hash

table

is

scanned

for

a

string

to

match

the

given

one.

If

none

is

found

but

the

given

string

matches

the

initial

part

of

some

hash

table

string,

characters

from

the

input

file

are

appended

until

the

string

is

long

enough

either

to

determine

a

unique

hash

table

string,

with

a

matching

initial

part,

££

for

no match

to

be

possible.

In

the

former

case

the

rema.ining

characters

of

the

hash

table

string

are

sent

to

the

output

file.

Exits

are

as

follows:

The

no-match

condition

causes

a

no-skip

exit

with

a

string

pointer

in

AB

to

the

string

so

far

collected;

X

is

undisturbed.

If

a match

is

found

there

is

a

skip

exit

with

the

address

of

the

matching

table

entry

in

A and

the

string

value

in

B,

X

is

undisturbed.

The

following

subroutine

illustrates

a

use

of

the

hash

table

facility.

A

string

is

input

from

the

teletype

and appended

to

WCH

string

storage

until

a

carriage

return

is

encountered;

14-7

it

is

assumed

that

string

storage

does

not

overflow

in

the

process.

The

hash

table

is

then

searched

for

the

string;

if

it

is

not

already

there

it

is

inserted.

In

any

case,

an

exit

is

made

with

the

value

of

the

string

in

A

and

the

address

of

the

string

pointer

in

B.

On

entry

X

contains

the

address

of

the

table

for

BRS

5, 6.

CTL

is

the

address

of

a

table

for

WCH.

INPUT

LOOP

WRITE

ZRO

LDA

STA

TCl

SKE

BRU

LDA

LDB

BRS

BRS

SBRR

WCH

BRU

INPL

CTL

remember

beginning

of

string

TEMP

CHAR

=l55B

terminator?

WRITE

TEMP

yes

CTL

5

6

INPUT

CTL

LOOP

15-1

15.0

Floating

Point

Instructions

This

section

describes

the

floating

point

operations

which

are

available

in

the

system.

SYSPOPs

are

provided

to

do

floating

addition,

subtraction,

multiplication

and

division

and

to

convert

under

format

control

between

the

internal

floating

point

repre-

sentation

and an

external

representation

as

a

string

of

digits,

decimal

points

and E

(for

exponent).

BRS's

exist

which

perform

input-output

and

conversion

automatically

without

involving

the

user

with

the

external

string

representation.

All

these

operations

preserve

the

X

register,

except

input

routines

which

return

the

terminal

character

in

X.

Most

destroy

AB

by

leaving

a

result

there.

15.1

Floating

Point

Representation

A

floating

point

number

is

held

internally

as

two

24-bit

machine

words.

The

format

is

MANTISSA

3813_:140

471

_ _

EXPONENT

o 1

The number

is

always

normalized:

i.e.,

the

most

significant

bit

of

the

mantissa

differs

from

the

sign

bit.

All

floating

point

operations

expect

normalized

operands

and produce

normalized

results.

Both

mantissa

and exponent

are

treated

as

two_complement

numbers.

The

two words

of

the

floating

point

number

appear

in

the

AB

register

or

in

memory

in

the

order

indicated.

A

floating

point

number

is

represented

externa~

as

a

string

of

characters.

This

string

has

the

following

form:

[!]

[string

of

digits]

[.[string

of

digits]]

[E[~]string

of

digits)

The

brackets

.indicate

optional

constituents.

At

least

one

digit

must

appear.

Imbedded

blanks

are

not

allowed.

The

E

indicates

that

the

preceding

number

is

to

be

multiplied

by

the

power

of

10

specified

after

the

E.

In

general

a

floating

point

number

being

input

may

take

any form which matches

the

template

above.

On

output

the

form produced

will

be

determined

by

the

format

specified.

15-2

15.2

Floating

Fbint

Arithmetic

There

are

four

SYSPOPs

to

perform

floating

point

arithmetic.

Each

of

these takes

one

operand

from

AB

and

the

other

from M and

M+l

where M

is

the

effective

address

of

the

instruction.

The

result

is

left

in

AB

in

normalized

form.

If

its

magnitude

is

greater

than

5.7896044E+76,

the

overflow

indicator

will

be

turned

on and

this

value

will

be

returned.

The

overflow

indicator

is

not

cleared

by

any

of

these

instructions.

In

this

respect

the

floating

point

POPs

behave

exactly

like

the

integer

machine

instructions:

a sequence

of

operations

can

be performed

before

the

overflow

bit

is

tested.

The

bit

will

be on

if

any

operation

caused

an

overflow.

If

the

r.esult

is

less

than

O.8036l6E-77,

it

will

be

set

to

O.

No

indication

will

be

given.

The

four

operations

are:

FAD

Floating

add

FSB

Floating

subtract

FMP

Floating

multiply

FDV

Floating

divide

An

attempt

to

divide

by

0

will

produce

an

overflow.

Two

SYSPOPs

are

provided

for

loading

and

storing

double

words.

The

words

involved

need

not

be

floating

point

numbers,

of

course.

wad

pbinter:

LDP

M

puts

the

contents

of

M and

M+

1

into

AB.

Store

pointer:

STP

M

puts

the

contents

of

AB

into

M and

M+l.

Three BRS's

provide

for

unary

operations

involving

floating

point

numbers.

Floating

negate:

BRS

21

returns

in

AB

the

negative

of

the

floating

point

number

supplied

in

AB.

Fix:

BRS

50

converts

into

a double

precision

fixed

point

number.

The

integer

part

appears

in

A.

The

fraction

part

appears,

left

justified,

in

B.

If

the

integer

is

too

large,

the

most

significant

bits

will

be

lost.

The

integer

part

is

the

next

smaller

integer.

I.e.,

IP(-1.2)=-2.

Float.

BRS

51

converts

the

integer

in

A

to

a

normalized

floating

point

number

in

AB.

15-3

15.3

Input/Output

Formats

and

Conventions

Every

1/0

operation

allows

the

user

to

specify

a

format

in

the

X

register.

Format

specifications

are

based

on

Fortran

conventions,

and

are

specified

as

follows:

Bit

of

X

Field

Name

0-2

T

3-8 D

9-14 w

15

0

16-23 N

Examples:

F6.3

E17·9

15

Significance

Format

types:

1

integer.

2 E

format

with

the

number

right

justified

within

the

specified

field.

3 F

format

with

the

number

right

justified

within

the

specified

field.

4 E

format

with

the

number

left

justified

within

the

specified

field.

5 F

format

with

the

number

left

justified

within

the

specified

field.

Number

of

digits

following

the

decimal

point.

Total

field

width

If

the

field

width

is

0,

the

1/0

will

be done

in

free

format.

Overflow

action.

1/0

file

number. 0

always

refers

to

the

teletype.

ISC

and

SIC

ignore

this

field.

30306000

21121000

1000)000

On

input

only

the

Wand

N

fields

are

significant.

Note

that

exactly

W

characters

w111

be

read

on

input

(unless

W=O).

Leading

blanks

and

any

trailing

characters

are

ignored.

Free

format

input

will

accept

as

many

characters

as

it

can

in

constructing

a

number which

fits

the

external

representation

described

above.

The

input

operations

always

return

a

floating

point

result.

They

skip

unless

overflow

occurs,

in

which

case

they

return

the

largest

possible

nwnber and do

not

skip.

Any number

of

digits

may

be

provided:

the

first

11

digits

after

any

leading

zeros

will

be

the

ones

used.

On

output

the

W

field

should

be

made

large

enough

to

accommodate

Sign,

dec~al

point,

E,

sign

of

exponent

and

exponent

(if

the

format

type

requires

any

of

these

elements)

as

well

as

the

digits

of

the

number

it.self.

Sec

the

discussion

01

error

conditions

belOi'T.

Tht:

sign

is

printed

only

if

the

number

is

negative.

There

are

two

ways

to

output

an

integer:

(1)

integer

format,

or

(2)

F

format

with

0

in

the

D

field.

The

former

requires

that

the

number

in

the

A

register

be

in

integer

form;

the

latter

expects

a

floating

point

number

in

AB.

Free

format

output

generates

between 11 and

16

chara.cters.

If

the

magnitude

of

the

number

is

between

lEO

and lE9,

ten

digits

are

output

with

the

decimal

point

properly

placed.

Otherwise,

exponential

format

is

used;

in

particular,

the

format

E15.9.

For

example,

the

following

numbers

might

be

generated

by

the

free

format

output.

5.379605400 -145362.59h7 5.789604462E+76

15.4

Input/Output

Operations

Two

SYSPOPs

are

available

to

convert

between

the

internal

binary

representation

of

a

floating

point

n1h~ber

and

its

external

decimal

representation

as

s.

string

of

characters.

The

string

is

stored

nnd

addressed

according

to

the

standard

system

conventions.

String

to

internal

conversion

(SIC):

Characters

are

read

from

the

string

pointer

addressed

by

the

pop

under

control

of

the

format

in

X.

The

internal

representation

of

the

number

is

returned

in

AB.

The

first

character

after

the

number

is

returned

in

X

if

free

format

was

specified.

Internal

to

string

conversion

(ISC):

The

number

in

AB

is

converted

according

to

the

format

in

X and

the

resulting

external

represen-

tation

is

written

onto

the

end

of

the

string

addressed

by

the

POP.

The

string

pointer

is

updated.

Two

BRS's

are

available

to

do

input/output

and

conversion

at

the

same

time:

Floating

input:

BRS

52.

Input

takes

ple.ce

according

to

the

format

word

in

X.

The

operation

of

this

BRS

is

identical

to

that

of

SIC.

15-5

Floating

output:

"BRS

53. Output

takes

place

according

to

the

format

word

in

X.

The

operation

of

this

BRS

is

identical

to

that

of

ISC.

15.5 Output

Error

Conditions

There

are

four

possible

error

conditions.

~Vhen

one

of

these

conditions

occurs

the

following

action

is

taken:

Code

1

2

3

4

a)

Interrupt

5

is

generated

b)

An

error

code

is

put

into

location

200B

c)

The

indicated

corrective

action

is

taken

and

execution

continues.

Condition

T

field

is

not

1,2,3,4

or

5

Exponent

field

is

too

small

Integer

exceeds

8388607

in

magnitude

Field

for

F-conversion

too

small

Action

Assume

2(E

format)

Discard

characters

from

the

left

or

take

overflow

action.

Use

8388607

Discard

characters

from

the

left

or

take

overflow

action.

If

either

of

error

types

2

or

4

occurs

and

bit

0

in

the

format

word

is

set,

then

the

output

field

will

be

filled

with

*'s.

A-I

BRS

TABLE

NAME

NUMBER

FUNCTION

---

MONOPN

I

Open

file

9-4, 9-8

MONCLS

2 Close

file

9-4

---7

{<.svD5Jf 3 (

IJ

c.-

Iy-.

O~fA"1

t.r

IJ

'}~e

~S

MPl' 4

Release

memory

5-3

SSCH

5

SPS

search

14-5

SSIN

6

SPS

insert

14-5

DCLR

7

Release

all

space

acquired

10-3

via

BRS

126

IOH

8 Close

all

files

9-4

FKST

9

Open

fork

3-1

PPAN

10

Progrwmmed

panic

3-6

CIB

11

Clear

input

buffer

7-5

CET

12

Declare

echo

table

7-2

SKI

13

Skip

if

input

buffer

empty 7-5

OOB

14

Wait

for

output

buffer

empty 7-5

EXGIFN

15

Symbolic

input

file

name

12-6

EXGOFN

16

Symbolic

output

file

name

12-8

UABORT

17

Close

all

file

s 9-2

EXSIFN

18

Scratch

input

file

12-12

EXSOFN

19

Scratch

o~tput

file

12-12

CFILE

20

Close

file

9-2

FNA

21

Floating

negate

15-2

LNKS

23

Link

TTY

7-6

LNKC

24

Unlink 7-7

MSGS

25

Set

AM

and AI

bits

7-4

SKROUT

26

Skip

if

rubout

waiting

(exec)

3-6

ASTT

'Z7

Attach

TTY

7-3

RSTT

28

Release

TTY

7-3

C~B

29

Clear

output

buffer

7-5

A-2

NAME

NUMBER

FUNCTION

FKRD

30

Read

fork

3-3

FKWT

31

Wait

for

fork

3-3

FK'lM

32

Terminate

fork

3-3

GETSTR

33

Collect

string

14-3

~t11'MSG

34

Output message 14-4

¢urSTR

35

Output

string

14-4

¢UTNUM

36

. Output number 13-1

GSI.¢¢K

37

General

string

lookup

14-5

GETNUM

38

Read number 13-1

RMDY

39

Read

date

and time 6-1

RDET

40

Read echo

table

7-2

I¢RET

41

Return from I/O subroutine·

11-2

RREAL

42

Read

clock

6-1

RDRL

43

Read

relabeling

5-2

STRL

44

Set

relabeling

5-2

SQ~

45

Dismiss on quantum

overflow

2-3

NR~UT

46

Turn

rubout

off

(exec) 3-6

SR~UT

47

Turn

rubout

on (exec) 3-6

SETFDC

48

Set

fd

control

word 12-11

SRIR

49

Read

interrupts

armed 4-2

FFIX

50

Fix

15-2

FFLT

51

Float

15-2

FFI

52

Formatted

floating

input

15-4

FF¢

53

Formatted

floating

output

15-5

((I(

S B (

~P)54

MRSB

55

Make

or

release

resider.t

block

MBEX

56

Make

block

executive

5-4

C~

57

Guarantee

16ms

computing 2-3

SSMF

58

Define secondary

memory

10-2

f'..pA 1

59

Read

mT

RFDC

60

Read

file

directory

entry

12-11

SGDEF

61

Define

special

group 12-4

SGDEL

62

Delete

special

group

12-5

NAME

NUMBER

EXDEL

63

64

EXSFDL

65

DFDL

66

67

EBSM

68

GBSM

69

/::;c

S

""

A

70

SKXEC

71

EXDMS

72

*EPPAN

73

~

t:-s

Lvi

74

S/J:J

I~

-

f"S

fr-~

75

f-'5

""

-,

76

f:.sl~

77

SAIR

78

SIm

79

MBRO

80

WHEAL

81

82

'f.0~/AAr

83

.,

84

SET8p

85

CLR8p 86

A-3

FUNCTION

Delete

named

file

12-10

Delete

scratch

file

12-13

Delete

drum

file

(contents

only)

9-4

~

V'l/d

;C~

of

~

q -tj'

Enter

block

in

SMT

(exec

only)

5-3

Get

SMT

block

to

PMT

5-3

(exec

only)

Skip

if

executive

6-1

Exec

dismissal

(exec

only)

2-5

Economy

panic

3-4

'Ai]

OP

'/...J~JP()~)

""

r:r

P

't

1)

':

fl/)-

f

Arm

interrupts

Cause

interrupt

Make

block

RO

Dismiss

for

specified

time

Sys

go

Set

special

teletype

output

Clear

special

teletype

output

4-1

4-1

5-3

6-1

RTEX

FS

uf

DFR

88

Read

execution

time

7-7

7-7

6-1

EXRTIM

ECCOPY

ECSAVE

ECPIAC

ECDUMP

ECRECV

89

;4?) -;r

f~

90

Declare

fork

for

rubout

91

92

93

94

95

96

Time

to

string

Copy

Save

Place

Dump

Recover

3-5

13-1

12-14

12-15

12-17

NAME

I J

KB1¢¢

EXCNUN

EXCUNN

FKWA

FKRA

FKTA

DMS

RDU

BRSRET

TSOFF

MTDI

CKDOPN

RURL

SURL

TGET

TREL

AIMTE

DmTE

MPAN

RTUN

RDRM

WDRM

DGET

DREL

)

~/

f«.~f)

NUMBER

97

98

99

100

102

103

104

105

106

107

loB

109

110

III

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

1'Zl

128

A-4

FUNCTION

Find

user

13-2

Read subsystem

relabeling

Convert

name

to

user

number

Convert

user

number

to

n~e

Wait

for

any

fork

to

terminate

Read

all

fork

statuses

Terminate

all

forks

13-3

13-2

13-2

3-3

3-3

3-3

Dismiss

5-1

Read

device

and

unit

9-5

Return

from exec

BRS

(exec

only)

6-2

Turn

off

teletype

station

7-4

(exec

only)

Disco"nnect W-buffer

(exec

only)

9-6

Skip

if

no drum

files

open

Read

user

relabeling

5-3

Set

user

relabeling

5-3

Reserve

tape

unit

(exec

only)

9-6

Release

tape

unit

(exec

only)

9-6

Assign

PMT

entry

(exec

only)

5-3

Release

specified

PMT

entry

5-3

S~ulate

memory

panic

{exec

only)6-2

Read

teletype

and

user

number

13-2

Read

2K

block

10-3

Write

2K

block

Assign

2K

page

Release

2K

page

10-3

10-3

10-3

A-5

NAME

NUMBER

FUNCTION

,RQ--

fl5

129

RDBA

130

Read drum

assignment

Pm

131

Position

tape

to

read

file

12-17

PTW

132

Position

tape

to

write

file

12-17

(exec

only)

LfV

e:

[)

133

jJ1-1

i\P

f

SKUEX

134-

Skip

if

caller

executive

fr

Pl

cJ

/

fl

135

'i

!1:,1

"R-

P

/(--TY

I .

~~I

F,

/'

I.

136

fl

Celli

137

'l

'J

WIR

138

Wait

for

input

request

7-5

NTOS

139

Suppress

or

allow

output

7-7

MFLSH

140

Force drum/core

correspondence

5-5

RSCP

141

Read

status

of

caller

6-2

SSCP

142

Set

status

of

caller

6-2

RDSS

143

Read

status

9-1

STST

144

Set

status

9-1

BIO

TCO

TCI

BRS

CTRL

SBRR

SBRM

STP

LDP

GCl

WCH

SKSE

SKSG

CIO

WIO

WCI

FAD

FSB

FMP

FDV

EXS

~ST

1ST

SAS

LAS

DW¢

DWI

DBC

DBI

ISC

SIC

116

175

114

173

172

171

170

167

166

165

164

163

162

161

160

157

156

155

154

153

152

151

150

147

146

145

144

143

142

141

140

SYSTEM

PROGRAMMED

OPERATORS

Block

input-output

Teletype

character

output

Teletype

character

input

Branch

to

system

Input-output

control

System

branch

and

return

System

subroutine

call

Store

pointer

Load

pointer

Get

character

and

increment

Write

character

Skip on

string

equal

Skip on

string

greater

Character

input-output

Word

input-output

Write

character

and

increment

Floating

add

Floating

subtract

Floating

multiply

Floating

divide

Execute

instruction

in

system

mode

Output

to

specified

teletype

Input

from

specified

teletype

Store

in

secondary

memory

Load from

secondary

memory

Drum

word

output

Drum

Word

input

Drum

block

output

Drum

block

input

Internal

to

string

conversion

(floating

output)

String

to

internal

conversion

(floating

input)

B-1

9-3

7-2

7-2

Appendix 1

9-4,

9-6

14-1

14-1

14-1

14-3

14-3

14-3

9-2

9-3

14-2

15-2

15-2

15-2

15-2

6-2

7-4

7-4

10-3

10-3

10-1

10-1

lO-2

10-2

15-4

15-4

B-2

GCD

137

Get

character

and decrement

14-2

STr

136

S~ulate

teletype

input

7-7

weD

135

\'lri

te

character

and decrement

14-2

STO

134

Steal

teletype

output

7-7

BPI'

135

Breakpoint

(BRS

10)