R 21_TSSref Man 21 TSSref

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User Manual: R-21_TSSrefMan

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REFERENCE MANUAL

TIME-SHARING SYSTEM

L. Peter Deutsch
Larry Durham
Butler W. Lampson
University of

California~

Berkeley

Document No. R-2l
Revised October 22, 1968
Office of Secretary of Defense
Advanced Research Projects Agency
20325
Washington, D. C.

()
TABLE OF CONTENTS

······

1.0 Introductory •
2.0 The Scheduler.
PAC TABLE.
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 Features
7.0 Teletype Input-Output.
•
TELETYPE SYSTEM POINTERS
TELE'rYPE ~LE
•
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.
Format 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 OVen Files.
10.0 Random Drum Files.
•
10.1 Direct Drum Access
11.0 Subroutine Files

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()

···.

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.....
·. . .· .·
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·
·
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· · · · · . · .. .. • . ..
··· ··· .
·

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···

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1-1
2-1
2A

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
SA
SA

8B
9-1
9-1
9-7
9-11
9-11
10-1
10-3
11-1

I
I

I
II
i

.... .......

12.0 File
12.1
12.2
12.3
12.4
12.5
TAPE

Naming System • • • • •
File Naming. • • • ••
Accessing Other Users' Files, Special Groups •••
Pseudonyms . . . • . • • . • • . . .
Doing I/O to Files, File Numbers
Opening Input Files. • • . • •
or PERMANENT FILES. . • •
SCRATCH FILES. .
. .. ..
BUILT-IN FILES •
SPECIAL GROUPS •
PSEUDONYMS. • .
FILE DIRECTORY DESCRIPTION • •
USER DIRECTORY DESCRIPTION •
..
12.6 Opening Output Files ••.
12.7 Miscellaneous File Operations ••
12.8 Opening Scratch Files . • • . • •
12.9 Format of the File Directory, Some Implementation

...

.....

. ...

Details . . . . . . . . . . . . .

....

. ..

....

leA-2
l2A-2

...

... .

12-13
12.. 14

13-1
14-1
14-1
14-1
14,,3
14-3
14-4
l5-1
l5-1
l5-2
15-3
l5-4
A.. l
. B-1

....

leA-l

leA-3
leA.. 4
12-8
12-10
12-12

12.10 Miscellaneous Services ••••
13.0 Miscellaneous Executive Features • • . . . . . . .
14.0 String Processing System. • • • . • • . . • • .
J.4.1 String Pointer Load and Store Operations. • • .
14.2 String Read and Write Operations .
14.3 String Compe.re Operations ••• • .
.
14.4 String Input/Output. • • . • •
14.5 Hash Table Lookup Instructions .
l5.0 Floating Point Instructions • • • • •
l5.1 Floating Point Representation ••
l5.2 Floating Point Arithmetic •••
l5.3 Input/Output Formats and Conventions.
.. ..
15.4 Input/Output Operations ••
.
.
.
BRS '1!A.BLE. ..
SYSTEM PROGRAMMED OPERATORS. •

12-1
12-2
12-4
12..5
12-5
12-6
leA-l
leA-l

....

1-1
1.0 Introductorl

()

(~/

The Berkeley Time-Sharing System is divided into three major
parts: The monitor, the executive, and the subsystems. Only
the firat 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 u.er controll the syatem trom hil 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 ~ograms.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 ~B 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 canpute before it is dismissed. A job table called QUR
countrthe 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 in the discussion are measured
in periods of the 60-cycle compu·t.er clock.

PAC TABLE

PNEXT
PL

next queue or next program in queue
U

0
~

file 11= of 8
subroutine 0
file

saved (p)

saved (A)

saved (B)

saved (X)

RLl

first pseudo-relabeling register .

RL2

second pseudo-relabeling register
11 12

PPTR
PrEST
PQU
PTAB

PF~RK

PD¢WN
3activation
condition

000
E

li·· 2

X B
0

0 11.0

test word address, or other
relevant parameter
11 12
9
PPAR
QUTAB

P.O

job number

T N E 14
T w T M

23
23

panic table address

23
!EM

UN • user mode (1) or system
OV

= overflow

PD¢WN .. PACT address of lower fork (if an,y)
PFPRK .. PACT address of' upper fork (if' any)
PPAR III PACT address of parallel fork (ends with 0)
QUXAB .. address of word in table indicating quantum lengths
EB = exec BRS
EX • executive type program
QN = saved queue number if on QOV TW = waiting for termination
!EM

1M
MT
I

= interrupt

= local

enabled mask

memory
= add. no memory

NT
EM

= non-terminable
= destroy memory when fork
is terminated

2-2

A program is allowed to run for a fixed period of t 1me I after
which it i8 dismissed if any other programs are ready to run. This
time is called a !2!li quantum. It may' be different for dirterent
progr&llli. In tact, the size of the long quantum il determined by
the entry in QTAB which 1s pointed to by the program's QU'!'AB in PACT.
When a program is activated, it is tirst allOwed to run tor a
short 9,U:antum. During this time it cannot be dismissed except by its
own request. The length of the short quantum is tentatively going
to be the lame for all users. It 18 put into a word called TIME;
the long quantum is also put into a word called !TIME at this time.
Both are decremented at every clock cycle.
When TlME 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 it MY programs dismissed
for I/O are ready to run. It may alao be dismissed when the long
quantum il exhaulted it any other programs are waiting to run. In
either case it il said to be dismissed for quantum overflow. If
AOTR indicates that another program dismissed for I/O is ready to
.run at the end of the Ihort quantum" the program is also dismissed
for quantum .overflow .
In order to allow an effiCient implementation of this scheme,
AC'm is incremented by every :l.nterruptrout:l.ne which takes action
al1ow1ng a program which is waiting for I/O to run. ACTR is set
to-l when a program is activated.
When a program is dilDlissed tor I/O, TTIME is put into QUR.
When the prograa is reactivated, TTJME i8 set trom Q,UR. TlME i. relet
to the fuU short. quantum. That is, the long quantum is allowed to
run down while a program computes, regardless of whether it has to
wait tor I/O between ccmputations. On the other hand, a program is
alN8 liven a full ahort q,uantum. If' a program is dilDlissed tor
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 4; causes the
user to be di_used as though he had overflowed his quantum.
BRS 57 guarantee. to the user upon return at least 16 msec of

2-3

C-)
/

uninterrupted computation. This feature is implemented by dismissing
the user if less than 16 msec 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 are 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~. In
order to guarantee 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
i8 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 specified condition. (ThiS word is usually something
like 'l'1'YBRK for a user I s teletype ~ It is poss ible, 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
1
Word lesl than or equal to 0
2
Word greater than or equal to 0
3
Word les8 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
(')

"-/

Special: address

dead

running
BRS 31
BRsl06
executive BRS
BRS 109

4
5

11
12
An

Bit 1 of word i8 1 (buffer ready)
Word less than zero

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.

active program (1.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.
QTI
QIO
QSQ

QQE

There are four queues of dismissed programs.
programs
programs
programs
programs

dismissed
dismissed
dismissed
dismissed

for
for
for
for

In order, they are:

teletype input/output
other I/O
exceeding their short quanta
exceeding their quanta.

Programs within the queue. 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 scheduler then begins at QTI and
scans through the queue structure looking for a program whose activation

the end of the appropriate queue.

condition is satisfied.
----------

When one is found, it is removed from the queue

structure and turned over to the swapper to be read in and run.
are no programs which can be activated the scheduler

simp~

If there

continues

scanning the queue structure.
Programs reactivated for various reasons having to do with forks
(interrupts, rubbuts, panics) are put onto QIO with an immediate
activation condition.

They therefore take priority over all programs

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.
When the phantom user is activated by (b), it runs around the system checking
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~eeding

normally.

Details of this procedure

are described in sections 9 and 7.
If the phantom 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 80me activity which it wants to carry out more or
less independ.ently of any user PAC table entry: test.. for tape ready (on
rewind) and card reader ready, and processing of rubouts (an interrupt routine
kind of activity, but too time-consuming).
activation condition.
user queue.

~~~--~---

The second word ot' ttle entry is the

PUCTR contains the number of entries on the phantom

Pointer to next entry

test number

routine address
11 12

PACPl'R for user

parameter for
routine

CJ
Phantom user queue entry

3-1

3.0 Forks and Jobs

3.1 Creation of Forks
A program may create new, dependent, entries in the PAC table by
executing BRS 9.

This ERS takes its argument in the A register, which

contains the address of a panic table, a 7-word table with the following
format:
Program counter
A re~ister
B register
X register
First relabeling register
Second relabeling register
Status.
The statuI word

may

be:

-2

dismisse.d for input-output

-1

running

t',',

di.missed on·rubout or BRS 10

dismissed on illegal instruction panic

dismissed on memory panic

The panic table address must not be the same for two forks of the same program,
or overlap 'a page boundary.

If it is, BRS 9 :Ls illegal.

The first 7 bits of

the A regiate. have the following significance:

make fork executive if current program is executive

set fork relabeling from panic table.
relabeling

propagate rubout assignment to fork (see ERS 90)

make tork fixed memory. It is not allowed to obtain a.ny more
memory than it j.B started with.

Otherwise use current

DOWN

i'"

ACROSS

....

4'rI-

5· ...

t....

3·

7. r-'

I-

('"

10
0

lL
8.

I-

't.

10.

-0

i'"'

9·

6
0

'---

Hierarchy of Processes

I·

3-2

4.
5·

make fork local memory. New memory will be assigned
to it independently of the controlling fork.
make fork ephemeral memory. Memory that it acquires
will be released when the fork terminates.
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 panic 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 fram
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
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:
ERS

44.

3-3

BRS 30.

reads the current status of a subsidiary fork into
the panic table.

It does not influence the operation

of the fork in any way.
BRS

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

II/

put into X.
BRS 32

causes a subsidiary fork to be unconditionally 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 i8 not that of a panic table for some fork.
BRS 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

.j"rnnp with the contents of the status word.

BRS 31 returns the panic table

address in A.
BRS106

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.
BRS 107

causes BRS 30 to be executed for all subsidiary forkS.

BRSloB

causes BRS 32 to be executed for all subsidiary forks.

3-4
2)

If interrupt 3i8 armed in the controlling fork, the termination

of any subsidiary fork will cause that interrupt to occur.
takes precedence over a BRS 31.

The interrupt

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 fork. 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 Memo;rAoluis1t1Gn
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.
memory panic (see below) is generated.
panic is also generated.

If the fork is fixed memory, a memory

Otherwise a new block is assigned to the fork so

that the illegal address becomes legal.
block is always asSigned.

It so, a

For a local memory fork, a new

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 1s 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.

3-5

If a fork with non-zero Rn is encountered, its Rn is propagated
downward to all the forks between it and the fork causing the trap.

any fixed memory fork is encountered before a non-zero Rn is found, a
memory panic occurs.
This arrangement permits a fork to be started with less memory than
its controlling fork in order to minimize the amount of drum swapping
required during its execution.

If the fork later proves to require more

memory, it can be reasSigned the memory of the controlling fork in a
na.tural way.

It is, of course, po as ible to use this machinery in other

ways, for instance to permit the user to acquire 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 cause a fork to be
terminated are listed in the description of the status word above.

When any

of these conditions occurs, the PACT entry for the fork being terminated is returned
to the free program list.
in the controlling fork.
it too is terminated.

The status of the fork is read into1ts panic table
If the fork being terminated has a subsidiary fork,

This process will of course cause the termination of

all the lower forks in the hierarchy.
The panic which returns a status word of zero is called a program paniC
and may be caused by either of two conditions:
A) the ruboutbutton on the controlling teletype is pushed.
terminates some fork with a program panic.

This

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.
!,

When a fork is terminated
J

in this way its controlling fork becomes the,one to be terminated.

If a user

fork is tenninated by rubout the telepype input buffer is cleared.

If the

controlling fork of the one terminated is executive, the output buffer is also cleared.
If the fork which should be tenninated by rubout has armed interrupt 1,
this interrupt will occur instead of a termination.
not be affected.

If there is only one fork active, control goes to the

location EXECP in the executive.
user.

This consideration is of no concern to the

Executive programs can turn the rubout button off with BRS 46 and turn

i t back on with BRS

47.

A rubout occurring in the meantime will be stacked.

A second one will be ignored.

()

The teletype buffers will

A program which is running with rub out turned off
BRS 26

is said to be non-terminable and cannot be terminated by a higher fork.
skips if there is a rub out pending.

If two rubouts occur within about .12 seconds, 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 tork 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 fonner 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.
provides a count in the A register.

This may be done by BRS 73, which

A scan is made upward through the fork

structure, decrementing this count by one each time a fork is passed.
the count goes to 0, the scan is terminated and all forks passed by are

When

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) N8chine instructions which are privileged
2) SYSPOPs which are forbidden to the user or which have been
provided with unacceptable arguments.
It interrupt 2 is armed and the fork is executive, interrupt 2 will
occur inltead 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 o'f the system, from
the syatem' 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 .everal tables indexed b:r job number. These are shown
on pace 3B, and indicate more or less what it is that is specifically
associated with each job.

c)
TSDA

drum address of TS block

TTNO

teletype associated with this job

ETTB

amount of CPU time used

DBA

drum blocks available

QUR

time left in long quantum

Job Tables

4-1

4.0

ProFam Inte~t.

Atacility i8 provided in the monitor to simUlate the
exi.tence of hardware interrupts • There are 20 pos.ible interrupts;
four are reserved, for special purposes and 16 are available to
the programmer tor general use. A fork may arm the interrupts
by exeouting BRS 78 with a 20-bit mask in the A register. Thi.
causes the appropriate bits in PIN to be set or cleared according
to whether the oorreapond.ing bit in the mask i. 1 or O. Bit 4
of A oorreapond.l to 'interrupt number 1, eto. No other action is
talten at this time. When an interrupt occurs (in a Dlanner to
be de.cribed) the execution of an SBBM* to location 200 plus the
interrupt number il s~ulated in the torkwhich armed the interrupt.
Note that the program counter which ia stored in the case is
the looation ot the instruction being exeouted 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 risbt thing in allcal.a including interrupts out of inputoutput instruction••
A fork may generate en interrupt by executing BRS 79 with
the num.ber ot 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 (1.e., to its ancestors). The first fork
encountered during this scan with 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 lOP. otherwise, it skips on return.
Interrupts 1 and 2 are handled in a special way. It a fork
aru interrupt 1, a program panic (BRS 10 or rubout button) which
would norma.ll.;v' terminate the fork which bas armed interrupt 1,
will inatead cause interrupt 1 to occur, that is 1 will cause

4-2

the execution of an SBRM* to location 201. This pe~its the
programmer to control the action taken when the rubout button
is pushed without establishing a fork specifically for this
purpose. If pushing the rubout button causes an interrupt to
occur rather than te~inating a fork, the input buffer will not
be cleared.
If a memory panic occurs in a fork which has armed interrupt
2, it will cause interrupt 2 to occur rather than terminating
the fork •.. If an illegal 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, when any subsidiary fork
te~inates. Interrupt 4 is caused, if armed, when any inputoutput condition occurs which sets a flag bit (end of record,
end of file and error conditions can do this).
Whenever 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
BRS

49.

5-1
5.0 The Swapper and Memory Allocation
Pseudo-relabelins
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 pseudorelabeling 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 (:R4T) and
is held in the job's TS block. Each of the 64 entries in PMT
has the following format:

H:i~ I~ I~ [
~

EX
RO
SH
EP

2 3 4

drum address

I pI
17

Process must be executive to reterence the page.
Read only (attempt to store will generate a trap).
Shared.
Will be destroyed when DOt 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 (00) into the new IMT. 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 maximum of (64 - BCMEM) private pages.
When a program is run, his TS blook is swapped and its
pseudo-relabeling registers (in the PACT table) are used to
read out the proper bytes from FMT and construct a list of
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
roam for these which must be read 1u. 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 blocks. In the course of optimizing the drum
commands, the swapper may skip a sector. If this is the case,
it searches through the memory 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 pseudorelabeling and constructs a let 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 pseudorelabeling registers into A and B. BRS 44 takes the contents
of A and B and puts them into the current pseudo-relabeling
registers. An executive program may set the relabeling registers
in arbitrary :t'uhion by using this instruction. A user program,
however, may add or delete only blocks which do not have the
executive bit let in PMT. 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 allowed to adjust those portions of his pseudorelabeling 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

TPe memory allocation algorithm 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 4.
The PMT entry for the block is removed and in any other fork
which has this PMT byte in its relabeling, the byte 1s cleared
to O.
Equivalent to BRS 4 is BRS 121, which takes a pseudorelabeling 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 particularly for the Exec 'RECOVER FROM FILE' operation. If A is 0,
BRS 120 aSSigns a2K page and skips; this operation is not execonly.
Shared Memorl. The system maintains a table called the shared
memorl table (SMT) which describes all the memory which can be
shared between jobs in the system. All the common subsystems
occupy pOSitions in SMT, and lome part of SMT is copied into
. each job's rtrl' permanently. To run a subsystem, the exec must
determine if the subsystem map is already in PMT (whioh it will
be if all. the bytes are below NCMEM) and, if not, arrange for
the bytes to be put into M.
The exec makes an entry in SMT by executing BRS 68 with a
byte number 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 b~e of·a user's P.MT and the byte number is returned in A.
The read-only bit in the SMT entry is propagated to the P.MT
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 0 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:1,t is set, the block is available. When
the user's memory is acquired, it is written as nearly as possible
'. in adjacent blocks, so that it may be read in without undue drum
latency time. Rotational positions are chosen by adding, mod 8,
the user's job number to the !MT 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, malte 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:

Drum
Address

Core
Address
l8

F :: Free entry

5-'

---\
C)

The core addre~s field of' DHTindexes two tables called the
real memory table (RMT) 8.I1d the real memory use count table (RMe).
An RMC e~tr,y 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-negat4~ RMC will be used by the swapper.
The f'ormat of an RMT entry (one per real page) is
,

4 5 6
2
0

R 0

;~"

9 :LO

R R W R

23
address of DHT entry
responsible

T I I
y P P T

RIP - drum r.ead in progress
DIRTY - .Page has been modified WIP - drum write in progress
ERRBIT - drum read error

There i8 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 fran the pseudo-relabeling
with which the swapper was entered tben have bit 1 turned on.
Tbeblocks with lowest RNA are sel.~4 for swapping out; of

coune, the1r 111.: eV't" ....
. . lJtO

Ie. . ~.tIe

. . . . . . a ....'U.,. _

be . . . .1". •

real. •• "'7 tables aDd tor each

.....

ot . . .tlou: It tb.e paae

il not d1rty, the EMT/SMr 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 d.ruJrl 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 BRB 81 with the number of milliseconds
for which he wishes to be dismissed in A. At the f'irst
available opportunity atter this. time has been exhausted, his
program Will be reactivated. This feature is 1m;plemented 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 BRB 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 BRB 88. This number
is set to 0 When he enterl the system and increments by 1 at
every 1/6othsecond clock interrupt at Which his program is
running •.
To obtain the· data and time, be can execute BRB 39. This
puts six 8-bit character.s into AB •. TheBe ohara.oters conta.in,
in order, the year, month, day, hOUJ! (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 i8 terminated by executing BRS 109.
A program can test whether it is executive or not byexecuting BRS 71, Which skips in .the f'ormer case.
An executive program can dismiss itself' explicitly. See
Section 2.
There are sOlle operations designed for so-called executive
BRBs, which operate in user mode with a map different from the
one they are called trom. BRS lllreturna from one of these
.
.
BRSs, tranlm.1tt1ng A, B and X to the calling program as it finds
them. BRS 122 simulates the addressing of memory- at the location
spec ilied in .It.. If new memory- is ass igned, it is put into the

I
I

I
·1

6.. 2

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 iy X.
An executive program can cause an instruction to be executed
in system mode by addressing it with EXS.

7-1

1.0 Teletzpe

Xsgut~Output

We begin with an outline ot the implementation of the
teletype operations. This may serve to clarify the exact disposal
of the oharacters whiob are beiq read and written. Every
teletype bas attaohed to it a table which i8 shown in Figures
7A and 7B,' No bufter. are attached to the teletype unless
input trom. Or output to the teletype is taking place. As
characters are output by the program.~ buffers are attaohed to
the teletype •. These buffers are released as soon as they are
emptied by the teletype intertace. On input butfers are attaohed
to the teletype as characters are received trom the teletype,
and they are released &SIOon as the program empties them.
Input and output bufters are logically and physioally
independeo.t, although they come out of the same buffer pool.
When a oharaoter i8 typed in on a teletype, it is oonverted
to internal torm and added to the input buffer unless it is
rubout on a controlling teletype. The treatment of rubouts
i8 d1.oussed in Seot10n 3. The echo routine address is then
. obtained trom TTYTBL and Called. It figure. out what to echo
and whether or not the oharacter is .. break character. The
ava1lable choices ot echosand break characters are listed
below. If the oharacter i8 a break character I and i f a user's
program haa been d1am1lsed for teletype input, it will be
reactivated regardless of the number of words in the input
buffer. In the absence of a break oharacter, the user's program.
is reactivated only when the input buffer is nearly full.
If tbeteletype is in the process of outputting (TOB2 > -1)
then the character to be echoed i8 put into the last byte of
the butter word which contains the input character. When the
charact.lr 11 read trom the bufter by the program~ the echo,
if &Q1, will be seneratld. Thi. mechanism, called deferred
echo;ns, perm1ts the uaer to type in while the teletype i8
outputting without having hi8 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. 0 is a routine in which the
echo for each character is the character itself, and all characters
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
M

(teletype character input)

i8 used. This SYSPOP reads the character from the teletype
input butfer 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

TOO

(teletype

~haracter

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 blan.k character. The next character will be taken al
a blank count, and that many blanks will be typed.
The TTlTlM cell in the teletype table is let to the current
value of the clock whenever any teletype a.ctivity (interrupt
or output SYSPOP) occurs. The top bit is left clear unless the
activity i. a rubout input. This cell is checked by the
rubout processor to determine whether the rubout should reset
the job to tbe exec. See p. 3-6.
Every teletype in the system is at all times in one of
three Itates:.
a) It may be the controlling teletype of some user's program.
It sets into this state when e. user enters on it.
b) It may be attached to some user in a. manner about to be
. described.
c ) It may be canplete ly free.
The Itatus of the teletype is reflected by the contents of' TTYASG.
There are mech&Dilm. to be described by which the user may direct
outpUt to any teletype in the system which is willing to accept
it and receive input fran any teletype which is not free. If',
however, be 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
'i!7
If the indicated teletype is free, it is attached to the user whoae
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 lay that a teletype ia attached
to a ulereven if it is the controlling teletype.
To release an already attached teletype, execute the
instructions
L'DA

BRS

=teletype number

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 becames 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 tor 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 1s governed by the accept
measages bit, ,the latter by the accept input bit. The accept
message bit controls execution ot OST instructions and the setting
ot teletype output ltDkl. The accept input bit controls e~ecution
of STl instructions and the setting of teletype input links.
To set these bits, the user may execute
LOA
-teletype number
LOA
Br.rS
BRB
~
The last bit ot Br.rS will set the accept input bit, the next to
last the accept messages bit. Setting or clearing these bits
will not aftect any teletype ltDks currently' active.
To do input and output to specified teletypes (rather than
implicitly' to a controll1nc teletype as in Tel and TeO) the
SYSPOPs IST and OST are available. To input a character trom
a specitied teletype, execute the instruction
lST
-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 specitied teletype, execute the instructions
LOA
-character
OST
-teletype number
(output to specified teletype)
This instruction is illegal it the tollowing three conditionl
are sati.tied:
(1) The .pecified teletype is not attached to the user,
(2) The specitied teletype does not have itl acoept meslages
bit let,
(3) The program executing an in.truction is a user rather
than an executive program. If these condition. are

7-5

satistied, an illegal instruction panic will be generated.
liote that attached teletypes do not have the same statu. as
the controlling teletype for a user. In particular, pushing the
rubout button on an attached teletype Will have no effect.
The instruction
om
-teletype number + 1000
is exactly equivalent to
IST
The instruction

=teletype number.

-teletype number + 2000
18 exactly equivalent to
OST
=teletype number.
This mechanism permits the user to do I/O to specified teletypes
within the framework of the sequential file machinery.
The user has con.iderable control over the state of the
teletype buffers for the teletypes attached to h:lm. In particular,
he may execute the following BRS' s. All the.e talte the teletype
number in X. Recall that -1 may be used tor the controlling
teletype.
BRa
11 clears the teletype input butter.
BRS
29 clears the teletype output butter.
BRS 13 skips it the teletype input butter i8 empty.
BRS
14 waits until the teletype output bufter il emptyBRS ·138 waits until a process gets dismis.ed because
the input bufter 1s empty.
,
There 18 one additional piece of machinery which permits output
to go to a teletype other than the controlling teletype. This
machinery i. implied by the top bit. of TTYTBL, which specify
whether any link bits are .et. Associated with each teletype are
two words called the absolute input link control word (LeW) and the
absolute output LOW. Each of theae words contain. one bit for
each teletype in the system. If the bit tor teletype m il Bet in
the input LeW for teletypen, .very character which goes into n's
input bufter will also go into m'. input buffer. If' the bit i8
set in the output row, every character which i8 output to n,
including echoes, will also be output to m.

7-6
Allo assooiated With each teletype are relative LCW's tor
input and output. The bitl inth••e LCW'I are set by BRS 23. Each
time any relative ICW is changed , the absolute LOW's are all
recomputed. The Boolean matrix formed by 'the absolute input
(output) ICW's 1s the infinite product of the matrix of the relative
input (output) LCW til.
The instructions
LUX
=teletype number
LDA

-TABLE

LDB

CTL

23
will let ODe ot the relative LOW' ••or the indicated teletype.
TABLE is the address ot a list of teletype numbers terminated
with -2. The bits ot CTL are interpreted as follows:
O o - o u t p u t LCW
l=input ICW
o-clear all linkl first
1
1-40 not clear 11nk.1 first
o-set link bits for teletypes WhOle numbers
2
are in the table.
l=clear link bit. for teletypes whoae numbers
are in the table.
Fran the old relative LeW and the information supplied by BRS 23
a new relative LeW i. created. New absolute LOW'.s tor aU
teletypes are then computed.
An output link can be set up between two teletypes only it
each of the teletypes satiafies at least one of the following
BRS

conditions: .
a) It i. the controlling teletype of the program executing

C··)
./

b)
c)
d)
An input

BRS 23
It i. attached to the program
It. accept ..slage8 bit il on (destination only)
The fork executing the BRS is executive.
link can be set only if the same conditions are satisfied

for the accept input bit .

7-7
To

clear all links, input and output, to or from a teletype,

execute
LDX
BRS

=teletype number
24

Special provision is made for reading 8-bit codes from the
teletype without sensing rubout or doing the conversion trom
ASCII to internal Which is done by Tel. To switch a teletype
into this mode, execute
LDX
LDA
BRS

=teletype number
=terminal character + 40000000B
.12

This will cause each 8-bit character read trom the teletype
to be transmitted unchanged 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 s~late teletype input, the operation
STI
=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
aTO
=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 teletYl*- number in X. H bit ¢ <>f A is 1,
the NO bit will be set; otherwise, the NO bit will be cleared.

C)
TELETYPE SYSTEM POINTERS,
TTYOB
TTYOBC

Pointer to next available buffer in buffer pool
Count of a'V"ailable buffers in buffer pool

N N A
S 0 P

TTYTBL

TTYBRK

S S I
I

0
L

A A A
K I M

address of echo routine 23

Waiting for break character when -1
TTY Status
PACPTR

TTYASG

of fork to terminate on rubout
3

active
inactive

Iltl controlling job 23 attached

ROLCW

RIICW
TTYTlM

TTYDEV

Relative output link control word
Relative input link. control word
R
B

value of clock when last action occurred on this tty

device (normally physi,cal teletype) using this buffer,

NS = not linked or 8-level
AM = accept message
IL = input linked
Ot = output linked
NO :: don't output to TTY interface
AK :: accept input links

AI = accept input
SI = 8-level input
SO = 8-level output
RB ~ last action was input of rubout
AP :" accept .output links

TELETYPE TABLE

TIS2
TIS4

number of characters in input buffer
next available space in input buffer (pointer)

23
WORD ADDRESS

bits 7 and 8:

TIS5
TIS6

C)
TIBBl
TIBB2
TIBLC
TOS2
TOS3
TOs4
TOff)
Tos6
TOBBl

TOBB2
TOBLC
TTYPN
TTYLN

byte 1
byte 2
byte 3

next filled space in input buffer (pointer With same format
as TIS4)
deferred echo byte count. Input characters are echoed when
the NO bit is set in TTYTBL and this count goes negative. It
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 u1 multiple 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.

C)
TELETYPE BUFFERS

TTYOC

[

~'I

2
1.

1-----1

3
t------4

1------1

BUFFER POOL POINTERS

TOBBl

C)
1.

TOBB21

)

Tos41

3·

lXl= byte count in word
N = word displacement in buffer.

PROGRAM OUTPUT BUFFER POINTERS

lXl

1.+N

I TO~ IlXl

3.+N J

8-1
~.o

Drum and Buffer Organization; Devices

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 coumand 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 onehalf 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,
wllieh is always the first entry in the job's PMT. 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 files 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 apace actually used is a
function of the device attached to the file. In all cales 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 1s in its dormant state, both words point to
the first data word of the buffer. Whenever any physical 1/0
operation i8 completed, the first pointer contains the address
of thiS word.

B-3
B.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 BB 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 s~ultaneously;
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 i. 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
nec,e·ssary 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 time for an operation; the swapper u.es this
number to decide whether it 18 worthwhile to swap the
user out while it is taking place.

Ci
pOinter to first data word in buffer
pointer to last data word
I"""

1st data word

·
··

··

256th data word
a)

layout of a file buffer

()
¢

drum address of data block, or

·
···
·
···
·
·
t

drum

address of data block, or

BFP

pointer to next index block

BBP

pointer to previous index block

BDS

log 2 (data block size!256)

BLX

file length

BCK

check sum
b)

format of an index block

data block

(\
()

:i)EV'tlord or
character I/O

0 f

CHI nru.f IRX I~

~ \~ I~ I

BUFS
buffer size

RX random access
BF requires buffer

max. unit number

output

: physical. record size

W buff'er

OUT

BC not common (i.e. don't set DIU)

()

bl.ock I/O routine

GP\'f routine

U check unit number

BDEV

l.~

I IW1l1our I~ I

CH char oriented
DRM drum

routine

J
~

BIO routine

DIU
device in use

1
OPrIDEV

opening routine

f'il.e number using this device or -1

u=o

points to ADID (has unit number added)

U=1

3
expected wait tiffie
Lll cl.ock cycles
EO

opening subroutine

exec only allowed to open

DEVICE INDEXED TABLES

)
,~-.-

..-----"""------- ----"""------"""""

-----

---

9-1

2.0

Se~uential

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 l4p
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 userts 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 userts access to an open file is housekept by means of
a position pointer to the file. This pointer may be moved
explicitly 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. CIO 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
accel. il intended to implement append-only files. You may not
move the pointer or perform random operations unless you have
position access to the file.

9-2
file opened as
sequential input
sequential output
random read-only
random read-m'i te

access given
r

The mechanisms for setting the length, data block lize,
or for moving the pointer are described under BRS 143-144.
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 traoe of
the tile~ Use of this BRS is limited to the EXEC.
BRS 143 1 144 have been implemented as general .read and
set statuI of a thingy. The oalling sequence is; .
A: table address or data (depends on ~)
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 l-ll: "type" of thingy
bits 12-23: "attribute"
"type" is .1 for a drum. fl1e, 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 D.its are the current word pointer, the top
two the character offset. (~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 Ilo mode) The sequential Ilo operations (CIO,
WIO,BIO) are interpreted as input if the sequential mode 1s
~, output if the mode is 4B7.

9-3

C=)

(Capabilities) Opening a file may give read/write/position
access to the tile. These bits may be read in bits 21-23.
It you try to set them, they are ANDed with the existing
capabilities.
,. (Data Block Size) Returns n where 2n+8 is the. number ot
words in a data block. May be set only if the tile length
is p.
6. (User words) Eaoh tile in the system has tive arbitrary
word a aaaociated with it. Anyone may read'them but only
the exec may set them.
7. ( "structure") A tile may have voids in it. It you are
interested, you can find out where theae are. BRS 143
returns the number of worda trom the current sequential
pOinter to the next transition. It also moves the pointer.
If you are oroa.ins a void part ot the file with this
operation, the Sign bit of the number is turned on. Setting
thia state with BRS 144 is interpreted by releasing this
many warda beyond the pointer. This also move. the pointer.
8. (count data) Can only be read. Sets the pointer to the
beginning of the tile.
9. (copy the index block) Can only be read. Give.s a copy ot
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. (PMT) Reads the private part of lMT.

9-4
The Exec opens a sequential drum file by the following
sequence of instructions:
LOX
LOA
BRS

C~)

=device number, 8 (input) or 9 (output)
=unit number, address of first index block
1

If the file is opened successfully, the BRS skips; otherwise,
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 1 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 1 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 inhibits opening of output
files only.
See Section 9.2 for other error conditions.
BR~ 1 returns in the A register a file number for the file.
This file n~er 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 programs, user programs should use BRS 20 instead.
To close all, his open files an executive program m~ execute
BRS 8. The oorresponding operation for normal user programs is
BRS 17.
Three kinds of input~output may be done with sequential
files. Each of t~ese 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
:files.
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 0 and 8 or 7 in the file number (these are called
--------~!1!i~) 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 recor~ 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-tile condition occurs on the next input operation
after the end of record, which signals the last record of the file.
The user m~ generate an end of record while writing a tile by
ul1ng the co~trol 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
LOA
=-number ot' words
BIO
=£ile number
should be executed. The contents of A and X will be destroyed.

9-6

The A register at the end of the operation contains the first
memory location not read into or out of.
Ii' the operation causes any of the fla.g bits to be se't, 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 ~lY 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 j.n 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 BRS 63 (vide infra).
The index block for a sequential drum file contains one
word for each p~VBical 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

1_ _ _ _ _ _ _ _ _ _ _ _, . -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __

9-7

returned in A as usual and the index block. number in X. The
initial settings of the r, w, and p capabilities, and the
lequential I/O mode flag, should be given in B.

To read an index block into core
BRS

may 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

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 BRS 1, except for the device number.
Available device numbers are
Paper tape input
1
Magtape input
4
Magtape output
5
6
PDP-5 link input
PDP·5 link output
7
The device number is put into X. The unit number, if any, 1s
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
Tape file protected (output only)
1
2
Tape reserved (see p. 9-8).
BRS 1 also accepts the following three character mnemonics
instead of' the device numbers. Either the rlame or. the number
goes in X tor the call.

9-8

1
2

4
5
6
7

8
9
10
11
12
13

14
15

Ml'I
MTO
PDI
PDO
FSI
FSO
FIL
LPO

MDI
MOO

paper tape input
paper tape output (not available)
card input (not available)*
mag tape input*
mag tape output*
PDI5 input
PDI5 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

19
20

CSI
CSO
TTl
TTO
NON
lOS
SNP

requires executive status

PrI
PrO
CDI

nothing
subroutine file
snooper counters (Berkeley only)

ms 1 is inverted by BRS 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.
LOA
CTRL

=1 (end of record)
=file number

is available for physical sequential file 5 (magtape output).
Several other controls are also available for maptape files only.

9-9

These are:
2
3
4

5
6
7
8

backspace record
forward space file
backspace file
write three inches blank tape
rewind
write end of file
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 prograDl may arrogate a tape unit to itself by
putting the unit number in A and executing BRS 118, which skips
11' the tape is not already attached to some other job. BRS 119
releases a tape so attached.
It i8 possible for magtape and card reader files to set
the error bit in the tile number. The first I/O instruction
after an error condition will read the tirst word of the next
record--the remainder of' the record causing the error is ignored.
The magtape .routinea 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
wnether a W-butfer 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 drastio action;
it can be used if a program is aware that the W-buffer i8
malfunctioning.
Direct tape I/O package. A mechaa1am for accessingarb1trarily
formatted mag tape 1s available. ~he appropriate operations are:
BRS 1
open
BRS 2
(or 17 or 2P) close
BIO
block input/output
CTRL
control

9-10

BIO is used in the nor.al way, with a word count in A and core
address in X. BIO will not live 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 tne 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 implemented to allow the user to set the mode
for the tape. This operation takes a ~ .or 1 in B21 for setting
the tape in odd or even parity. (TSS tapes use odd. pa.rity.)
B22 and B23 contain the. "trame 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 lettjustified. The word count for transfers covers the numbers of
words in core actually used. When the tape is 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 BRS 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.

o
i

9-11

9.3 File Control Block!
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

o
Drum

files
only

9.4

0
0

0
Cl

7 r~

first index block address or 0
subroutine address
15 10
C
C2

normal file
subr. files
23

IC D R R
H F X D

0
U
T

device

0 0 0 0
0 0
0 2 3 job B 9
drum buffer address or 0
char number
0
count 0
busy count (-1 it file not busy)

normal file
subr. file

Cn .. word being packed or unpacked
char count .. -1 to 2
OR .. character oriented
OUT .. output
DF • drum tile
RX = random access
{ RD = read only
ERR • error
Permanent~

Open Files

There are a few built-in sequential files with fixed file numbers:
o
controlling teletype input
1
controlling teletype output
2
nothing (discard all output)
. input from teletype n
1000+11
output to teletype n
2ooo+n
These rile. cannot be ol,ened and need not 'be closed.

10-1

10.0 Random Drum Files
A random drum file is identioal in physical struoture on
the drum to a sequential drum file. The only major differenoe
is that the non-zero words of the index blook are not neoessarily
compact. The reason for this is that information is extraoted
from or written into a random file by addressing the speoifio
word or blook of words which is desired. From the address whioh
the user supplies, the system extraots a physical block number
by dividing by the data 'block size and a looation of the word
within the block Whioh is the remainder of this division.
Further division by 144 yields the appropriate index block. A
file may have any number of index bloc~s.
A random file may be opened by using BRS 1 with a devioe
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 I/O
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 instruotions
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 1nput-outp~t to random files is also possible. To
input a blook, exeoute the instruotions:
LDX =first word address .
LOA =number of words
LDB -first address 1n file
DBI -rile number
To output a block of words to a. random fHe, 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, &8.i8 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 !lli.. To do thi.s,
execute the instructions
LDA
=file number
BRS

The specified file remains the secondary file until another
secondary memory file is defined or until the file is closed.
To access intormation in the secondary memory, two SYBPOPs 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
IAS
address
should be executed. To store a word from A into the secondary
memory, the ins'cruction
BAS
address
should be executed. The word addressed by either one of the.se
SY8POPs should contain the drum address which is to be reterenced.
This word may also have the index bit set, in which case the
contents of the index register will be added to the contents
ot 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 similar to the mechanism for allocation of core
memory. Whenever the user addresses a section of a random
drum tile which he has not previously used, the necessary blocks
are created and cleared to O. Note that the user should avoid
unneoessarily large random drum addresses, since they may result
in the crea.t:i.on of' an unnecessary number of ind.ex blocks. To
relea.se 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 allows the user to acquire

2K pages on the drum. and read. or write on them directly.

This

space is ass igned from the swapping area on the drum and referred
to directly by its drum address; a bit table private to the user
is used tor validity cheoking.
To acquire a 2K page, execute
BRS

126

with the desired angular position on the drum ot the page to be
assigned in the bottan bits of A.
BRS 326 returns without skipping.

If' no more spaoe is available,

otherwise, BRS 126 skips and

returns, in A, the drum address of a 2K page as a word address
(1. e. , with the bottom U bits zero).

A page may be released by

putting this address in A and performing
BRS

127.

To release all pages acquired in this manner, execute
CLA

BRS

This is done automatically by the RESET canmand in .the executive,
as well a8 by RECOVER and by a oall for a new subsystem.

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
LDB

LDX

c::

=core address
=drum. address
aword cO'U;nt
124
to read'\.
1~'5
to write]

,10.4
These BRS'. preserve all the central registers and normally skip.
A no-skip return,tadicates an uncorrectab1e 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 aSI1gned to the user via BRS 126.
(The latter restriction does not apply to executive programs.)
2) The transfer must not cro.1 a 2K page boundary either
in 'core or on the drum.

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 inputoutput 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 inputoutput is done, simply by changing the file from aphysical.to
a subroutine file. A subroutine file is opened by executing the
instructions
LDX
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:
Character input subroutine
11000000
Character output subroutine
11100000
Word input subroutine
01000000
Word output subroutine
01100000
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 o·peration on the file is performed,the
subroutine will be called. This is done by simulating an 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 regi.ters are transmitted from the I/O SYSPOP to the
subroutine unchanged. 'llhe contents of the A register may be
changed by the packing end unpacking operations necessary to
convert from character-oriented to word-oriented operations or
vice versa. The I/O subroutine may do an ar'bitrary amount of

c.)
"

computation any m&¥ call on any number of other I/O device. or
other I/O subroutines. A subroutine tile should not call itself
recursiveJ.,y.
When the subroutine i. ready .to return, it should execute
BRS 41. This. operation replaces the SBRR which would normalJ..y
be used to return from a subroutine call. The contents of B
and X when the BRS 41 is executed are transmitted unchansedback
to the calling program. The contents of A may be aitered by
packing and unpaoking operationa, A subroutine file. i8 cloled
with BRS 2 like any other file.
In order to implement BRS 41, it 1s necessary to keep track
of which I/O subroutine is open. This informati.on is kept in
s1x bits of the PAC table. The contents of these s1x bits 18
transferred into the opcode field of the return addre.8 When an
I/O subroutine is called, and is recovered trom there When the
BRS 41 11 executed.
The u.er should be warned that a .ubroutine tile should
not be uled b1 a program in a different address apac, from the
.ubroutine it.elf. In particular, subroutine fil•• may not be
given to the BRS. which involve accce.1 to named files (de.cribed
in the next section).

12-1

12.0 File Naming System
Because of the possible conflicts which may ari.se 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 pr~ary 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 asa 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 1 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
- The information has the form of an assembled,
but unloaded program.
3. Symbolic - The informat ion is of a form which can be
readily listed on some printing device.
4. Dump
- Comprises all the information in memory
necessary to restart the user from his
ctITrent 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 tile name is
NOTHING
which al~s contains precisely nothing and whose function is to
aot as an intinite sink in which limitless unwanted output can
be lost.
A commoner source for symbolic files is the output trom
some subsystems, notably the text editor, ~D.
Type 2, binary tiles normal.ly arise as the output from the
machine-language assembler ARPAS.
Until the actual process ot output from the subsystem occurs,
identification ot 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 ot a
similar kind, some explicit identification must be attached to it.
12.1 File

N~i~

The names which the user is tree to invent and assign to
files are of two types:
1. Permanent names
2. Scratoh names
Scratch names differ trom 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 tile.
As p8l'11anent 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 fram all others currently defined by the user. This
means that a new name can never be introduced in its unquoted
form. A quoted name, on the other hand, is always accepted in its
entirety tran the user. The initial and terminal' quotes are
then removed and the name compared with the directory of names
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 same 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 that the BEGINNER, NOVICE and
EXPERT commands apply t,(j file na'l1e recognition (see R-22,Section'.7).

12-4
12.2 Accessing other Users· Files, .special Grou12s

The naming system described is adequate to reference all
the files belonging to the current user, in whose name the exec
was entered. Ifowever, to refer to files belonging to another
user, it1s possible to augment the file name by that user's
name together with, optionally, a special accessing code called
the s,rou12 ~.
To do this the basic file name must be prefixed by one of:
( < user name > )
or
(. <: user name >, < group name > )
Thus for example:
(JONES) t FILE1'
or
(JONES, GROUP1) 'FILEl '
When such a string as the last is collected from a teletype
by BRS 15 or 16, the characters II, GROUPl r! 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 t files
is in the ha.nds of Jones himself. Jones may declare that a
member of the public at large who tries to access his 'FlLEl f .
using (JONES)'FILE1' has entire (read-write) a.ccess, read-only
access, or no access at a.ll. It is also open to Jones to
define independently a greater degree of accessibility to a
user who supplies the group name.
Specia.l 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.
BRS 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 associates with it a
number, n, in the range 1!S,.~ 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 wo~d (see BRS 48).
A user may have up to 15 currently def'ined, distinct special
groups; an attempt to define more results in a no skip return with
A=O. An attempt to define an aheady existing special group
name also results in a no skip return, but with the group number
in A.

i
I
,\

12..5

BRS 62 - Delete Special Group
Takes a special group number in A.
The associated special eroup 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 Pseudonlffis
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.

12.4 Doing I/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, l-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 which 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 I 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 sequent:i.al 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 oonveniently or efficiently accessed
in the manne~ of random files and are restricted to holding only
sequential files. However, the command 'COPY FILE' wil.l allow a
user to copy information :eran 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 bac~ to a random device. Such a "random" file on a
sequential me.dium 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 ERS 92)
to a non-sequential medium.]
12.5

Ope~ing

Input 1"iles

BRS l,5 - Open named file for input:
Take. in A a control word
in B the address of' a string pointer, or ¢
in X a dual file number.
The function of this ERS is to recognize an existing file name,
optionally, open the tile for input and return a file number for
use with iubsequent data-input commands.

12-7

Designation of the File
The string ad.dressed by B must be the complete or incanplete
name of a predefi.ned 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 determine uniquely a file name (or no such name).
If the f'ile name :1.s unquoted so that prerecognit10n 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
collectedfram the input file are not transmitted to the caller's
memory. If bit 0 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 f~le name was complete on entry (i.e., no characters need be taken fran the input file), a terminating character
must be delivered to confirm or abort the file name. Confirming
characters are those with an internal code representation 0 to
168, also semicolon, tab, line feed and carriage return; the
aborting character is 1. All other characters cause? to be
output and are otherwise 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, suppresses opening the file (no file number
is returned)
Bit 2, i~ 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 terminat1.ng character
In X, is a composite word comprising

l2A-l

TAPE or

PE~NT

FILES

WORD 0
WORD 1
WORD 2

~
TAPE SYSTEM NUMBER

WORD 3

DRUM ADDRESS

for
BRS48

Mask

~
1 :: random

SR ::: sequential or random
PRA :: private accessibility
PUA = public accessibility

1 :: rea.d only

o ::

denied to public
1 :: public read only
2 :: public read and write
SGA = special group accessibility 0 = re~ and write
1 :: read only

SGN :: special group number
0 = none
S = status
0 ::: file permanently on drum
1 =
, file on drum
2 = file'on system tape
3 = file on private tape

U • unused

SCRATCH FILES
WORD 1 .. -1
WORD 0:: 0, WORDS 2, 3 as for TAPE Fn.ES

BUILT-IN FILES

WORD 3:: -2; WORD 2 ..
a. Device
WORD
WORD
WORD
WORD

0
0 =0
1 (9 to ll] :: no. of tape unit '
1 (12 to 171 -= devtce no (O/P)

1 [18 to 23] '" device no. (I/P)

12A-2

-1

WORD 1 = creation date

PSEUDONlMS

Description Block Format

(lip)

WORD 3 [20 to 23]
group no.

WORD 3 = -1
WORDS 0,1 == string pointer to real string

(O/p)

SPECIAL GROUPS

WORD 2
WORD 0

Permanent file no. WORD 0 0
WORD 1 (6 to 11] == file no.
HORD 1 [18 to 23] == file no.

WORD 2

l2A-3

c)
FILE DmECTORY DESCRIP.rION
(A)

PREAMBLE AND STORAGE ARRANGEMENTS
0

FLTH

SGUS

ZRO
ZRO
ZRO

FDJX
FUNO
BSS

SRO
ZRO
ZRO

HTL
EHTL
FDSS

ZRO
ZRO
ZRO

EFDSS

ZRO
ZRO

4
5

6
7

()

File directory length
Address of compressed file input table (CFIT)
(Bits set to indicate special group numbers
in use)
Drum index block address for this file directory
User number
Address of beginning of description block
storage
Beginning of hash table (BRS 5 I 6 table)
End of hash table
Character address of beginning of string
storage (WCH table)
End of string storage
Garbage collection option

The remaining parts of the file directory appear in the
following order:
Hash table (HTJJ, EHTL)
String storage (EHTL, BSS)
File description block storage (BSS, CFTA)

l2A-4

USER DIRECTORY DESCRIPrION
(A)

PREAMBLE AND STORAGE ARRANGEMENTS
0

3
4

ZRO
EUHT ZRO
ZRO
BUDSS ZRO
BURT

5
6

EUDSS ZRO
ZRO
BUDBT ZRO

BUDB

ZRO

Beginning of hash table (BRS 5,6 table)
End of hash table
BRS 5,6 link
Character address of beginning of string
storage (WCH table)
End of string storage
Garbage collection option
Address of beginning of description block
table
Length of each user description block

The remainder of the directory appears in the following order:

Hash table (BUHr, EUHT)
String storage (EUHT, BUDBT)
User des,cription blocks (BUDBT, end of directory )

(B)

TYPICAL HASH TABLE ENTRY

°2l~_____________________STR__ G~~~S~~~~~T_O__________~
lN
__

(C)

USER NUMBER

TYPICAL DESCRIPrION BLOCK ENTRY
0

HTA

FDL

:PW

5
6

CTW

LTW

ZRO
ZRO
ZRO
ZRO
ZRO
ZRO
ZRO

Address of hash table entry
File, directory drum address
Maxtmum drum block allowance
Access word
Password hash code
CPU time word (6Oths of a second)
LOGm time word (seconds)

ACCESS BITS ARE

WAIT }
IDIOT

BRS 37 mode

PRFFLG

permanent file flag

3
4

XMOK

exec mode OK

NTFFLG

new tape file flag

UTTFLG

new files to user tape

OPTFLG

operator flag

l2-8

6 to
In bits 3 to
Bit 0 is set
Bit 1 is set
sequential
In bits

23, the file length

5, the file type

if the file is random
if the file is not stored on a
medium.

Error Conditions

All error conditions are followed by a no-skip return with an
indioator in X; A and B are undisturbed.
-59C~-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 (see pp~ 9-1, 9-7).
X=l This exit occurs if the name given is not a predefined
name in the specified userts file directory.
X=2 Indicates that the file name 'Was aborted by delivering
? as a. termina:t ing character.
X=O Any such error ~ls accompanied by one of' the following
'error messages' being sent to the command output file
(normally the teletype).
?

ILLEGAL USE OJ!' PSEUDONYM

-NOT PUBLIC
-NO GROUP NAME ATTACHED
-WRONG GROUP NAME
When the requested file exists on magnetic tape it is possible
to receive a.l)out 20 different error messages, most of which are
self explana:tory. The position check message, "(re: n)" means
only tha.t the tape has reset its position after becoming "lost"
and should be of no coneern.

12.6 Q2ening OutEHt Files
BaS l6 - 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.

12-9

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
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, ind:!.cate the file type.
The type of a new file j.B always set to be t.
The type of an old file is changed to t unlesst::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 fi.le. 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.

R-2l
12-10
Error Conditions
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 1 with
-~~2 (see pp.9-l, 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 DmECTORY 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, some 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 tile 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
(tromrandom to sequential or vice versa) will elicit a
meslage to notify the user before the name terminator is
delivered.

12.7 Miscellaneous File Q2erations
BRS

63 - Delete name from file direqtory
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 ERS 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,O respectively. Such an exit results
only from an attempt to delete a drum file.
indicates an attempt to delete the last name of
X=O
B. built-j.n file.
Xcl
i.f 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
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. 12A) are skip-returned in A, B a.nd X respectively.
BRS 48 - Set file model
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 ac(!essibility of the
specified file (which mUllt belong to the caller).
All of these characteristics are determined by bits 1 to 4, and
6 to 16 of the third, "xl".ode", 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 a skip return,
failure by a return without skipping.

12.8 Qpening 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 se~s
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 pointer 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 dec1m&l digits enclosed between slashes, 5 characters
in all, (a number which exceeds 999 is taken to designate the
string /999/). This stri.ng 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·

12-13

BRS

12
Ta.kes in A a code word
in X an integer

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 DRS 16. Hits 0 to 5 of A also have the same
Significance as for BRS 16.
BRS

6.i

Ta.kes 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 t,he Pile Direotory, Some Implementation Details

File names, group names a.nd pseudonyms are contained in a
hash structure of the tYl)e described in the SeeM-on 14 of this
manua.l. The f:i.:rst 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 drum file, tape file, special group, pseudonym, etc. Notice
that severai entries in the hash table may point to a single
description bloek; the associated names are then synonyms f6r
the same object, which can be referenced by anyone of them.
The command DEFINE NAME creates a new name to point to an
existing description block; conversely DELETE NAME detaches the
name from its descrjption block, the description block itself
is lost only if' this was the only name po1nttng to it.
The format of a single hash table entry with attached file
description bloek is sketched on page 12 A.
I

12-14

C~)

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).
BRSs are BRS 60 and 48.

The corresponding

12.10 Miscellaneous Services

BRS 92 - Copy file to file
By means of this BRS information 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 unsuocessfUl, a no-skip return, possibly preceded
by a message.
On entry, the contents of A are taken to refer to the input

file as follows:
bits 15 to 23
bits 3 to 5
bit 1
bit 0

give the input file number
give
is 0
or
is 0

the file type
for a sequential device (tape, teletype)
1 for a randbm device (drum, disk)
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 ¢, 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 ) character, if and only i f the input file

c/!

b)
c)

is a teletype.
An EOF (137 ) character for ofher type 3 files.
8
2 consecutive 1;ermwords (27&57537p,) for all other
sequential files.

12-1".5

Input file random
a) 1 termword i f the file is stored on a seq,uential device.
b) Otherwise the copy terminates when the end of the
index-block chain is reached.
The return after a successful copy 1s 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 v1.ce-versa.
They are all followed by a no-skip return.
Errors of type (b) are all signalle(l by a message, which is
sent to the command output medium. The message,s may be any of:
-END OF TAPE
UNTTh1ELY EOF IN INPUT
UNTTh1ELY EOR IN INPUT

RANDOM FILE TOO BIG, TRANSFER TERMINATED AT ADDRESS

FAILED TO READ INDE.'X 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.

()

BHS

23 -

Ms.,ite a "save II 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 list
of positive numbers terminated by any negative number. The first
entry of the list is taken as a "starting address" - and is the
address to which a transfer of control will be made when the data
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 1s to be saved.

If the information
there is a skip return.
in an immediate no-skip
The formats of the
file are:

is successfully transferred to the file,
Any failure in the data transfer results
return.
core bounds list and the resultant save

!2!mat of Core Bounds LisJ:!.
Starting Address
ml
nl
~

···
~

~
negative num.ber

Format of Save File
11 == min (ml,n l )

max (ml,n l )
Starting Address

··
data· from
core range 11 to ul
12

data from. core 12 to u 2

data from core lk to ~
term word
term word

12-17

BRS 94

Restore a save file to core

Entry AlB • relabeling
X • file no. of sequential save (type 1) file
The save file, which should have the fo~at 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:

Return No Skip:
Skip:

A
B

= the
= the

desired tape position (0:"..A<2;6)
user number of the file owner (BRS 132
only)
X = the tape system number or the tape unit
number with bit 0 set.
A:: error flag (-2CLB, WCH will
write the character in A into character position CLB+l and
increment CLB. If CL~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 WCHts.

14.3 String COmpare

()

Operation.~,

SKSE ADDR skips if the string addressed by the pointer in
AD is identical with the string addressed by ADDR. 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 stringt.. rather than numbers. A, B, X
are not disturbed by SKBE.
SKSG ADDR skips if the contents of the string addressed by
AD is greater than the contents of the string addressed by ADDR
and ADDR+l. Comparison :1.8 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 string pOinter in AB; the string

14.4
pointer in core is also updated. If bit 0 of A ::i.s 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 ~ 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 a.nd the character
$ is interpreted as carriage return, line feed.
BRS 35 accepts a f:i.le number in X and a string pointer in
AB. It outputs the string to the file.

14.5 !J!I.sh Ta.ble Looltup Instruct ions
The ha.sh 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-plus-one locations
of' the hash table we shall denote by BT, EBT 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 a.rb i trary inf'orme.tion. Note, however, that
bits 0 to 7 of' the string pointer words ~ be zero if used with
Gel 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.
Bef'ore 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 5 takes a. string pointer in A, B, a. table address in X.
The table compr:lsea 1 wnrus:
ZRO
ZRO

HT
EHT

ZRO

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 "index")--and in A the string
"value"; it skips on return. If the search is unsuccessful,
BRS 5 returns with A, B unchanged and the address 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 sGanning
algorithm used in BRB , 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 (E2i 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 containing
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'. 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 E2i neoessary to use BRS 5 and BRS 6.
The behavior of BRS 37 depends on the (~omme,rld 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 found 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 2! 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 table 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 buffer
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, 2!. for no match to be possible. In the former case
the remaining 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 str1ng
pointer in ABto the string so far collected; X is undisturbed.
If a match is found there is a skip exit with the address of the
matching t_ble entry in A and the string value in B, X is undisturbed.
The following aubrout1ne illustratos a. use o·r the hash
table taa1.11ty. A .tr1n~ is input from the tel{~type. and appended
to WeH string storage unt:tl a carriage return 1s 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
DRS 5, 6. CTt is the address of a table for WCH.

LOOP

ZRO

INPL

LDA
STA

CTt

Tel
SKE

=155B

terminator?

BRU

WRITE
TEMP

yea

LDA
LDB

BRS
BRS
SBRR

WRITE

WCH
BRU

()

remember beginning of string

TEMP
CHAR

CTL
5
6
INPUT

CTL
LOOP

15-1

15.0 Float1ns POint Instructions
This section describes the floating point operations which
are available in the system. SYGFOPs are provided to do floating
addition, subtraction, multiplication and division and to convert
under format control between the internal floating point representation and an external representation as a string of digits,
decimal points and E (tor exponent). BRS' s ex1stwhich 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 Floatins Feint

~epresentat1o~

A float1ng point number is held internal.l..y as two 24 .. b1t
machine words. The format "is

f (::
"'ellD'ilr 11 a1""'11 DOrmal1zed : i.e. ~ the most aisn1f1cant
bit of the mantilsa differs from the sign bit. All floating
point operations expect normalized operands and produce normalized
reaulta. Both mantiasa and exponent are treated, as two.,. complement
numbers. The two words of the floating point number appear in
the Ai relister or in memory in the order indicated.
4 floating point DUmber i8 represented externally as a
str1Dg ot character.. This string has the following forml
[:1 rltl"lDs of digits] [.[string ot di~itBJJ [E[:]atring of digits]
The braabt•. tDd1cate optional constituents: At least one digit
must appeU'. Imbe4d.e4 blanks are not allowed. The E indicates
that the preceding number 18 to be multiplied by the power of
10 .pec1fl.4 ~r the E. In general a floating point number
being input may tllte any torm which matches the template above.
On output the form produced Will be determined by t~e format specified.

:1,5-2

10.2 Floating POint Arithmetic
There are fou~ SYSPOPs to perform floating point a~ithmetic.
Each of these taltes one operand from AB and the other from M and
M+l where M is the effective address of the instruction. The
result is lett in AB in normalized form. If its magnitude is
sreater than 5.7896Q44E+76, the overflow indicator will be
turned on and this value will be returned. The overflow indicator
is not cleared by any of theae tDltructionB. In this respect the
floating point POPs behave exactJ¥ like the integer machine
instructions: a sequence of' operations can be performed before
the overflow bit il teated. The bit will be on if any operation
caUled an overflow. If the :IIesult il less than 0.803616E-77, it
will be let to O. No indication will be given.
The four operations are:

FAD
FSB
FMP
FDV

()

Floating
Floating
Floating
Floating

add
subtract
multiply
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.
Load 'JOinter:

puts the contents of M and M+l 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
LnP M

point numbers.
Floating negate:
Fix:

c)
Float..

BRS 21 returns in AB the negative of the

floating point number supplied in AB.
BRB 50 converts into a double preciSion fixed point
number. The int~ger part appears in A.
The traction part appears, lett justified,
in B. If' the integer is too larse, the
moat significant bits will be lost. The
:i.nteger part is the next smaller integer.
~s

I.e., IP{-1.2)=-2.
51 converts the integer in A to

floating point number in AB.

Ii.

normalized

15-3

15·3 IniBt!OutEut Formats and Conventions
Every I/O 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

c··.\

Field Name

0-2

3-8

9-14

15
16-23

~_/

S1snificance
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 apecified field.
4 E format with the number left
justified within the specified field.
5 F format with the number lett
justified within the specified field.
Number of digits following the decimal
point.
Total field width
If the field width is 0, the I/O will
be done in free format.
Overflow action.
I/O file number. 0 always refers to
the te letype . ISC and SIC ignore
this f1eld.

Examples:

,6.3

30306000
21121000

E1.7 ·9
10005000
15
On input only the W and N fields are significant. Note that
exactlyW characters will 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 in,put operations always return a floating point result.
They 'ld.p unless overflow occurs, in which ca.se they return the
largest possible number and do not skip. .Any number of digits
may be provided: the first 11 digits after anY' leading zeros will
be the oneBused.
On output the W field should be made large enough to
accommodate Sign, dec±mal point, E, sign of exponent and exponent
(if thef'o:rm.a.t type requires anY' of these E!lements) a.s well a.s

15-4
the digits of the number itself. See the discussion of error
conditions belo",. The 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 characters.
If the magnitude of the number is between lEO and 1E9, 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.

5.789604462E+76

5 .379605400

15.4

C)
<'

InPqt/Out~ut

Operations

Two SYSPOPs are available to convert between the internal
binary representation of a floating point number and its
external decimal representation as a string of characters. The
string is stored and addr.essed according t,o 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. 'l'he first character after t.he number is returned
in X if free format was specified.
/
Internal to stri.ng conversion (ISC): The number :i.n AB is converted
according to the format in X and the result:lng external representation is written onto the end of the string addressed by the POP.
The string pointer is updated.
Two BRS's arc available to do input/output and conversion
at the same time:
Floating input: BRS ~j~~. Input takes pla..ce according to the
fo:rmat word in X.l'l1e operation of th:ls HRS is identical
to that of SIC.

15-5
Floating output: BRG 53. Output takes place accord.ing to the
format word in X. 'J.'he operation of this BHS is identical to
that of'ISC.

(.,

,,-)

15.5 Output Error Conditions
There are four possible error conditions. When one of these
conditions occurs the following action 1s taken:
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
Action
~

/--',

(

" - ,J

1
2

T fielq is not 1,2,3,4 or 5
Exponent field is too small

Integer exceeds 8388607
in magnitude
Field for F-conversion
too sma.ll

Assume 2(E format)
Discard characters from the
left or ta.k.e 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

(i
/

BRS TABLE

MONOPN

mMBER

MONCLS

MPl'

3
4

NAME

SSCH

ssm

5
6

DCLR

IOH
FKST

EXSOFN

9
10
11
12
13
14
1.5
16
17
18
19

CFm

FHA

LNK8

23
24

PPM

()

ClB
CET
SKI
DOB
EXGD'N
EXOOFN

UABORT
EXSIFN

LNKC
MaGS
SKROUT
ASTT
RSTT
C~B
(-

2.5
26
27
28

FUNCTION
Open file
Close file

9-4, 9-8
9-4

Release memory
SPS search
SPS insert
Release all space acquired
via BRS 126
Close all files
Open fork
Programmed panic
Clear input buffer
Declare echo table
Skip if input buffer empty
Wait for output bufter e~ty
Symbolic input file name
Symbolic output file name
Close all files
Scratch input file
Scratch output file
Close file
Floating negate
Link TTY
Unlink
Set AM and AI bits
Skip if rubout waiting (exec)
Attach TTY
Release TTY
Clear output buffer

5-3
14.,
14-5
10-3
9-4
3-1
3-6
7-5
7-2
7-5
7-'
12-6
12-8
9-2
12-12
12-12
9-2
15-2
7-6
7-7
7-4
3-6
7-3
7-3
7-'

A-2

NAME
FKRD

GETSTa

30
31
32
33

~U1'MSG

~urSTR

35
36
37

FKWT
FK'J)1

~UTNUM

GSI¢f6K
GETNUt1

RMDY

RDET

I~RET

41
42
43

RREAL
RDRL
STaL

SQ9S
NRPUT
SR~UT

SE'l'FDC

SRIR
FFIX
FFLT

FFI
F~

FUNCTION

NUMBER

44
45
46
47
48
49
50
51 ,
52
53

Read fork
Wait for fork
Terminate fork
Collect string
Output message
Output string
output number
General string lookup
Read number

3-3
3-3
3-3
14-3
14-4
14-4
13-1
14-,
13-1

Read date and time
Read echo table
Return from Ilo subroutine
Read clock
Read relabeling
Set relabeling
Dismiss on quantum overflow
Turn rubout ott (exec)
Turn rubout on (exec)
Set fd control word
Read interrupts ~ed
Fix
Float
Formatted floating input
Formatted floating output

6-1
7-2
11-2
6-1
5-2
5-2
2-3
3-6
3-6
12... ll
4-2
15-2
15-2
15 .. 4
15-5

MRSB

MBEX

56
57
58
59
60
61
62

SSMF

RFOC
SGDEF
SGDEL

Make or release resident block
Make block executive
Guarantee 16ms computing
Define secondary memory
Read PMT
Read tile directory entry
Define speCial group
Delete special group

5-4
2-3
10-2
12-ll
12-4
12-5.

A-3

NAME

NUMBER

FUNCTION

EXDEL

63
64

Delete named tile

EXSFDL

DFDL

66
67

Delete scratch tile
12.. 13
Delete drum tile (contents only) 9-4

EBSM
GBSM

smc
EXPMS

*EPPAN

12-10

'-3

Enter block in SMT (exec only)
Get SMT block to EMT
(exec o!ll1)

70
71
72
73
74

Skip it executive
Exec diami8sa1(exec only)
Economy panic

6.. 1

Arm. interrupt.
Cau.e interrupt
Make blook RO
Dismiss for specified time
Sys go

4.. 1
4-1
5.. 3
6-1

Set special teletype output
Clear special teletype output
Read execution time

7-7
7-7
6-1
3-5
13-1
12-14

Declare fork for rubout
Time to string
Copy
Save
Place

Dump

Recover

' .. 3

2-'
3.. 4

75
·76

SAm

SIIR
NBRO
'WUA.L

SET8p

cLR8P

RTEX

88
89
90
91
92
93

DFR
EXRTIM

ECCOPY
BeSAW

77
78
79
80
81
82
83
84

ECPIAC
ECDUMP
ECRECV

12-35
12-17

A-4

(~)

-NAME
ECFNDU

NUMBER

!:~CTION

lind user

13.. 2

Read subsystem relabeling

13-3

Convert name to user number
Convert user number to name
Wait for any fork to terminate
Read all fork statuses
Terminate all forks
Dismiss
Read device and unit
Return trom exec BRS (exec only)
Turn off teletype station
(exec only)

13-2
13-2
3-3
3-3
3-3
5-1
9-5
6-2
7-4

98
KBl~~

EXCNUN
EXCtmN
FKWA
FKRA

FK'm
IMS

RDU
BRSRET

TSOFF

MTDI
CKDOPN
RURL
SURL
mET
TREL
APM'l'E
DH4TE

MPAN
RTUN
RDRM
WDRM

DGET

DOL

---.

99
100
101
102
103

104
105
106
107
108
109
110
111
112
113
114
ll,5

116
117
118
119
120
121
122
123

l24
. 125
126
lZf
128

Disconnect W-butfer (exec only) 9-6
Skip if no drum files open
Read user relabeling
'-3
Set user relabeling
5-3
Reserve tape unit (exec only)
9-6
Release tape unit (exec only)
9-6
Assign EMf entry (exec only)
'-3
Release specified FMT entry
'-3
Simulate memory panic (exec only)6-2
Read teletype and user number
13-2
Read 2K block
10-3
Write 2K block
10-3
Allign 2K page
10-3
Release 2K page
10-3

A-5

()

NAME

RDBA
PTR
PTW

SKUEX

WIR
NTOS
MFLSH

RSCP
SSCP
RDSS
STST

NUMBER

129
130
131
,
132
133
134
135
136
137
138
139
140
141
142
143
111-4

FUNCTION
Read drum assignment
Position tape to read file
Position tape to write file
(exec only)

12-17
12-17

Skip if caller executive

Wait for input request
Suppress or allow output
Force drum/core correspondence
Read status of caller
Set status of caller
Read status
Set status

7-5
7-7
5-5
6-2
6-2
9-1
9-1

B-1

C~)

SYSTEM PROGRAMMED OPERATORS
BIO
TCO
TCI
BRS
CTRL
SBRR
SBRM
STP
LDP
Gel
WCH
SKSE
SKSG
CIO
WIO
WCI
FAD
FSB
FMP

FDV

EXS
¢ST
IST
SAS
LAS

DW¢
DWI
DBO
DBI
ISC
(-i
~"---_/

SIC

176
175
174
173
172
171
170
167
166
1&.5
164
163
162
161
160
157
156
155
154
153
152
151
150
147
146
145
144
143
142
141
140

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-outp~t
Write character and increment
Floating add
Floating subtract
Floating multiply
Floa.ting 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 irlternal conversion
(floating input)

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
l!5-2
15-2
6-2
7-4
7-4
10-3
10-3
10-1
10-1
10-2
10-2
l!5-4
15-4

II:
Ii
:1
II

II
II

il
II

B-2
/'---."

STO

137
136
135
134

BPT

135

GCD

STI

weD

Get character and decrement
Simulate teletype input
Write character and decrement
Steal teletype output
Breakpoint (BRS 10)

14-2
7-7
14-2
7-7

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