ERA 1101 f11 Storage System

•

"

621.31'.'72 :

621.385.132

:

5.'.5

(1) IN'I1lODUCDON

Propoeak for the

coaitructioo

of

~

diaital

computiq

macbiMI

haw

nsu1ted

ill

a

~

'for •

DOW

type

bl

atorqe

system.

'In

order to, eltabJilb a

~

aaainst

wbidl

the

particular

stora_

syttem

dclcribediD

the

p&.ent

paper

may

be

let,

the

introductory

SectiGo

of

die

.....

,-=--

a

delcriptioo

of

the

ayMem,

oIllumbara

to

..

..ct

•

propoeed

computina

machiDea,

tbe·,~

.......-

C"6

....

aystem.

and a

statlme.tlt

of"

...

dpea~:I!IMI~

."

.........

'.,...'

"

."

'1:'.'

.',

,

.',

(1.1)'

'III!t.

.....,

',""

.,

PI

••

,

..

Tbe~'ol

....

tIiIiIal~""the.,mecr

iDa

ItaDdpoinf,

~priinariIJ.

ia

the

~

of

8uitable

. electronic

devices

.haviaa

tho

lime'

IlUIftber

()t·lta.

as.

the.'

lif)atimber

or

P<*l~

values

.r

a

dilit.

10

that

• oao-to-oDe com- .

~

spoo.deoQC

may

be

~blished

between

each

s_

of

the device

,

aDd

eadl value

or

die

diait.

The'

number

of

values which a

digit may

take

depends,

of

COUlICt

Gl

the

system

of

numbers

tiled in

the

machine,

and

it·

follows

that

it is advantageous

to

dIooIe a

system

wbic:bcan.be~Dted,

elcc;trically . with

ease

and

e(:ODomy.

For

theIe

reasons

the

binary ,system

of

numbers

bas

~

popular

in

reoeat

plans fqr.

~Jectronic

digital

com-

putina mach ina.

I,

1 although in the past the

decimal

system has

bOea

\IIed.J.4«

' ,

Systems

of

numbers may be derived

from

the

common

series:

a._.IJra-1 +

...

,+

....

+ a,bl +

tJobO

which repreaents all intelen with "

siaamcant'

figures.

The

dccinial systaD,

(or

example, is obtained

jf

b = 10,

and

-the

a's

are allowed

any

one

of

the

vaI~

,between,

,and including, 0

and 9.

In

tbebinarysyst.elJl b

==

2

and"

is.either 0

or

l.

The

decimal number

19.

say,

is

d1cn1 X

24

+

0'

x -2l + 0 x

2l

+ 1

X

21

+ 1 x

20

~

the

binary

scale, which

can

,be writtc

..

10011

with

the

least

sianificant

figure placed

on

the.

right.

The

decimal,

or

binary, POint is

OD

the immediate right

of

the

term

tJobO.

The series can

be

CQIltinued

to

the

right as follows:

Prof. WiWama &ad Mr. KJlbUl'll

are

at

the

UaiversitJ

ot

Mancbestcr.

"'"'

-~I'.

-10

.........

.'

..

. 1

•.

/1

.

::1.

..• ,.-

;~3"

-0

~

'~

-.;

o

..

(h)

'C

FII~

l;~;~.~llCli~.

(a)

SedeI:

~

.....

p ,

;~9i;~:"

ebaaDeI

•.

(.)PuaIId:

pu1Ie

00'

...

·......'

"

, equivalea.t

of

the

Dumber

19' being

used

as

All

example.

In

tbC

Figure. video pulses are'uaed for. digital repreIeIltah9n.

and

at

Fig. j (a) . the least

signifiant

figure,

is

plaQed

on

the left,

so

that

time

can

be

shown increasing from left

to

right

in

the

conventiOnal:

JDaJU1CI'.

.

Information may be represented

~'dynamicallyU

by

pulses~:

,i

which'

only exist transiently,

or

"statically'· by

d,c.

~~-,

'-

flip-flop circuits. which retain the information until

tbeyale

"~

(

81

1 . t

. ! . r

'.

T\.~$~'l\)£.R,

.

,;;

. .

'.

U,~\..~,

.........'..

~d:f.i

~~~~

__

"~~_'_'_w~L'_\:'_)~'f'_'~~&~"~-_M

__

~N~t~t~·~~~\~~(~~t~~···.~it~;_H·~)j~~~'~**·~t*~b~~j~·C

___

~'~*,

__

*

__

~'~~-~;m~;·~+wt~·~~'**.·:_'~·*~HM.L~·~~~$~"~~~¥~:'5~~~~~;b~~~'4~~;~~~~'<~*~';~~.h¥~;·~~·~*.·(~q;~@t~~1

• •

-.

\

82 WILLIAMS AND KILBURN: A STORAGE SYSTEM

FOR

purposely reset

to

a

standard

condition.

Dynamic

information

may be converted into static information by, for example,

applying the pulses shown

at

(b)

to

five d.c. coupled. flip-flop

,"

circuits.

The

set

of

flip-flop circuits is called a

"staticisor."

( 1 .

3)

Required Properties

of

a Storage System

It

should

be

stated

at

once

that

a

computing

machine

cannot

·'think."

It

follows

that

the first step in setting

up

a problem

on

a machine

is

to

sub-divide it

into

a sequence

of

simple

arithmetic

or

logical operations externally (i.e. outside the

machine),

and

construct a

~

"table

of

instructions." Each

instruction in the table will, in general, require

that

an

elementary

operation be performed

on,

or

by, a number, i.e. a

number

will

be moved from one

"address"

of

the machine

to

another.

To

'every address a digit combination will be assigned

•.

so

that

an

instruction consists

of

two digit combinations, aRd is indis-

tinguishable from a

number

in appearance. Instructions

and

numbers, which

are

collectively termed

"words."

are

therefore

similar, the only difference between them being their function

in the machine.

Since all the words applicable

to

a

probl~m

cannot

be intro-

duced into the machine simultaneously, they must be

'~remem

bered" during the loading period,

and.

until used, during the

solution. Further, temporary

"memory"

of

some type must be

provided during each elementary

computing

operation.

The

storage system provides this memory property

of

the machine.

The

general opinion

of

mathematicians is

that

it will be

necessary

to

store approximately 3·2 X 105 binary digits,

in

the

form

of

lC4

words, with 32 digits

per

word.

If

the two-valve flip-flop circuit. were used,

6'

4 x

lOs

ther-

mionic valves would be required, which is clearly' impracticable

from the

points

of

view

of

size. cost

and

probable

reliability

of

the

equipment. Even in smaller machines the use

of

flip-flop circuits

would defeat,

to

sOme extent. the purpose

of

the change from

decimal

to

binary representation, since decimal representation

by ring counters in a machine

of

similar capacity would require

only three times

more

valves;

and

against this would have

to

be

set the expense

of

the conversion from the decimal

to

the binary

system,

and

vice versa when a binary machine is used.

Recently developed two-state devices, which

are

far less com-

plex

than

existing two-

or

ten-state devices. are the main justifica-

tion for the change

from

decimal

to

binary representation.

Further, they make digital computing machines with large

storage capacity a practical proposition.

Sufficient attention has been given

to

the memory property

to

indicate

that

it is

of

primary importance,

but

in

order

to

make

practical use

of

a store it must also

be

possible

to

insert, extract

or

erase the remembered information.

The

insertion

of

informa-

tion into a store has been

~alled

··writing.·'

The

extraction

of

information from a store.

"reading."

does

not

imply

that

the

information

is

erased from a store, since it may be required

at

a

latcr time.

"Erasing,"

of

I:ourse, implies

that

informati,on is

era~d

from a store.

but

in its prefcrahle form it

is

really a super-

sedtng process in

that

a word may be written into

an

occupied

address. deleting the word already there. This property increases

the etfective

capa~lty

of

a storc. since new inlormation, such as

panial

answers. may he '\\rincn ovcr information which has been

used,

"ithout

an

intermedlah! crasurc

proccs~.

T

\)

summarilc. a st(lrc

mu"';{

ha\c

the following propert:es:

(a)

It

mll

...

t

tx:

pOSSible

tll \\ rile a

\hlrd

qtl1\:kly into any

addrc!\s,

~Lh;h

\\

riling superseding any word alread) present

at

that address.

(/I)

1 he

\\tll\.!s

at all

adJrc"~,,,

not hcing \\filten in must

he

rcmemhcreJ inddinitcly, ch.tnges occurring only as the result

()f

a detinite writmg prcx:ess: errors

of

I digit per million would be

fatal.

,

(c)

11

must'be

possible

to

read the word in any address quickly

without erasing it,

or

.any

other

word.

(d)

It

must be possible to write into

or

read from any address

with absolute certainty. Reading from

or

writing into

an

adjacent address in

error,

even

if

it occurred only once in a

million times, would be a serious disadvantage,

(e)

The

sfore must

be

capable

of

holding a very large number

of

words

(about

1(4)

each comprising a number

of

digits. which

are

either

O's

or

I's.

For

(0)

and

(c) the significance

of

"quickly"

is

the

time-scale

upon

which the machine as a whole is

to

work. The

longest operation

of

frequent occurrence

is

multiplication.

If

this process occupies, say, 5 millisec

wr~ting

and

reading should

occupy less than, say. 1 millisec, otherwise the computation will

be seriously retarded.

The

paper

describes

an

attempt

to

meet these requirement,

using charge storage

on

a cathode-ray-tube (c.r.t.) screen as the

memory mechanism.

./

(2) PHYSICAL BASIS

OF

THE

STORAGE SYSTEM

Before describing the mechanism

of

digit storage, the arrange-

ment

of

digits

on

the storage surface will first be mentioned

The

digits

are

reprtsented 'by charge distributions which

exi~l

o~

small areas

of

a c.r.t. screen. the charge distributions

bein~

arranged in

the

form

of

a two-dimensional array. This array IS

produced

by a television type

of

raster, in which the digits

of

a line.

and

the lines

of

the raster,

are

scanned sequentially, each

digit corresponding with a

"picture

element.

to

Typical displays

are

shown in Fig. 2, which illustrates the appearance

of

the C,T.t.

(a)

(h)

(,I)

I

"~I

,1

..

':01'

If"

:

0":.""

dl~IL'"

'k'·

face

\\hen

'itm'age is

in

rlllgrl.':-....

In

Fig.

21n) there

an!

J2

lir.

c~lch

of,12

digits,

ILKh

dIgit

Il1LlY

have one

of

two t,,'rnt--

indicatcd

hythe

r;lttcrn

Slll'\\1l

)toreJ.

A

"signal"

or

"pick-t:

plate,

nlOsi~tm~

of.t

~hl.'('{

llf

In.:t;!1 toil, fir gau7e,

e\ternal

h.)

t:

c.r. tube is

d~)sdv

attached

III

the

t'a~:c

of

the

tube

isl.'l.' Fig.

Fach

arca

of

thl.'

...

aCt-'1l

I"

therefor\.'

Capa(ltance

courkd

mt('

i.-/3

•

PICk

-

up

plate

1-----0

Output

'--

__

...J

IJ

100

MO.

The

voltase

output

from

the

amplifier

is.

then.

I

volt

per

hundredth

of

a microamp

of

current ftowina

to:

or

from,

the

pick-up plate.

There

is

no

plwe

reversal

in

the

~fier,

and

conventional current ftowing" from the pick-up plate

to

tbe

amplifier

sives

a positiVe

output

voltap.

It

should be noted that this equipment can only detect rates

of

C'hanp

of

surface chariC

on

the c.r.t. screen, so

that

thefoUowiaa

daaiptions

of

potential distribution

on

the screen are

qualitati~

The

absolute value

of

these

distributions is

not

of

primary

. importaDcc to the final

~toraae

system.

FII.

3.-DetJtion

or

lianaJa.

(2.2) Pot6iIdaI I>JIbiIJutbI

db

Steady

SiIIIIe

Spot

common duumel,

as

in the iconoscope. This

method

of

detect- In a c.r. tube which

has

its deftector plates; internal con-

ina

changes

of

charge

on

an

insulatina surface has also been

UIed

ductive

coatiq,

and

first

and

third anodes all connected

to

earth

to

determine

the

ICCOIJdary

emission ratio

of

insulaton usina potential.

and

its grid, cathode

and

focus

electrodes

connected

pulse technique.' .

in

a normal

manner

with respect

to

a

neptiyc

poteDtial (say

Havin. formed a general picture

of

the

rep...,.tation

of

digits - 2 000 volts), the inner surface

of

the

ICReD

will

also

be

a'

by a two-dimensional

array

of

suitably cbarlCd

aras,

attention

earth

potential, because it is in contact

by

Ieaka,e resistance

witb~

wiD

now

be confined

to

the

small area

of

the screen

correspondinl

the internal conductive coating.

~ia

~~

&bat

no

beam

with a

sinJle

digit.

The

potential distributions existin.

on

thia current

has

been preSent for some

tlrne.·~

In

the

typea

of

area

with different types

of

electron bomhaJ"dlnent.

and

the

co~

c.r. tube

invcsti~~

(CV~097

and

CVl13I).~

resuitin.

video

sipals

that

ate

obtained from

the

-'p~filf'plaelt-'

relation between

secondary

cmtsslon ratio

of

the tcrecn material

are

dac:ribed below.

Referma:s

to

literatuJ'e6. 7

on

the

subject

and

primary electron velocfty is

of

the form shown in

Fil·

S.·

of

charp

·storage have been .included.

(2.1)

FAaafpalcat

'J'be

voltap

level

of

the

video sisnaIs is increased by

connectina

the

pick-up plate

to

the

input

of

a suitable amplifier 9

as

shown

in

Fia. 3.

The

equivalent input circuit

of

the amplifier is shown

in

Fia.

4(41)

where

I.

represents

the

sianal current

due

to

electrons

To

am

!sfler

c r

(0)

To

am"ltf

..

'r

r

Fla.

4.-Amplifier

input circuit.

ur~

. €

I>nmary

eltctr~n

Wloclty

'tc.

5.-5econdary cmlMion ratio as a function

of

primary eIeruoa

velocity.

At

points

of

operation such

as

A,

the

secondary emission nahO

80

is arcater

than

unity. This is

true

for

all primary

~tia

in

the

ranae

1 000 volts

to

3 000 volts

at

least.

It

follows that if.

opcratina

under such conditions. the electron beam is switdlod

on

and

falls steadily

on

a single

spot

on

the

c.r. t.

acreaj,the

number

of

secondary electrons lcavilll the

spot

and

movina

towards

the

electrode

~mbly,

will exceed the number

of

primary

electrons arriving

at

the spot. The resultina net loss

ofneptivo

charlC causes

the

potential

of

the bombarded spot

to

become

positive,

and

its potential IS then higher than that

of

any electrode

in the tube.

Later

secondary electrons will therefore

be

ejected

into a .retarding electric field.

and

those which have emissioD

velocities below

that

CQrrespondinl with the potential

of

the spoJ

will be returned

to

the screen. The electrons with low emisSioIi'

velocities will, in fact, return

to

the

spot;

those with hisher'

velocities, repelled by

other

electrons, will have time

to

acquire

an

additional component

of

velocity parallel

to

the screen surface

arrivilll

at

and

leaving

the

screen surface;

C,.

the

capacitance

of

and

wiD

return

to

the immediate vicinity

of

the spot. Expcri-

the bombarded

area

of

the screen

to

the pick-up plate; C, the ments indicate that. for times

of

bombardment

le5S

than 400

p.sec.

capacitance

of

the bombarded area

oth~r

than

that

to

the pick-up the screen is substantially unaffected

at

distances greater

than

a

plate,

C,t the remaining stray capacitances

to

earth;

'.

the

input.

spot diameter from the centre

of

the spot.

If

tbe effective

resistance

of

the

amplifier;

and

R, the ohmic resistance due

to

secondary current

is

defined as

that

caused by secondary electrons

the fact

tbat

the screen material

is

not

a perfect insulator.

The

which leave the spot,

and

are

not

returned

to

it

by

the retarding

leakage time constant

(e

p +

C)R

is known

to

be

of

the

order

of

field, the effect

of

the retarding field will be

to

reduce the effective

O·

2 sec, while very approximate values

for

(C

L +

C)

and

R are secondary emission ratio

S.

The potential

of

the spot will, in

0·002

p.p.F

and

lOS

megohms respectively.

The

time constant fact, rise

to

a value

Eo.

thought

to

be

about

three volts.6 such

C,r is less than

0·1

p.sec

and

r

is

approximately 1 000 ohms.

that

the retarding field causes the effective secondary emission

Since R > '. the signal voltage developed

across,

issobstantially ratio

to

be unity.

Eo

can

be

interpreted in terms

l")f

the '¥clocity

unaffected by R, which

is

therefore neglected.

The

pick-up plate distribution

of

the secondary electrons.9 typically.

indi~ated

in

current appropriate

to

i,

and

,flow'ing

through ep is very nearly Fig. 6 as

that

point

to

the right

of

which the number

of

sec,}nJ.lry

C,;J(C

-t

Cp

'.

so that thetinJ"ut circuit may

be

reduced

to·that

electrons per unit time equals the primary current

Ip.

The

shown

in

Fig. 4(h). the final signal voltage being C"r;J(C

+'C

p

)'

potential

of

the

spot

will

now remain constant at

Eo.

but the

The amplifier. which

is

fuUy

described

in

Appendix

9.1

bas

a longer the spot

is

bombardeJ

the larger IS the affected .lrl!a around

bandWidth

of

2 Mc/s, and may

be

regarded as a resistance

of

it. The potential distnbution

on

the screen

is

~ummJrizcJ

10

'';'

£.

-13

•

• '

•

• j

Pnmary

wloClty

....

6.-Velocity distribution of

secondary

electroua.

Fig. 7 in which increasing positive potential . is plotted in

the

direction

of

the

arrow,

so

that,

us~

the analogy

of

gravitational .

fie~d.

electrons may be said to

'~faW

towards regions

of

positive

o

+1

-~~~-~-ov

U~

-

--Eo

....

'I.-Potential

distribution with a

sinale

spot-a

"well."

potential. The depression in

the

distribution has been

termed

a "well."

TIiC

time taken

to

elItablish the potential

Eo

depends

on

the

, capacitance per unit area

of

the

screeD,

the

current density

of

the

beam, the secondary emission ratio

and

the

velocity

distributiOn

of

the

aecondao'

electrons.

It

follows that, with a

given

c.r. tube,

the time taken is inversely proportional

to

the current density.

Defocusing

at

constant beanJ..cunent,

to

double the spot dia·

meter,

will

increase the

time

scale by four, whilst doubling the

beam

current, with constant spot size

wiD

hal\'C

the

time scale .

1be spot capacitance

appean

to

be

charged exponentially towards

Eo

as shown in Fig. 8(a), and the electron

beam

may be regarded

Fla.

I.-Owaina

of

a bombfrded spot

to

equilibrium potential.

as

an

ohmic resistance to the first order

of

approximation, the

time constant formed by the spot capacitance and beam resistance

being

of

the

order

of

I

p.sec

or

less.

The net

current;

flowing

to the spot

is

therefore

of

the form shown in Fig. 8(b), rising to

an initial value

Ip(So

-

I)

corresponding with the secondary

emission ratio

So,

and falling approximately in

an

exponential

manner to zero as the effective secondary emission ratio,

8,

approaches unity. The area under the curve is the charge

required

to

raise the spot capacitance through

Eo

volts, and

is

therefore proportional

to

spot area. Since the capacitance

of

the spot

is

almost entirely that to the pick-up plate,

this

current;

wilt

also

flow

from

the

pick-up plate to supply

the

required bound

negative charge. The

pid-up

plate meaSures the rate

of

change

of

charge over the whole screen surface, and this means that the

electrons which return to the screen around the spot will cause a

slight reduction

in

the plate current. A. further reduction. due

to another effect,

will

now

be

described.

,

(2.3)

Effect

or

lDtaiiaptina the

Beam

OD • SiIIIIe Spot

With 'the spot held stationary as before, let

the

beam current

be switched on and off by applying a square waveform

of

fre

..

.

Quency

I kc/s to

~control

grid

of

the c.r. tube. When

the

beam

is

switched on for the first time, the potential distribution

shown in Fig. 7 will be established on the screen surface; but, sub..

sequentlyat instants

of

switching on the beam, substantially

no

change will

ha\'C

occurred in this distribution,

bccaU!e

the

leakage tiJne..constant

of

the

screen

(C,

+ C)R is large compared

with a cycle

of

the grid modulating waveform. It follows that

only a small change

in

surface charge is required

at

theae instants

to

maintain the potential distribution, and conJequently the

output voltage

of

the amplifier in Fig.

3.'

due to this

dlanae.

is

negligible. Howe\'Cl', when

the

beam is switched on, • cloud

of

electrons

in

the

secondary current, and in

the

beam

itself:

is

suddenly introduced in

the

vicinity

of

the

pick-up plate.

Thil

is

equivalent

to

bringing a negative charae near to

the

pick-up

plate,

and

a transient current flows

to

the

pla~

to

supply

the

required induced positive charge. 1be electron cloud is intro-

duced extremely rapidly

if

the grid modulating square

waw

It

sharp, and

the

shape and time

scale

of

the resulting amplifier

output pulle, whidl is negati\'C going, will be

defined

entirety by

the

transient

response

of

the amplifier.

When

the

beam i •

switclled

otT

by the'square wave, the

electr~n

cloud is suddenl)

removed and

an

equal

and opposite positive pulse appears at the

F'II.

9.-Electron

cloud

pUlses.

(G)

Grid

modlliatina

waveform.

(11)

Amplifier

output

.

amplifier output, as shown in Fig. 9. The amplitude

of

these

pulses increases with

the

beam current. TIle pulse waveforms

are completely independent

of

spot

size.

(2.4)

Interrupted

Doable

Spot

Two spots,

as

shown

at

1

and

2 in Fig. JO(p), may be obtained

on

~

tube screen by applying

to

a deftector plate' a square

CntKAII~

~

Rt6

~11JiuL

!

I~'I""'·

j I

I'

~

(C)

q

MID

1

,-,

~'

...

~.~

'1.+

tAv

Fig.

to.-Interrupted

double-spOt

potential distributions.

waveform having half the frequency

of

the grid modulating

waveform, and phased relative to it as shown in Figs. J 1(0) and

11

(b).

If

the spot

is

initially at

I,

the potential distribution will be as

previously described and

is

shown

by

the full line in Fig.

JO(b).

The beam is now

~witched

off, and then switched on again

in

position

2,

causing this spot to move rapidly positive and

generating the

well

shown dotted .

If

the separation between the spot centres

is

greater than a

critical value (about

l'

33

spot diameters), no other effect

will

•

4-

/3

•

USB

WI1H

BlNAltY-DlGlTAL

COMPUfING

MAOIINBS

.5

_

--f~}-~--r

1--

f-l_.~

c:

'-'

: '

'_I

, :

rRlsiticn

I

W-P",

..

:--u...

'J!

:4-'...J~2

'('lR1

: i I I • I

. I I I

, I I ,

Ie)

, , I ,

I.

f'

I • t

tIJ

I • I

I',

f

~

• I • r I ,

(i'J~J-L-~~~

Y' I , i

~

: , I

I : I I : : ' I •

. -

~.x;

l :

~

:

~

<f)

Pig.

I

I.-Interrupted

double-spot wavefonns.

(a)

Grid

modulatiq

waveform.

(~

Shift

waveform.'

(c

Output

pulse

due

to

i

•.

(d

Output

pulse

due

to

ir•

(~

Outl"UI pulse

due

to

i~.

( ) Amplifier

output

voltale.

oocur, and

at

subsequent instants when the beam is switched on

in the positions

1,2,

1

and

so on. this double well distribution will

be maintained by insignificant changes in surface charge, making

aood

the small leakage, as. was the single well distribution

described

in

the previous Section. ConseqUently the amplifier

output

waveform will again

be

as shown in Fig. 9(h).

If, however, the separation is less than the critical value,

as

shown

in

Fig;

100e),

some

of

the

secondary electrons emitted

during the excavation

of

well 2 'will

be

attracted

to

well 1

and

begin

to

"refnr'

it

as

at

Fig. 10(d).

1be

extent

to

which well 1

is

refilled depends

on

the separation between the spots.

and

the

time for which

weD

2 is bombarded,

but

it

is probabiy never

completely refilled with the times

of

bombardment

used

in

practice, since'

the

fuller

it

gets

~be

less likely

are

secondaries

from

well

2

to

reach it. The

panell

refilling

of

well 1 causes a

potential distribution in position 1 corresponding

to

an

effective

secondary emission ratio which is greater than unity, since

for

unity ratio a well must

be

excavated

to

the depth

Eo.

Therefore

when the beam is switched off, moved back

to

position I.

and

switched

on

again, well I

is

rapidly re-excavated

to

full depth,

whilst well 2 is panially refilled, producing the distribution shown

at

Fig.

100e).

This process

of

excavating one well

and

panially

filling the other can

be

repeated indefinitely. and.

if

the system

is

symmetrical. the charge ejected from one well will equal in

magnitude

that

deposited in the other. since the charge ejected

was deposited during the previous half-cycle

of

operation. In

fact,

if

the precise electrons emitted in excavating one well went

immediately

to

the refilling

of

the other, no signal due

to

changes

in

surface charge would

be

obtained. However, the excavation

process is much more rapid than the refilling process, as would

be

expected from

t~

fact

that

whereas all' emitted secondaries

emerge with velocities away from the well being excavated, less

than

half

or

them have a component

of

velocity in the direction

9f

the well being refilled,

and

many

of

these have velocities

too

great

to

be attracted

to

the well,

or

to

any part

of

the screen.

The amplifier

output

pulse~

at

the instant

of

switching

on

the

beam, under

th~

conditions will therefore be the sum

of

three

pulses. namely

that

due

to

excavating a partially filled well

to

full depth. that due

to

partially filling the adjacent well,

and

the

negative pulse induced by the introduction

of

the electron cloud.

These effects will

be

considered separately.

The excavation

of

a panially tilled well

to

full depth establishes

an

additional positive charge

on

the screen surface, which binds

an

equal and(oPposite negative charge

on

the pick-Up plate.

This negative charge is produced by a current

i.flowing

from

the pick-up plate into the amplifier input circuit,

and

a positive

pulse is obtained

at

the amplifier output.

The

current

i~

is simflar

to

the current ;

of

Section 2.2,

but

its initial value corresponds

to

an

effective secondary emisSion ratio

less

than

80,

since the

excavated well was only

pa~ially

filled.

Thil

current is

abo

, slightly modified

by

electrons

retuminl

to

the

'ICfeCfl

around

the

well. With a perfect amplifier the

output

pulse, which is

indicated

at

Fig.

11

(e), would be a replica

of

i •.

The

partial refilling

of

the adjacent well reduces

the

positive

~surface

charge in

that

position.

and

releases

an

equal

and

opposite

bound

charge from the pick-up plate. Heoce a current

i,

ftows

to

the pick-up plate

and

a negative pulse

is

obtained

at

the

output

of

the

amplifier.

The

areas

under

the

i.

and

i, wavefonns are

equal, because the charges involved are equal. but i, has a lonaer

time scale

and

a smaller amplitude.

1be

I, waveform is shown

in Fig. J 1

(d),

and its shape

chanaes

with

beam

cu.rrent

and

spot

size in the same manner as ;

or

i,

(see Section 2.2).

The induced current

ie

which ftows because

of

the presence

of

the electron cloud has been described previously,

and

produces

the

output

waveform shown again

at

Fig. I I (e).

The

net

output

voltage

of

the amplifier is the sum

of

the three

waveforms (e),

(d)

and (e), Fig. 1

I;

and

is

typically as shown

at

(f),

though many variations are possible by adjusting brilliance

and

focus.

The

net pulse

at

the instant

of

switchina

on

the beam

. can, in fact,

be,

made negative

if

the brilliance

is

sufficiently

increased,

but

it is

not

proposed

to

run

the C.T. tube in this

condition.

(2.

S)

Separadoa.

or

DCMlbJe-Spot

It

follows from the previous section,

that

both

the amplitude

and

sign

of

the pulse obtained when the beam is switchesl on.

with fixed beam current

and

focus, depend

upon

the separation

of

the spots. This pulse

is

that marked X in Fig.

11

(1),

and

its

amplitude change as a function

of

the separation between

spot

centres is summarized in Fig.

12.

The pulse shown

in

Fig.

1..1(.)

j

~!l

~~

~

llP'---:=---~-

fa~

~~40

2

~~~d~rlrr.-d~~~

Separation

,In

spct

diameters

Fig.

12.-Output

pulse at beam switch-on as a function

of

double-spot

separation.

occurs

about

O'

2

(Lsec

before those shown

at

(e) and

(d).

because

the current pulse in the pick.-up plate. which produces the

.'

output

waveform (e), is much larger

and

narrower than the

current pulses which produce waveforms (e)

and

(d),

and the

output

of

the amplifier therefore responds

to

it with less delay

time. Hence, the pulse X

is

never quite zero

at

a'ny

value

of

spot separation, but may

be

a small negative pulse followed by

a small positive pulse.

For

this reason the positive and negative

amplitudes are plotted separately. In plotting Fig.

II

oldy the

amplitude

of

the pulses immediately following the instant

of

beam switch-on is considered. The negative overshoot

of

the

pulse X due

to

partially retllling the adjacent well

is

ignored. as

is the positive pulse contributed

by

waveform (e) when the beam

. is switched off.

Referring

to

Fig.

12.

if

the separation

is

7.ero,

the conditions

are identical with those for a single spot and the pulse

is

negative,

as shown in Fig. ]

3(a). The pulses in the latter

fi~ure

are tracings

taken during the experiment from the face

of

a tuhe monitoring

the amplifier output. As the separation

is

gradually incrc:l,ed.

the negative pulse decrcases in amplitude :lnd

is

31most zero with

a separation between centres

oro·

flYd. d being the diameter

of

the

spot. During this time. the

po..;itive

p.plsc

amplitude

is

increasing,

the waveform being as inJic.lted in Fig. I J(h). The positive

L.-/3

•

'.

WILLIAMS AND

XD...BtJRN:

A STORAGE SYSTEM

FOR

(0)

6 , 4

~

8

!I

lIme.f'S

i<:3

:~b

8

~

(b)

TIme.

#AS

~

f'l

'

!f

(c)

20

O}46A~

Ttmt.J.IS

FII.

13.-Output

pulac

at

beam

switch-on.

(Cll

Separation

-zero

or

peater

&baD

1 .

3Jd

(critical).

(6

Separation

-

O·l5tl.

(c SeparatioD -d

to

1 .

If

•.

. puJIe continues

to

increase

Up

to

a separation

d,

i.e.

no

overlap

betvtwD

the

spots,

and

then

passes through a flat maximum

between

d

and

l'

J6d.

The

pulse during this stage is shown

in

Fia.

13(e).

The

amplitude

of

the

positive pulse falls oft' quite

lharply

towards

zero

with

increased

separation beyond this

point, while

the

negative pulse amplitude increases

rapi~ly

from

ao

until

at

l'

33d

the

output

pulse is entirely. negative

apin

as

at

Fig. 13(a).

Separations

greater

than

l'

33d, which

has

been

called critical, give

no

further change. .

. Six curves

of

which Fig.

12

is typical, were taken

for

various

fiMd

values'

of

beam

current

and

focus.

The

negative pulse,

the

amplitude

of

which gives a measure

of

beam

current,

was

varied

in

amplitude from

16

volts

to

42 volts;

and

the

spot

diameter was varied from 1 mm

to

2t

mm.

For

all the curves,

the

aitical

separation

was

within

the

limits

l'

28d

to

1 .

3&1.

with

the

mean

value

I·

33d.

The

diameter

of

the

spot

was

deduced

from the

amount

of

shift required

to

move

the

spots from

coincidence

to

just

touching.

The

difficulty

of

setting

up

the

latter condition visually may involve errors

up

to

about

± S

%.

The

critical distance has, then,

no

a~lute

value. In the

case

of

two spots

of

equal area,

it

is equal

to

kd,

where k =

1'33

for

the

particular

SCMen

ma~rial

investigated. (The separation

experiment was performed with a CVI097

type

of

tUbe.)

The

fact

that

the

critical distance increases linearly with

spot

diameter,

indicates, as might

be

expected,

that

increasing linear dimensions

has

no

effect.

For

the

increased separation is compensated by

the 'increased attraction

on

secondary electrons

by

the

adjacent

well, due

to

the increased

spot

area. .

The

constant k is determined by

the

screen material,

and

will

depend

on

the velocity distribution

of

the secondary electrons,

for

this determines

the

depth

Eo

of

a well,

and

therefore influences

the

attractive force

due

to

the adjacent well.

The

secondary

emission ratio, like

the

beam

current, influences only

the

times

taken

to

excavate

one

well

and

fill

the

adjacent'w~ll.·

(3)

APPUCATION

TO

DIGIT STORAGE

From

the phenomena described above, the following

state~nts

may

be-

made:

(a) Either

of

two states

of

charge may be left

at

will

at

a given

spot

on the c.r.t. face. These states are

(i)

a

well

of

full depth, by bombarding the storage spot, ceasing

the bombardment

and

not

bombarding any

other

spot

in

the vicinity,

or

(ii)

a partially filled well, by bombarding first a storage spot.

and

then

another

spot

in

the vicinity before ceasing

bombardment.

\

(b) Charge distributions will be maintained for a

timo-a

few

tenths

of

a

second-depending

on.

surface leakage.

(c) Renewed bombardment [within the few tenths

of

a second

,noted

under (b))

of

the storage

spot

will give,

at

the instant

of

recommencing bombardment, a negative signal from the amplifier

in

case (a) (i),

or

a positive signal in

Case

(a) (U).

(d)

Bombardment

of

spots displaced by more than 1,

33

spot

diameters from a given spot has

no

influence

on

the potential

distribution

at

that

spot.

Item (a) above indicate! a mechanism

of

writing a digit

on

a

storage spot,

and

item

(c)

a mechanism

of

reading it. From

(b)

it

is clear

that

the

~rent

storage time is inadequate. This can' be

overcome

by

ananging

that

each stored digit

is

read

and

~

written well within the inherent storage time, thus giving a

new

.

start

to

the stored charge with all the leakage compensated. This

. "reaeneration" process completely eliminates the commonly

quoted objection

to

digit storage by charge distribution, thaI

leakaae will lead

to

"spreading"

and

mutual interference betweaI

digits,

it

also has

other

advantages described later. .

Item

(d)

is

important

in

that

it

sets a limit

to

the

cl~ness

With

which

individual storage spots

can

be packed

on

the

stOlql

surface

and

hence influences the digit holding capacity

of

the

store; this factor is discussed next.

(~1)

Estimated Separation and

Ammgemeot

of

Storage

~

Since

each storage

unit

of

the type outlined requires a c.r. tube,

amplifier

and

regenerating Ihcchanism,

it

is important

ec0-

nomically

to

store as many digits as possible

in

each unit.

It

bas

been shown

that

bombardment

of

the

screen

at

a distaooe

or

more

than

1· 33d from a storage

spot

has

no

influence

on

that

spot.

It

follows

that

the

single storage

spot

considered so rar

can

be surrounded by

other

storage spots, provided

that

the

separation

t.etween

spot

centres is greater than 1· 33d.

For

I

present purposes a separation

of

2d will

be

assumed (ace So.;. i

tion

5-.3).

Furthermore, each storage

spot

must also have

reserved

an

adjacent

spot

which

can

be bombarded

to

perform

the

"filling" process.

1be

form

and

magnitude

of

this additional

area

depends

on

the

detailed arrangement

of

the system,

but

in

•

simple

case

it may

be

considered as a second spot spaced d from

the

storage

spot.

The whole storage element is then contained

in a rectangle d x 2d. Associated with each such element is a

"separation area"

to

provide clearance from

other

element'

The

boundary

of

this separation area must, for safety, be

at

least

!d

away from the boundary

of

the storage element proper.

The

whole rectangle occupied by each digit is therefore

2d

x

3d

and

it follows

that

an

estimated area

of

6(/2

is required per digit.

or

0'06

cm

2

if

d = I nun.

The

screen

of

a c.r. tube is circular

and

a circular array

of

digits

would give optimum use

of

the available area. This is difficult

to

arrange

and

in any case assumes complete absence

of

plate

shadow. Accordingly a rectangular array has been. chosen. A

~in

tube, which has

an

available area

of

8 cm x

12

cm, should

therefore have accommodation for I 600 digits with the estimated

allocation

of

0·06

cm2 per digit.

Greater

numbers should be-

come possible by improvement

of

focus,

or

by increase

of

tube

screen area with given focus.

Bearing in mind that each digit

is

to be regenerated

at

frequent

intervals, necessitating continuous scan

of

the whole array.

the

method

of

setting

out

the array is

to

set up the

digit~

in a series

of

spaced horizontal

lines·

as in television rasters, as mentioned

earlier [see

Fig.2(a)].

Willi this arrangement the basic requin:-

ment

is

regenerative storage

of

a number

of

digits on a

sin(EK

. horizontallir..e, the array bemg developed from the line

by

shiftillt!

the line perpendicular

to

its length through

2d

after

cadl

horizontal sweep.

L-/~

•

USE

WI1H

BlNARY-DlGlTAL

COMPUI'ING

MACHINES

17

Many

sys~

deriwd

from

the

properties stated

in

Section

3,

may be

used·

to

regenerate

the

s~

information. Five such

oriJiDal

systems have been tested,

and

although, for reasons given

later,

it

has

been

decided

that

one

of

these

is

outstaodin.

at

present, a brief outline is given

of

the alternatives, because, with

further. development, this decision will

be

reconsidered.

The

first

four

of

these

systems operate

on

the pulse obtained from

the

amplifier when

the

electron beam is switched

on

to

a spot,

and

all

use

the principle

that

the sign

of

this pulse is positive

or

negative depending on whether an adjacent

spot

within

the

critical

diStance

has

or

has

not

been bombarded

since

the storage

spot

was last bombarded.

The

fifth system operates

on

a slightly

different principle explained later.

(3.2) System

I-Dot-Dash

Display

Fig. 14(h) is a segment

of

a horizontal time-base waveform in

which short

periods

of

constant voltage alternate

with

lonser

(a)

Dot

display.

(b~

Dot waveform.

(c

Dash

display.

(d

Dub

waveform.

(d

Strobe.

(/)

Dot brilliance waveform.

(g)

Dub

brilliaDce waveform.

(It)

Time-b

...

waveform.

periods

of

constant rate

of

change.

If

a repetitive waveform

of

this kind, containing, say,

32

such segments is used

to

deflect a

c.r.t. spot, which is intensified only during the periods

of

constant

voltage, by applying wavefonn

of

Fig. 14(/)

to

the

control grid

of

the tube, then a row

of

32 dots will appear

on

the

screen.

Two

of

these are shown

at

Fig. 14(a).

If

the separation

of

thC

dots is

in

excess

of

1 . 33d, each

can

be used independently

as

a

,storage spot, the beam being

used

to

operate

on

each

one

in

turn. TIle corresponding amplifier

output

wavefonn shown

at

Fig. 14(b)

goes

negative

at

the instant

of

switching

on

the

beam,

as stated in Section

3[a(i)],

since there has been

no

bombardment

of

spots in the vicinity between successive bombardments

of

the

ltorap

spot.

If

the intensifying wavefonn is changed

to

Fig: 14(g)

the

dots

on

the

C.r.

tube will change into short lines

or

"dashes"

(see Fig. l4(c»). The initial dots are spaced by

about

3d

so

that the

dashes

may be accommodated. The amplifier

output

waveform

is

now as shown

at

Fig. 14(d). 1be

pRdae

nature

of

this wavefonn will be explained later,

and

it

is necessary

here

to

note only

that

the initial pulse when the

beam

is switched

on

is positive. This is in accordance with note

(a)(ii)

of

Scction 3.

because now there has been bombardment

of

spots in

'the

vicinity

of

the

storage

spot

since the latter was last bombarded. This

bombardment

took

place during the previous

sweep

as the

spot

moved away from position

(i)

towards position

(ii)

[Fig. l4(c)].

Dots

and

dashes thus correspond with states (a)(i) and (a)tii)

of

Section

~

respectively

and

give rise

to

characteristic signals as

defined under (c) in

that

Section. Either

dot

or

dash may be

written

in

at

will by using either wavefonn

(f)

or

(g)

of

Fia. 14

as

an

intensifying wavefonn.

On

a subsequent

sweep

dots will

be "read" as negative

output

pulses

and

dashes

as

positive output

pulses. irrelevant parts

of

the amplifier

output

waveform beiDa

discarded by using the "gating" waveform

or

strobe shown

at

Fig.

14(1").

In

order

to

make the system regenerative it is necessary

to

cause dots to be re-written wherever dots

are

read,

and

dashes

to

be re-written wherever dashes

are

read.

That

this procedure is

possible may be seen from the fact that whether a

dot

or

a dash

is

to

be

written the intensifying waveform is the same in

the

time

interval

'0

to

'l'

whereas

the

amplifier

output

waveform

has

indicated which should be written

well

before

'l'

during

the

strobing interval

'I

to

'2'

Hence

if

the intensifying sianal

to

the c.r.t. grid

is

fed through a gate circuit which is controlled

by the strobed amplifier

output

in such a way that the intensifica-

tionis

turned

off

at

I)

if

the control signal is negative

(or

zero),

but

is maintained until

14

if

the control signal is positive,

the

system will be regenerative in that it will immediately. re-write

everything it reads. This arrangement

is

shown in outline in

Fig. IS. Details

ofa

suitable gate

cir~uit

operated by the

positi~'

control signal appear in Appendix 9.1 .

Itt

bnHl<lllCt

•

.Jwfonn

U:I>l1

hnnkll1C<.'

lI,wef0l'm

Fig.

lS.-A

regenerative storage

system.

In practice it has been found possible to replace the special

time-base waveform, Fig.

14(11).

by

a simple linear time-bue,

provided the duration ratio

of

waveforms

(g)

and

(f)

is

not

less

than

about

2·4

to

I,

and

provided also that

the

sweep speed is

such that not more than

o·

7

of

a spot diameter is traversed during

the short intensification period

of

I·

9~.

The dots

then

appear

as very short lines instead

of

true dots.

The waveform

of

Fig. 14(d)

iso'f

considerable interest

and

will

now

be

analysed in some detail.

Let a horizontal line

on

the c.r.t. screen be produced

by

applying the wavefonn (a)

of

Fig.

16

and its paraphased form

to

the X plates

of

the tube. the grid modulating waveform being

phased as

at

Fig. l6(b). Electron cloud pulses shown

at

Fig.

16(c)

will

of

course provide a part

of

the amplifier output. The

remainder

of

the output. shown

at

Fig. 16(d),

is

due

to

the

following causes. When the beam

is

switched

on

initially,

the

positive well which

is

formed.

is

partially filled as the spot moves

away from the beginning

of

the Jine. This happens

in

all

positions previously occupied by the spot. as the spot leaves them

behind,

and

moving trail

of

positive charge

is

formed beneath

and

behind the spot as indicated in Fig. J 7(b). When

the

spot

reaches the end

of

the line, the beam

is

switched off, the trail

of

.

7

•

II

WJLI...IAMS

AND

m.BVRN:

A STORAGE SYST£M FOR

*'

+---...,....-.v----i'"-

,

....

l'.-AmpIifier

output-pullc with a line dilPlay.

(b)

(c)

(d)

(6

Oriel

-0+':

t,.

..

"'-.

(~

n..

........

ont.

(c EJer:uoe cloud

.,....

(

rw..

due

10

~

08

c.r.t.

1CNeIl.

( .

.-..

.................

U

Spot

-

.--.

o VdlSl +

....

17

.~PotentiaJ

distributions with a

liDa

display.

.

~:~

::-J~I

diatributioa: beem

OD.

(d

Poteodal

dilUtbution:

beuI~.

(4)

Subeequaat potCDtial clilcributioa:

....

OD.

maximum amplitude

of

the

initial positive pulse is

aucb

that

the

trail

of

charae

is completely established

~fore

secoudary

electrooa..beain

to

destroy

the

remanent charae

at

the

e:od

of

the

line.

The

currentsflowiDg

from

and

to

the

pick-up plate

to

produce

the po5itive

and

anticipation pubea, respecti\'eJy,

are

then

entirely separated

in

time.

In

practice, it is found

that

little

1011

in

amplitude

'of

the

pulse occurs

if

the

lenlth

of

a dash

i.

made

IUCb

tbat

the

aepuation

between centres

of

the

initial

and

final

spotl,

which

fonn

tbe lateral boundaries

of

the

dub,

it

not_

than 1·7d. With this value

the

positi\'C and anticipation

puIIes are hePmioa

to.'-'OI.Iesce

as

shown

in

Fia.

18.

FIe

.•

I.-Strobina

'of

lianals.

(II)

Sipab.

(')

Strobe.

(c)

SvobecI

output.

By

way

of

example, the display,

and

amplifier

and

Itrobed

outpUts

appropriate

to

the decimal number

19,

are shown

in

Fi,.

19

(b,

c

and

d).

In

a two-state device either state may be

Fig.

It.-Electronic

binary representation

of

decimal number

IY.

(II)

Binary.

(b)

C.R.T.

display.

(.)

Amplifier

output.

(d)

Strobed

output.

\ defined

as

representing a

"0,"

the other state tepresenting a

"I

.

cbarae

iI

left

on

the

screen,

and

the potentia) distribution is

tben u indicated

at

Fig.

17(c).

Now,

when

the

beam is switched

OIl

apin

at

the

.beginning

of

the

line. a trail

of

charge

has

to

be

recreated,

and

this causes

the

initial positive pulle

of

Fig. 16(d).

Once

tbe

trail

of

clwp

iI

created,

there

is

no

net

change

of

duup

on

the

c.r.l.

ICReIl

until the remanent charge

at

the'

end

of

the

tiDe

ia

approached.

Durina

this period

the

amplifier

output

is zero,

and

the potential distribution is

of

the

form shown

in

Fig. 17(d).

As

the

spot

approaches within

the

critical distance

of

the remanent charge, low-velocitY secondary 'electrons with

component velocities along

the

line begin

to

destroy

the

remanent

charge. Since, when

the

beam

is Iwitched

off

the potential

distribution must again

be

as

in

Fig. 17(c), a quantity

of

surface·

charge, equal

in

mapitude

to

the created trail

of

charge, . is

destroyed during this period. Hence a negative pulse, equal in

area

to

the initial positive pulse, appears

in

the amplifier

output

voltage,

as

shown

in

Fia. 16(d). This negative

p~.

which

anticipates the cause

to

which

it

is due, namely,

the

switching off

of

the

beam, has

been

called

the

66

ant

icipation" pulse.

llMt·ReI..

output

of

the amplifier is the

sum

of

the waveforms (c)

and

(d)

of

Fig.

16

and

is shown

at

(e).

If

the

length

of

the Jine is

dcc.raIed,

the

wavefonn

of

Fig. 16(e) becomes the waveform

of

Fig. 14(d).

~

The theoretical minimum length

of

the

li~

for

..

In

the

present

paper

the digit will

be

said to be

"0:'

when

the

potential distribution

on

the c.r.t. screen

is

the

same

as it

wouk

, be

if

the"

amplifier gave zero output and the gate circuit

acte,,'

appropriately.

(3.3) System

2:

Dash-Dot Display

This

systdb

is

identical with

sys~m'),

except

that

the negati';'

pulse

at

beam switch-on operates a suitable gate circuit jnste;",

of

the positive pulse. The positive pulse now corresponds h

the digit "0"

and

the display is a dash as shown

in

Hg.

20Cc

The negative pulse shortens the dash

to

a dot, and correspond.

to

the digit

"1."

(

L-/3

.,.

•

USE WI11I BINARY-DIGITAL COMPUI'ING

MAaDNBS

89

~

lll~

1

.~t-'

! I r

~

j f t t

f~'

.1

t:)

Fig. lO.-Storaae-system displays.

Ca)

Binary

..

(b)

Dot-dash.

(C')

Dash-dot.

(d)

Dcfocul-roc:ua.

(to)

Foc:us-def'ocus.

(f)

Anticipation.

(3.4) System

3:

Defocus-Foras Display

An

alternative

method

of

achieving' the choice between a

positive

or

negative indication

at

beam

switch-on

i5

to

apply the

waveform

of

Fi,.

21(b)

to

the focus

el~trode

Al

of

the

c.r. tube.

t7)

~l.SU8I'fght.

up

.'

",

I

8I.1ck

OUl

(b)

r.--,

;

~

: n :

r.-

o.rXU1

..J

:

~

;

L;-J

:

.L!-J

:

f;x-U$

• I I I I • t

Fla.

ll.--C.R.T.

electrode waveforms for dcfocua-(ocus display.

(_)

Grid

JDOduI.tin

••

aveform.

(b)

A.2

••

wlorm.

If

waveform

of

Fig.

21

(b) is phased relative

to

the grid modulating

waveform

as

shown, the result will

be

a

defocuse~

spot

which

suddenly

becomes

focused,

as

shown in Fig. 22(cl).

IbIV-

"'T

Fla.

ll.-Potential

distributions 'with focus-defocus display.

(a)

Display. (b) Well

I.

(c)

Well 2.

When the beam is switched

on

for

the first time, well I shown

at

Fig. 22(b) will,

of

course, be excavated by the defoe-used spot.

However~

when the

spot

is focused, the shaded

area

at

Fig.

21(a)

will be partially filled by secondary electrons, producing

the'

potential distribution well 2 shown

at

Fig.

22(c).

At

subsequent

instants

of

beam switch-on it will always

be

necessary

to

convert

well 2

into

well I,

and

a

net

positive pulse will

be

obtained

at

the amplifier

output.

If

the c.r.t. beam is switched

off

before

it is focused, the focused

spot

will never be present,

antt

the

potential distribution is always well I. Once this distribution

is

established. the

output

from the amplifier

at

beam SWitch-on

will

be

the negative pulse

due

only

to

the introduction

of

the

• electron cloud

near

to

the pick-up plate.

The

sign

of

the

output

pulse

at

beam

switch-on is therefore po!\itive

or

negative, depend- .

ing

on

whether the

spot

is

allowed

to

focus

or

not

.

If

the system is

operatc4

on

the

positive pulse, the gate circuit

of

Section 3.2 is used. The only modification is

to

make

the.

time-base

pause

from

I =

'0

to

I =

'.

(Fig. 14). Horizontal

separation

of

the

digits is achieved by allowing

the

timc-basc

to

run

down

linearly

from

I =

I.

to

I =

I"

when

the

beam

current.

is always off. TIle

spot

is defocuscd

from

I

==

'0

to

I

==

IJ and

focused

(or

blacked

out)

from I

;..

t)

to

I = I

•.

The display

appropriate

to

the

decimal

number

19 is shown

in

Fia.

20(d).

(3.

S) System

4:

Focus-Defocus Display

If

the

system in

the

previous section is operated by the

nepti~

pulse

at

beam switch-on, in conjunction with the gate

circwt

required

in

Section 3.3,

the

display will

be

as

shown in

Fig. 20(£».

(3.6)

System

5:

Anticipation

Whenever the

beam

current

is switched-off, a remanent

du.rae

is left

on

the

screen,

and

with a moving

spot,

an anticipatIon

pul~

.

is obtained

during

tho

next time-base sweep.

This

gives a

wamin'g

that

at

some

"later"

instant

during

the

previous sweep,

the

beam

was switched off.

If

the possible instants

of

swiichina

off

the

beam

are

predetermined by a

square

wave applied

10

•

gate circuit. which allows

the

beam

to

be switched

off

once only

after

an

anticipation pulse

has

been received, then

the

system is

regenerative.

For,

01lClC

established, a remanent charae

w.D

cause the

beam

to

be

switched

off

at

the

same

instant

of

C<Kh

successive sweep,

and

the

charge will

be

reinstated

each

time.

The display is indicated in Fig. 20([).

(4) A

COMPLETE

STORAGE

UNIT

Attention

will

now

be

confined

to

system

I,

which is

sum-

matized in Figs.

14-17

and

19.

The

remaining systems. which

operate

satisfactorily

on

a single line

of

digits, have

bec-n

rcjcc1N;

systems 3, 4

and

5, because

of

the difficulty

of

maintaining similar

conditions

of

focus

over

the whole c.r.t. screen. when many

linn

of

digits

are

used;

and

system 2 because operation

on

the

~tfatl\oC:

amplifier

output

is

not

as satisfactory as operation 011 -the

positive pulse.

Horizontal spacing between

the

digits

on

the

tube screen is

achieved by using a linear X-time-base waveform, generated

a~

described in Appendix 9.4. Vertical spacing is achieved

~)

U\lI\tc

a specialized Y shift generator described in outline below,

anJ

in

more

detail in Appendix 9.5. Each horizontal line

contains

32 digits (i.e.

one

word), occupies a distance

of

10

cm

on

the

c.r.t \

screen.

and

lasts for 272 ",sec. The

blackout

period is J4IL'Cl.

The raster

has

32 lines,

and

at

present occupies a vertical distance

of

8

em.

A

10

em

by 8

cm

rectangle

on

the

tube

face therefore

contains I 024 digits

or

32 words, Fig. 2 (see Section 5.3).

The

type

of

Y

Mshift

generation used is intimately

conne~tcJ

with the writing, reading

and

timing properties

of

the storage.

For

not

only is it necessary

to

scan the raster lines sequentially

with

the

object

of

regenerating the stored information; but it is

also essential

to

arrange

that

any line may

be

written in

or

read

011"

as soon as possible after the machine has given

that

instruction,

without waiting for

that

line

to

be

scanned in the regeneration

sequence. A suitable circuit is now outlined.

(4.1)

Y-Shift

Generator

Fig. 23

is

a schematic diagram

of

a Y -shift generator. which

. produces

32

~qual-step

changes

of

potential followed

by

a rapid

flyback. Along the

top

of

this figure

is

a five-stage Sl.:ale-of-two

counter. each stage being triggered from the prevIous

onc:

the

first stage is

~nggered

by the X time base blackout wavefoml.

The

counter

output

waveforms are as shown in Fig.

'!.~(b·fJ.

If

theSe waveforms are

added

in the form 1 x

(b)

-+.

2 .

(n

+ 4

·L-13

Jf

•

WILLIAMS

AND

JaLBl1IIN: A S'I'OIlAGB SYS'IEM FOR

TiJ1l('-be5e

black-out·

waw-form

[24(aj

_

.............

.

PII.

23.-5imp1e

Y-Ihift

paeratDr.

____

~

o·~

•..•••

-

••

--

••

---

n.

Dumbera

ia

.....

lbaa

1lA<-)J

ref"

to

abe

"!3P

..

~

01

••

~

ia

Fi8.

24

.

.,

111111111111111111'

III

1.11

H f n f n

---'

.-.------

--.-oft' or write in •

given

tiDe

0DIy

wheD

its

tum

came

in

the

IC8Il

,~.

cyde.

Tbia cliIability

can

be

eliminated

by

alJocatinl alternate

\If'

lweepleof

the

time bale

to

66scan"

and

.. action" pbaaea

of

the-

t)

system. •

Durina

ICaD

pbaaes,

the

raster

linea

are

IC8IUled

d scquendauy with

the

.ole object

of

reaenentiq

the

stored

information.

Dwinc

action phases any line

in

the

ruter

may

~

J

be

ctw.n

at

wiD,

and information

read

oft"

or

written

in

that

(f)

J line. With this

arranaement

the lines

of

the raster

are

DOt

FII.

14.-Waveforma

of

simple Y-shift generator.

(6

Counter

O.

.

(.f)

Counter

4.

~~

__

out

wa_Oral.

(,.) Counter 3.

(c

Couat«..

(6)

V-shift

(paraphue).

~

Coaater 2.

X (4) + 8 X

(e)

+

16

x

(/),

the desired waveform, Fig. 24(g)

results. With this waveform and its paraphased version applied

to

theY-plates

of

the c.r. tube the single line display

of

Section

3.1

becomes a 32-line raster. Addition

in

the appropriate ratios is

performed by

the

circuit shown

in

Fig. 23, the operation

of

which

is described in Appendix 9.5.

It

should

be

noted, however,

that

the

counter waveforms, Fig. 24,

(b)-(/),are

used

to

switch

careful "weighted" component shifts in

and

out

of

circuit, so

that

the

amplitude

of

the counter waveforms is -relatively

unimportant.

A scan

of

~is

type is entirely adequate for

the

purpose

of

regenerating stored information, provided that the vertical

acparation

of

lines is adequate and the interval between scans

of

a given line is sufficiently short compared with the inherent

memory

time

of

the

~n.

It

would, however, be possible to read

scanned sequentially but

in

the

order

0·,

n, I,

n,

2. n

...

31,

n •

•

ii1i1lifiliiiiilill

lbI

JlIlIUUUU1JU1f

tI

dI

..,

•

Aftlcn

I

~

I

Fla.

1S.-Waveforms

of

improved Y-shift generator.

~

(a)

Blackout.

(b)

Halver.

(d

Counter

0;

(d)

Counter

I.

(to)

Counter

2.

(I)

Counter

3.

td

Counter

4.

(h)

Y -shift

(parapbued).

0, nt 1

...

where n is any chosen line not usually constant b\,(

varying as

the

computation proceeds.

It

is.

however, she,,",

constant in

the

waveform

of

Fig. 25(h), which illustrates

the

rw-

• The

fint

liDe

or

the

raster

i.

called

IiDc

0

fOl'

convenielra.

L-I.3

01

-.

•

USE WITH IIINMY-DIGlTAL COMPUTING MACHINBS

91

Jomi

of

~

¥-Ibif\

~Yeform.

To

produce

this

waveform,

diait

(t,

t)

is

reaenerated,

and

nmembend

by

the

store

the

blackout

~orm

or

Fil.

2S(.)

reeds

a balver,

wbidl

is a iDdcfinjtely.

acaJo.of-two

counter

yiddina

the

waveform

of

Fil.

2S(b)~

1bia

A

"I"

may

be

erased

from

the

store

by

interruptiRa the •

wawiorm

then

operates

the

counter

chain

of

Fia. 23 which

repnerative

loop

during

the

time

that

the

"1"

would

normaUy

cWiven the

wa~orma

of

Fil.

2S(c-g). The balver

waveform

be

reaeoerated. 'Ibis is conveniently

done

by

switchinl

the

abo performs electronic

switdliDI

operations

audl

that

durina

action line

into

the

appropriate

position

and

applyiDl

a,

nep.ti...e

the

an

pbue

of

the balver. waveforms

of

Fil.

2S(c-i)

are

pulse

to

the

suppressoqpid

of

V I

in

the

pte

circuit

(sec'

Fig. 32).

added, appropriately uwcijbted,"

as

before,

but

durina

the

action

Thus,

although

the

control

arid

of

this valve receives

the

positive

pbaae

they

are superseded

by

five

control

voltqes,

which, pulse

from

the

amplifier,

appropriate

to

a dasb,

no

anode

currmt

operatina

tbroup the same "weiahtina" circuits as

the

counter

will

flOw

in

the

valve,

and

the display will

be

converted

into

a

dot.

waveforms, take

over

~ntrbl

of

~

line saumcd. Technical

It

follows

that

the

typewriter

unit

may

either

write

or

erase a

details

of

a

suitable

circUit will

be

found

in

Appendix

9.S.

Here

&61,"

and

that

a sin&le pole,

double·throw

switch may

be

WJCd

to

,

we

need

only

note

the

importance

of

us

ina

a

common

"weightinl

tt

lelect

either

of

these

alternatives.

circuit

so

that

liDe

II

during

action

phases exActly coincides

with

If

the

input

to

the

gate

circuit

from

the

amplifier is connected· -

_

Line

It

durinl

scaa phaacs. .

to

earth

potential

for

a

period

longer

than

a raster period,

then

Though

it

miaht

appear

at

first

sight

that

this

action/scan

the

store

will

be

filled

(dashes

everywhere),

for

pulses will

be

aequence will halve the speed

of

Qllculation,

in

fact

such

is

not

applied

to

the

control

grid

of

V I

durina

~

strobe

Period.

the

case,

because

siDee

it

applies

only

to

the

store,

computation

If,

on

the

other

band,

the

output

of

the

amplifier is disa:mDeCted

can

proceed

,unhindered,

and

further,

some

time

must

be

set

from

the

pte

circuit

for

a

period

longer

than

the

raster

period.

uide

for

chaDgina

the

fiw

potentials

seJcdinI

the

~ion

line. the

store

will

be

emptied.

1beIe potentials must not

be

chanacd

whilst they are

controlling

the

shift,

or

diagonal

·traces will

be

Jenerated,

but

they

can

conveniently

be

cbanaed

during

the

scan

pbuc.

In

a

machine

the

fiw

control

voltqes

would

be

derived

from

a

statidlOr

operated

by

a sequential five-pulse code.

In

the

experimental

ltore

tbey

are

in

fact derived from a staticisor,

but

the

operatinl

pulses are coincident pulaea on five

separate

lines

and

may

be

made

positiw

or

negative

on

each

line

by

setting

five

switches

appropriately. The

pulses

are

obtained

from

the

balver

waveform

and

ocatt

at

the

end

of

each

action

phase,

so

that

the

staticisor

can

only

chanae

its

state

during

scan

phases

when

it

is

not

controllina the Y -shift. . ' .

An

amplified discussion

will

be

found

in

Appendix

9.S.

It

should

be

noted

at

this

point

that

although

the Y

-raster

aenerator, X-time-bue

aenerator,

and

the

ciraJitJ

aenerating

such waveforms

as

the

atrobe

for

the amplifier

output,

are

euential

to

the

operation

of

a single

storage

unit.

these circuits

ape

common

to

aD

further

units.

It

is

only

necessary

to

repeat

the

c.r.

tube,

amplifier

and

pte

circuit, since all

the

c.r. tubes

and

gate circuits will

be

operated

in parallel

to

a

common

time

scale.

For

Jhis

reason,

a c.r.

tube

and

its associated amplifier

and

gate

circuit will

be

called

a "stOJ1!F

unit."

(4.2)

Esperimeiigllaput

Ullit

Infonnation

will eventually

be

introduced

into

the

store

via

an

input

unit,

which

may

take'

many

forms.

An

ex-

perimental

method

of

input,

far

too

laborioW!

to

be

used

in

practice

and

designed with

the

sole object

of

testing

the

storage

unit, is

as

follows. . .

1be

bam

is swiiched

on

32 times

during

one

X-time-base

• sweep,

and

vtith an

empty

store

a negative pulse is

obtained

from

the

amplifier

each

time,

the

display

being

32 lines

of

32 dots.

If

a negative pulse

of

dash

width

is inserted

into

the

gate

circuit,

in

such

a

manner

as

·to

give

the

same

effect

as

a positive pulse

output

from

the

amplifier (see

"write';

input

in

Fig. 32)

and

timed coincident

with

one

of

the

instants

at

which

the

beam

is

switched

on,

then

a

dash

appears

~t

the

corresponding

point

of

the display

and

a

661"

is inserted

into

the

store. If. further,

the

pulse is

gaaeratcd

during

action

phases only

then

the

dash--will

appear

only

on

the

action

line.

'The

circuit

supplying

the

pulses

isartanged

in

such

a

manner

that

pressing

one

of

32 keys,

arranged

in

the

form

of

a

typewnier,

causes a pulse -to

be

generated

at

the

corresponding

instant

of

switching

on

the

beam.

A

"I"

is inserted

in

position k

ofJine

1,

by

operating

the

switches

controlling

the

Y -shift staticisor

so

that

line I is

the

action

line,

and

then

pressing key k

of

the

typewriter.

Once

inserte4

the

(S) EXPERIMENTAL RESULTS

AND

OPERATING

DATA

It

is

now

possible

to

fill

or

empty

the

store,

and,

by

mama

or

three

control

systems, namely, the iD8ert-erase switch,

the

type-,

writer

and

the

Y-shift staticisor,

to

change

the

sta'"

or'di~l

(k,

1).

Specific patterns.

such

as

the

one

shown

in

Fig.

2(11),

.,

therefore

be

written

into

the

store.

in

order

to

test

the

IIleI1I\iy

of

the

storaae

unit.

The

pick-up

plate prevents direct

pboco..

graphy,

and

a

monitor

c.r. tube wired

in

paratJel,

with tile

storage

c.r.

tube

was

photographed.

During

the

initial

.....

many

memory

periods

of

between

oI)C

and

two

howl

wac

recorded.,

By

adding

a

sixth

unit

to

the

Y -shift generator a 64-line

raster

--

was

produced,

and

the

storage

capacity

doubled

(:!

048 diaits).

The

scan

frequency

was

then

about

2S

cIs. 'The

pattern

shOwn

in

Fig. 2 (b)

was

written

into

the store.

and

was "remembered"

for

four

hours

before

the

equipment

was

switcbcd off.

it

is

interesting

to

note

that

in

this

time

approximately

7· S x lOt

opportunities

occurred

for

a

change

in

the

pattern

to

take

'place,

due

to

possible

spurious

pulses

occurring

during

strobe

periods.

The

existence

of

this

multitude

of

opportunities

for

change

may

be

regarded

as a disadvantage

of

frequent regeneration.

There

is, however, a very

great

corresponding

advantage.

In

any

system

where

the

position

of

a

storage

element is defined

in

terms

of

two

multi·

valued deflecting potentials

(or

currents),

subsequent

recovery

of

the

stored

infonnation

depends

on

aC-

curate

correspondence between geometrical position

and

deflect-

ing,potentials

and

also

on

accurate

reproduction

of

the

deftectini

potentials

themselves.

Both

these requirements

are

much

more

easily

met

when

the

interval between storage

and

recovery is very

short,

since long-period

drifts

in

supply voltages.

or~.

tube

sensitivity, result only

in

a

drift

of

the

pattern

as

a whole

without

damage

to

it,

provided

the

drift

between regenerations is small

compared

with

the

spot

size.

The factors influencing

the

operating

conditions used

to

obtain

these

results will

now

be

described.

It

will

be

seen

that

a

com-

promise

has

been

made

between

many

conflicting factors.

(S.

1)

Primary

Electron Velocity

From

Section 2:2

it

follows

that

the

third-anode

voltage

9f

q.e

c.r.

tube

should.

be

such

that

the

primary

electron velocity

corresponds

with

a screen secondary emissian

ratio

greater

than

unity.

With

the

screens used

in

co~1

~.r.

tubes a

further

limitation

is irnp6sed,

and

this

is

now

discussed •

The signal

output

from

the

amplifier normally produced by

scanning

aline

on

the

c:r.t. screen is shown in Fig. J6(e). How-

/1

.

",,-

......

~,..

_

·_·...,L~

.

£.

-13

"

•

.AcceIInl

....

' •

.....

2I.-Vari8daa

or

ICI'em

~

.......

WiLda.

, • 7 •

voltap.

. .

the

iIP"ed~

aiaDals

due

to

aIuI or

........

.....

• .....

tbe

ICCIIeratiDa

voltqe

ia

reduced

to

........

COIl..,.

UltIna

with tile

point

B

in

Fi,.

27

........

dMI

wi

....

t

....

",!I

.'

potcotial barrier. The .....,ailude

01

Chc

~

due

CD

..,~

..

~

w.riy

as the

~tiaa

voIta_ is

deerE

--

tends

to

aro

u the acceIeratinl

voltaae

approada

zero.

,-.

results

wen

obtained with a CVl131 type

0(

C.r.

tube.

wbidt

-....

.a

soft

iJasa

eDveiope,

and

the particular

imperfect_

........

".4tId

weM

the

Jarpat

which occuned

at

&II)

poeM

01

tht

~'

~

c.r. tube baa yet

been

found with

more

than

OM

\.4IIh1f\ '

.....

,f

. imperfection. The number

of

aWl

or

impurity

amper1a

tKmS

with ratios areate!' than

0'1

(but less than

o·

2)

is about twenty

at

1

«JO

volts.

With

tbeIe

restdts

in mind it was

decided

to

ope

.........

......

c.r. tube

at

the comparatively low acceleral.R,

Vi."

.....

ut

1400

volts. The tube was not specially

IC_~.

C''''

Nt

it

had

a hard

alau-

en~)ope,

and

there

was

a

cubon

trnprtf«.-

.tioo

in

the

screen.

'Ibis c.r. tube, which stored the infornwl ..

",

.

for

Fi

..

2,

~

been

uaed

for a period

of

three month.

.•

,-,

00

difliculties

ba~

arisen

due

to

acn:en imperfections.

<5.2) Etl'ed 01 Spot Size

(F--)

1'be ltoraae capaeity

of

a sinale c.r. tube

is

determined pnmarily

by

tho ac:curacy

of

focus,

and

its uniformity over the

UIed

area ",'.

the

tube

tcreeD,

it

beinl

neoctS&I'Y

to

choose

Jess

than

opltJDUm

fOCUl

at

the

centre' if bad defocusing

at

the corners

IS

to

be

avoided.

FOI'

maximum capacity. the tube should

be

operated

at

the

mabest

possible aaeleratina voltage. W

it"

present

~,

die imperfections limit this voltaae

to

I

400,

and it is

apparent that

an

attempt

should

be made

to

produce a more

•

IawnioII

poi8t

anwoaiaalCfy

••

I

2100

yolu. -

/ "

/~.

L

-1.$

•

VIiB

WD1I

BlNARY-DlGrrAL

COMPUTING

MAQIINES

93

pcrf'ect eaeen, with the

cooaequmt

iDaeue

in

atorqe

capacity.

TbiI is

beina

attempted. '

Althouah,

for

CODItaDt

beam

density,

the

amplitude

of

the

positive

sipalsobtaincd

wIleD

the

beam

is turDcd

on

will

dec:reue u

the

focus b improYed, DO dif6culty is anticipated,

because, u Ibown

iftFia.

18,

exc:eUeot

IiaPW/noile

ratio

is

obtaiDed with the Pl'CIIDt

spot

..

(about

I mm

diameter).

u.

of

Jlipal

current may therefore

be

c:ompcDIated

by

iDa'cued

amplifier

pin.

I

M

shown

in

Fi&-

2(b),

2048

cliaits have

been

stored. the atea

occupiedonthestoralCtubebeina

lS4anl(Han

x,

••

an).

In

Fia- 2(a),

the

area occupied

by

I 024 diaits is 64

anl

(10

em

x

6,4

em).

The

deterioration in

the

uriifonnity

or

focus over

the

Iaraer

area can

be

aeen

by

the

fact

that

for

satisfactory

operation-nealigible

interfereoce between digit

areu-the

ara

ocwpied

by

2 048 digits

is

more

than

twice

that

occupied by

I 024 diaits.

(S.3) Adioa

LIIIe

,

.........

01

Stonae

ea.-:ItJ

The conception

or

critical distance between

two

adjacent spots

cannot

in

fact be applied without reservation

as

it

was

in

Sec-

'lion 3.1,

to

determine.

the

separation required between

any

two

charpd

areas

of

a raster

for

nealigible mutual interference.

For

the

net electric field

at

a

spot

under electron bombardment is

Ilt)

lonaer due

to

a

sinale

adjacent charged area,

but

to

all the

remainin,

cbarpd

an:as

of

tbe

raster.

It

follows

that

the

required separation is greater than

the

critical distance previously

defined,

and

this is particularly

true

for

the

~

comprising the

edaes

of

the

raster,

whe~

the

net

lateral electric fields

are

patest.

The

method adopted

to

determine

the

required separation

'.

experimentally is

to

adjust

the

focus,

and

separation between

areas, until

the

relevant positive signals obtained

at

any

point

"

of

the raster, are

not

decreased by more

than

5 % by mutual

~

._

terference, when adjacent

dots

are converted

to

dashes. It is

found

to

be

sufficient

to

examine areas

in

the

comers

and

centre

r

the

'raster only.

"

Since

a small

amount

of

mutual interference between adjacent

cbaracd areas is allowed

to

occur, the time

of

bombardment

ot

the areas

becomes

important. particularly when this time is

only

of

the

order

of

I~.

(The

time

of

bombardment

of

the

areas

is

determined by the velocity with which

the

spot travels

~

the ·c.r.t. screen. This velocity is discussed in the next

SectipP.)

It

may

be

seen,

for

instance, from ·Flg.

13

that, in

the

double-spot experiment, bombardment times less

than

2

p.sec

prod~

but little filling

of

the adjacent well.

If,

then, some

areas f the raster are scanned more frequently than others.

more-

utual interference will occur in these regions.

This

will

happen

~hen

the

~tore

is part,

of

a computing machine

and

it

is

necessary

to

read

or

write into the store frequently during

one

raster period, for under these circumstances

cenain

lines

of

the

raster will be scanned more often

than

other

lines. _ With a

32-line raster,

and

the method

of

raster generation described in

Section 4

and

Appendix 9.S, it is never possible

to

scan a

particular line more than

33

times as often as the adjacent lines.

For

in

one

raster-period this line would

be

scanned once during

a scan period,

and

32

'times during action periods

at

most.

To

determine the extra degree

of

separation between digit,

areas

required

to

nullify this effect,

the

following procedure

~as

adopted.

It

was arranged for the c.r. tube

to

be normally

blacked

out

-by halver waveform during action periods. A

circuit triggered by the waveform

of

the last counter in the

Y -shift generator.

and

re-triggered

by,

halver waveform pro-

hibited this black-out for

one

action period during each raster

period.

The

action line was therefore scanned only twice as

often as

the

remaiqing lines. This arrangement was used

to

VOL.

96,

PART

~II\

\

,

write

the

information shown

in

Fig. 2 into

the

store,

and

provides

a close approximation

to

haviq

no

action line whatever.

The

control

of

black-out by

halwr

waveform

was

removed

and

the

action

liDo

scanned during every action period.

The

extra

vertica11epar&UOD

was then detennined.

It

was found

that

when

this was

done

the

area

occupied by the raster bad

to

be

increased

by

20%

(10

an

x 8

an)

for

a 32-line raster. This is a very

stringent test,

because

it

is incooceivable

that

it

will

be necessary

in

practice

to

read

or

write

into

one

particular line durina

32

CODICCUtive

action periods.

An

increase

of

20%

in the area

of

the 64-line raster

(II

em

x

17

an)

allowed any particular line

to

be

scanned

eight times only

durina

one

I'8$ter period. mainly -

because

rapid

deterioration in uniformity

of

focus

oCcurred

with

this large raster area.

(S.4) I.atenI VelodtJ

.,

tile FJectro.

...

The time period assisned

to

each digit. whidl

at

present is

8· S

p~,

determines the final

speed

at

which the

computin.

machine will operate. This time period, which should therefore

be made

as

small as possible. depends

upon

the maximum rate

at

which the electron beam can be allowed

to

move acroD the

c.r.t. screen.

It

is

apparent

that

the

faster the electron beam

moves, the less will be the amplitude

of

the positive pullC

obtained when the

beam

is switched

on

at

the beginning

of

a dash.

For

the amplitude

of

this pulse is determined by the amount

of

refilling

of

the

well

which occurred durina

the

and

the depth

to

which the

weU

is excavated during the present

sweep. Since. as was explained in Section 2.4. refilJina rcqulm

more time

than

excavation. the speed

of

operation

is

limited

primarily by the refilling

pr<X.'nS.

Less refiOin,

wiD

occur n

the

speed is increased, because the electron beam bomn.-rJs

adjacent spots for less time.

and

lhe amplitude

of

the

~itive

pulse therefore decreases.

An

estimate

of

the speed

at

which some decrease in amphlude

may bcexpccted. can be derived from the double-spot exp.:rimenl.

From

Fig. 12. the limits

of

separation between which maximum

a:efilling

of

the adjacent well

occun.

are seen

to

be

d and I -I

bJ.

From

Fig. 13(c). refilling

of

the adjacent well

is

seen

to

be

almost

complete in 4

p~

at

the operative value

of

beam current

If

therefore, the'diameter

of

the

spot is 1

mm

and

the spot travels

at

speeds

greater

than

0·04

mm/p.sec

some

loss

of

po.)itivc pulse

amplitude is expected.

As

the speed is increased, the pulse obtained when the

beam is switched

on·

at

the beginning

of

a dash

ch41naes

from a positive pulse

to

a negative pulse via stages similar

to

those shown in Fig.

13

(c,

b,

and

a).

Fig.

29

10 in which

both positive and ru!gative amplitudes- are plotted, indicale\

the change in the amplitude

of

the pulse as a

fU.1ction

of

the reciprocal

of

the

speed

with which the electron

beam moves across the c.r.t. screen. The point A

~orr\!s~nds

with the speed estimated above.

If

the speed

is

increas~

by a

factor

of

ten, approximately, the point B is obtained. This

IS

the operating point used

at

present

and

it corresponds with

8'

5

,...sec

and

3'

I-mm digit separation.

If

the speed

is

increased

by a further factor

of

ten

(4

mm/j.LSCC),

the positive pulse

ceases

to

exist.

and

theroutput pulse is the negative pulse due

to

the

electron cloud' effect.

It

is.

of

course, impossible

h)

operate the

storage system

at

this last speed because the pulse obtained when

the beam is switched

on

will always be negative

ind~p.:nd.!nt

of

whether a

dot

or

a dash

is

being read. However, it

mJY

prove

possible

to

operate the system

at

some point between

Band

C,

the speed

corr~sponding

with C being twice the present

speed.

It

should

be

noted

that

Fig. 29 holds for particular values

of

brilliance

and

focus only, the values chosen b.!ing the ones

normally used in operation.

7

•

L.-13

•

....

2f.-Variation

with

sweep

w:Iocity

of

~

anduced

wbaa

the

......

illWitcbcd 011

..

eM

..........

oIa

dIIb. .

U.5)

......

kill

Recapitulating, it

mutt

be

possible to diatiqu.iIb' between

two

typeI

of

sipal,

wbidl COIiespond

to

two

types

or

atond

charte

dilCributioD.

The

area

oa:upiId

by

the

dicit

&Na,

and

the

time

..

iped

to

each

dJaft

are IDIde •

smaU.

u possible

CODIistent

with die

maiDteDaIM:e

of

this distinction.

·In

the

clot

.....

.,..aIm

the

c:boia: is between a

poIitift

or

a

neptiYe

sianaJ

wbeD

the

c.r.t.

beam

is

awitcbed

00,

and

the

amplitude

of

there

lipalt

...

hdl

upoD

flld.ors dilculed

~

and

in

Section

2.

The

liDe

of

immediate future deYelopment is

dear.

ImproYo-

ment

of

focus

aID'

be

attacked

from

the

oormaI standpoints.

Final

raults

wfU

depcDd

00

the

production

of

a more perfect

1CRIeII, and

the

.....

t IDaeue

in

aaderatina

wimp.

If

this prowa

difficult.

KNCIII

or

the

preaent quality,

but

free from

carboa, depoIieecl OD

lOme

Dulator

(such u mica) with a

higher

iDWftioD

point

than glass,

may

be

1UCCeIIfuI.

Hisher

storqe

capacity

per c.r.

tube

will

then

be

possible. When the

maximum

ItOrqe

per

tube

hal

been

oblaiDed

the

required

storap

capacity

can

be

built

up

by

UliDI

the

appropriate

number

of

tubes.

AU

tobel

would

be

KaJU'1ed

syncbronously.

but

the

actioo line

would

be

intensified

only

on

the

appropriate

tube

10

that

the

co-ordina",

of

an

individual

stored

digit

becomes

k,

I,

t, where

t

it

the

tube

DUmber.

(6) ALTlRNA11VE SCANNING SYSTEMS

The

acannina

sys1lem

So

far described is

most

suitable for

series

machina

in

wh.idl

one

complete word is stored

00

each line.

Machines deaiancd for

the

parallel mode

of

operation require

aU

the digits

of

a word

to

be

simultaneously available

on

different

wires. Workinl

on

a basis

of

32 digits

per

word. 32 c.r. tubes

might

be

used,

one

digit

of

each word occupying

one

space

on

each tube. With Uti! arrangement. the diaits occupying the

32nd space in

each

line would

not

be

available for 272 p.tcc.

This

tirnecan

be

reduced

by splitting

the

scan

into

8 colunms

of

Fla. 30.-Alternative

sCannina

arranaemcnt.

short

lines. each containing 4 digits, as shown

in

Fig. 30, arrange-

ments being

made

to

re,d

any

digit

in

any

line

at

any

time .

..

This

would reduce

the

time

to

obtain.

any

digit

to

34

~.

AJtemaUWiIy,

tile

time

sweep

...

,

...

boIiabed

aDd

replaced

"by

a deflectioo

lianal

.-rator

wIaidl

it

at'I'aDIId

to

aweep

...

IPOt

·dilcoDtinUOUlly

from

IPICC

to

II*»

OIl

the

c.r.l

&oe

by

means

of

appropriate

X and Y

voltqea.

Provided the deIec:tDa

..-..or

could

be

IWitched

to

any

cIeIiIed

co-ordinatel rapkIIJ

-any

diait

could

be

RICO\'eRd

at

..,

time.

T'be

approprialt

co-ordinatea

could

probably

be

____

ted with

the

requiNd

8CIanCJ

in

about

20

fItICC.

(7) CONCLUSION AND ACKNOWLItDGMKNTS

It

baa

t..l

demonstrated

tbat

....

II1JIIIt.. 01 diP"

caD

be

stored

OIl

the

screen

of

an

ordinary

co

...

_c:iaI

c.r. tube

and

that

the

deYelopment

of

special

tut.

for

....

purpose

it

wortb

punuiq

and abouId

lead

to

an

iar

..

III

IIOrqe

caPKitJ

per

. c.r. tubc. .

1'be

authon

wish

to

actn~

their

iDdeMed

_

to

till

Olief

Superintendent,

T.R.E.,

'for

facilities

pro~ided

durina

the

researdl,

and

to

Prof.

M.

H.

A.

NewmaD.

F.R.S

.•

and

Mr.

A.

M.

Turin&

O.B.B.,

for

much helpful

~

or

the

matMa

.'

requirement.

of

diaital

computer

storeI.

,(8)

RQI'I'll&Naa!I

(I)

VON

NIVNANN,

J.: Unpublished

wdrt.

(2)

TuaIMo,

A.

M.:

Unpublished wort.

(3) WILKIB,

M.

V.:

.-n.e

F..niac-Hiab-SPeed

EIecuoIuc:

(

.•

culatiDa

~

..

&ctrolrk

~,

April

,

..

.,

19,

No.

230.

(4) BuJta,

A.

W.:·

..

Electronic ComPUtiaa CtrcWtI

oIUW

Eniac,"

~6

0/11w

hull".

of

.RAtIio

~

1947,

35,

p. 756.

(s)

HIDtANN.

W.,

and

G!YIIt,

K.:

EkkttVcJw

AIel

.......

Tecltnik,

1940.

17,

p.

1.

(6)

McGa,

J.

G.:

··EIectronic Generation m

TeIeviID

Sianals," "FJcctronics" edited

by

B.

lo¥aI

(

............

Ltd.). .

(7Y

McCoMNEu..

R.

A.:

"Video

Storage

by

Secondary

em...

from

Simple Mosaics."

ho«141f1J

(»{

,,.

la,,;,.

."

Rodio

EngiM~I.

1947.

35,

p.

12S.

(8)

BaUINING,

H.:

"Sccondary Electron Emillion,"

",."..

Teclurlcal

RnIew,

March

193',

3,

p.

Ikl.

(9)

RUDBDO.

E.:

PItY$IC6

Rni~.

1936.50, p.

138.

(10)

BoARDMAN.

E.:

Unpublished work.

(II)

WILI.1AMS,

F.

C.:

"Introduction

to

Ci.mJlt

TechRiQ'"

t

Radiolocation~"

Journal

I.

E.E. , 1946,

9.~.

Pw\

til-

p. 303.

(See

Section~

9.2-9.4.)

(9) t-PPEND1CES

(9.1) The ADlpIifter

Each

stage

of

the amplifier is separately screened.

and

-.

beater

and

h.t. supplies

are

fed

to

each

staF

throuah

knt

....

filtered

leads

to

prevent h.f, oscillations. Tbese

arnm

......

-

are

omitted

from

the

circuit

shown in Fia. 31.

The

first

tb.n=e

stages. which are

id~tical,

are fed

bad

b

resistor

of

SOO

kO

connected between

the

anodc

of

V

3'

and

f.,.

pid

of

VI'

The

feedback, reduces

the

cffect

of

micro,""",

voltages in

Vito

negligible

proponions,

and

defines the '''''P''

voltage

of

V 3

as

O·

5;, volts, if i,

is

the

signal

current

in n."ro-

amperes

provided

by

the

pick-up plate.

The

fourth stage

I"

,')n-

trolled

by

its screen-grid voltage to give manual galn-COlifrol.

The

anode

lOad

of

the

fifth stage

is

very much greater than

the

,

input

impedance

of

the

sixth stage, Consequently. almc".

"n

the pulse current, delivered

by

V5,

flows in

the

J3-kU

t'cedh.Jd

resistor

of

stage 6. Stage 6

is

d .c. fed back. as shown, to

provkk

outputs

with approximate d,c. le,'els

of

either + 5

'oIolla

or

-

IS

volts.

1'1

•

£.. -''':>

\

USB

WI11f

BlNARY-DlGITAL COMPlJTlNG

MAaDNa

-}&Ov

.....

31.-

The amplifier circuit.

va-v,

~

CV1091.

V.

-CV113.

The

voltqe

outpu&

of

the

amplifia' is UJOI.wbal

the

~ua1

is set

10

that

the

voltaac

pia

or

tile last three

Itqes

is 200.

The

dou~

aperi.meotl

...

paf'0IIDDd with tbia

letting.

.

(9.2)

G.-.

CIraIIt

Referencee

wiD

be

made

to

Fia.

32.

The

eWeet

of

this cin:uit is

to

provide

the

arid

of

the

c.r.

tubc

with

narrow

positiw

pula.

td

ai~

a standard display

of

doll

300

V

Input

from

D4~'

~~~

.

amplifier

VI

D3

\

<-ISV)1

O-O}L.'-'~:':':~:4-~~~"-"

__

4-_'"

Dl~

0

Strobe

Erase

Dash

Read

Dot

input

iRput

input.

(-lOY)

(OV) tOY) (+4Y) (+4V)

•

Fla.

31.-The

pte

circuit.

VI-V.

-

CVI09J.

Writ.e

input

(+4Y)

conaponding

to

the

digit

'-0";

these

pulses are

made

wider,

prodocina

a

dash

corresponding

to

the

digit

"I"

if,

and

only

if,

the

circuit receives a positive pulse

from

the

amplifier

at

specified

instants,

the

instants

at

which

the

beam

is switched

on.

The

standard display is provided by

narrow

negative dQt pulses

[Fia- 33(d)] applied

to

the

cathode

of

the

diode

06,

the

cathode

beina biased positive

with

respect

to

its

anode.

The~pulses

cut

off

the

control

grid

of

V

3:

and

the

anode

of

V

J.

w.hich was

bottomed,

rises

Quickly. in voltage until

caught

by

the

diode

07

at

about

+

SO

volts. The

resultant

anode

waveform

shown

dotted

at

Fig.

33(f)

is

cathode

fonowed by V

4'

and

applied

to

the

c.r.t.

arid

via a d.c. restoring circuit, whic:h defines

the

highest

voltage reached

by

that

grid,

as

the

voltage set

up

on

the brilliance

control

of

the c.r. tube. Black-out

of

the

X-time-ba~

recovery

sweeps is provided by

the

fact

that

the

dot

pulses

.Are

IllhJbited

at

• •

Fla.

33.---Waveforms appropriate

to

pte

circuit.

-,

.

~

(d)

A,mplifter

OUCIIUI.

(d)

'Dot wavefone.

(0)

Strobe.

(,)

DbIa

..

~

•.

(c)

VI

anode.

(f)

(Mpur

'e

u.t.trid.

their

source

during

the

black-out

~iod

This

i!

all()

tr\ll

of

the

dash

and

strobe

pulses.

~

valves

VI

and V

lt

and

their

anociate4

diode!. are t'-'

true

gate circuit.

1be

amplifier

output,

...

JI,

J~\~J.

bla!Cd

10

-

15

volts, is fed

to

the grid

of

V J only

during

the strobe period.

At

all

other

times this is provcoWd by

cond~ion

of

0,

11k

strobe waveform is shown

at

Fig.

33(b).

the strobe period being

a

short

period immediately after the beam

is

switched on. There

is normally

no

anode

current

in

VI'

Olnd

the anode vo.taae

IS

defined as +

SO

volts by the diode D2•

The

anode

waveform

Fig. 33(c)

has

a negative pulse for every

pc:xiti\'C

pulse c1ehverw

hy the ainplifier during a strobe period.

"The

negatl\e

pulses are

cathode

followed by V2 via the diode 0 ••

and

applied to the

control

grid

of

V

3'

The

upper

\oltagc

limit

of

the control

gnd

of

V 2

is

defined

as

0 volts by conductJOn

of

D.

and

OJ.

and

its

lower limit

is

defined

a!-·

15

\olts,

by conduction

of

Ds. .

The

cathode

orv

2

wiU

therefore

~wing

In

voltage between the approxI-

mate

limits

+-

3 volts

and

-J

~

volts, which are sufficient

to

cause

full

anode

current,

or

no

anode

current. respectively, in VJ. The

condenser

taken

from the control grid

of

V 1

to

earth

prevents

the

grid changing its voltage unJess it is driven.

The

grid

will

therefore remain

at

-

15

volts for a period. the dash period,

determined

by

the

waveform

of

Fig. 33(e) applied to the

anode

of

Ds.

It

will

then

be

driven

to

0 volts

and

will

remain

there

•

L-/3

"

UDtil

it

naiwI

aDOtber

aepti\le

puIIe

(rom

tho

anode

of

V

••

PiI-

18

IboM

the

practical equiYaJea1l

or

tho

idealized

wa~

forma

or

Fia.

33

(G.

b"and c).

The

action

of

the

dn:uit

iI

IIJIIIIIIatizec

as

follows.

If

the

diapIay

at

a certain &pot

00

the

Cor. tube

was

previously a dot, a

__

dYe

puIIe will

be

deIiwred

by

the

amplifier

duriq

the Itrobe

period,

wbal

tbe

IpOt

II

bombar~

apin.

smce

the controllrid

olV.

is normaJJy

c:ut-oJr,

the.,..tiYe

pul8e

has

n'o"oct.

aDd

the

.

pte

drc:uit

it

iDoperati\le. A

dot

is therefore produced

ap¥l

by

the

dot wawfonn.

D,

and

V

J.

The

comspondini wawforms

ant

Ibown

by

the

dotted lines.

in

FiJ.

33.

If

the

display

wu

~

a

dub,

a poIitive pulIe from

the

ampijfier aiw.

rill

to

anode

cuneIlt

in

VI.

The

resuItiDa

neptiw

pulse

at

the

bode

orv

••

takcI

the

arid

0(

V 2

to

-

IS

volts when

it

rcmaiDa

until dri

..

bKt

to

0 volts by

the

dub

wawform

IICtina

throuIh

D,.

The

arid

orv

J

it

then:(ore

cut

off

Initially

by

the

dot

wa\'eo

faim

and

beId

off

Cor

a

dub

period

by

the

cathode

or

V

2'

npoduciDa

the

dub

display.

A conWllieot

"read"

output

for

the

storqe

unit

II dcriwd

hID

the cathode

or

V

2-

and

it

takes

the

form

or

a

aepti¥e

puIIe

or

dash

width

for

cadl Itored

"I:'

ExtcroaI information.

fepleMDted

in

this

1DIUIDeI',

can

be

written

into

tho

ItOrqe

unit

by

appIyiDa

it

to

the

c:atbode

of

D..

Each

ucptivepulle

extmds

a

dot

into a

dub.

When

writina

DeW iDf'ormation

0\IeI'

old

information,

it

is

abo

DeCeSIaI'Y

to

conw:rt a

dub

into

• dot.

ThiI II

KbieYed

by

applyina a nepti\le waveform

to

the

~

lOr

arid

of

V.' which cuts

08'

the

anode

currcmt

in VI

duriq

the

writiDa

period, breaks

the

re,eaerati\le

loop,

and allows

c0m-

pletely DeW information

to

be

inIerted via D •.

(9.3)

'Be

Clock CIradt

The

clock circuit,

wbidl

produces

the

I·

S-p.sec

digit cycle,

comprises

an

LC

OICiUator.

squan:r,

and

cathode

follower.

The'

ItrObe

and

dot

and

dash

waveforms

are

produced

from

this square

..w

aDd

fed

to

the

pte

circuits from low impedance sources.

Two pbantastron circuits

in

aeries, dividiDa four and nine

~,aretrigered

by

the

dock

waveform.

Tbe

outputs

0(

the

pbaDtutrous

are

used

to

produce a square wavefonn, which

is positive

for

4

dock

periods.

and

negative

for

32

dock

periods.

'Ibis

it

the

X-time-buc

bllck-out

waveform,

and

it

is used

to

control tho X·tiD»-bue circuit

and

Y -shift

pnerator.

The circuits

UIed

are well known,

and

JequUe no detailed

delcription.

. (9.4) X Tiaae-Bue

QaIt

1bia

circuit is a Miller

time-bue

followed

by

an

anode-

foltower

ciJaUt

to

provide

the

parapbue.

A linear sweep is

produced

startina

at

a potential defined

by

a diode.

The

alternative sweep for dot-dash storage, shown in Fia. l4(h)

O·Ol#,lP

(!-u-_

.........

--....

.'

Dot,

~

w6'leform

a

Dot.

waveform

applied

to

I\.

E~'

-4V

f

rate

Rat.elc~

....

34.-GeDeration

of

time bale with

pa~

durina dot period •

paUleS

duriq

the

dot

period. 'Ibis is

achieYed

by

retumina

the

tiJDe..bue

arid

leak

to

the

dot

waveform

and

d.c.

restorina

the

wawCorm with

an

inverted diode

to

a potential equal

to

the

mean·

arid-poteotial

during

the

sweep

(Fia.

34).

I>urioa

the

dot

periOd

DO

cumm

80Wl

in

R

and

the

rate

of

sweep is tbaef'ore zero.

If

E is

the

amplitude

of

the

dot

..

wform

the

rate

of

sweep

at

all

ott.

times

is

EIRe.

Tbe sweep

requinK1

for

focus-defocus

storaae

pauses

duriDa

the

..

period, and

il

achieYed

as

above by usina

the

dash

wawiorm

iDs&ead

of

the

dot

wa~.

.

(9.5)

Y-s1118 G

......

R.elei'aas

wiD

be

made

to

Fia.

23,

which is a

achematic:

diqram

of

the

silnple Y -shift

____

tor.

A10na

tho

top

of

thiI

fipR

is

the

fi

...

taae

scaIo-of-two COUIlta',

each

I.

beiDa

trigered

from

the

previous one:

the

first

slap

is

trigered

by

the

X

time-bue

bIack-out

wawform~

Each

c:ouoter

D

(n

=-

0, 1,2, 1

or

4)

is associated with a triode Tn

wb.ic:b

bas

a

resistaDcc

RJ2rt

in

its

cathode

lead, and

the

cathode

or

the

'triode is

connected

via a diode

On

to

the

arid

of

a pentode

called

the Y -shift val

....

1be

output

of

the

Y -shift

valw

and

its parapbascd version-

are

applied

to

the

Y -plates

of

the c.r. tube.

1be

circuit is complCltid

by

triodeI

T.

whOle cathodes are also

connected

to

the

raiItin

RJ2a.

For

the

~t

it

win

be assumed

that

the

CUl'I'alts

ill

tbeae

triodes

are

cut

off

by

ueptiw

voltaIC'S

E,,:

The outputs

of

the

counters 0

to

4

areu

shown

in

Fig. 24

(~/),

and

if

thae

are

added

toptber

in

the proportions I, 2, 4, 8,. 16 (Le.

2--

1)

~Iy,

then

the

resultant

output

is the step

waveform,

FiJ.

24(r)~

Thia step

wawform

is therefore

the

output

vol

...

0(

the parapbue

of

the

Y -shift valve, since

eadi

time a triode

T.

is

cut

off

by

the

ueptiw

aOina

half-cyclc

oftbC

waveform

of

counter

D,

a

CUI'l'eDt

proportional

to

2"/R

flows

into R

throuab

D..

The V-shift

valw

operates as a fed-back

addinacin:uit,t

addiq

contributioaa

from

R/2"

whenever

D.

conducts.

R'

it

chosen

to

giw

suitable Y -shift. . . :

It

follows

Cram

the

above

discussion

that

if

the grids

of

the

triodes

T.

have

neptive

voltqes

applied

to

them,

Which.

aR

suflicient

to

cut

off

the valve currents, then the line

of

the

,.....

scanned

by

the

time-bue

can

be

mo.en

at

will by applYm.

suitable

voltqes

E"

to

the triodes

T;.

For

Ell

can

be

chosen

to

that

Do

either does

or

does

not

conduct

(25 possibilities),.aad

It

D.

conducts a contribution

2"

is made

to

the line number.

If

for example, with the convention

that

the first line

in

the

~

is called line 0,

it

is desired to scan line 21, then EJ

and

E)

aft

made positive

and

Eo,

E"

·and

E

..

are made negative. Only

thr

diodes

DOt

D"

and

D

..

conduct

and

a Y-shift of21

(20

+

21

+ 2.,.

units is produced.

It

will.be observed

that

the line chosen

b:--

'

operating the triodes

T~

and

the

corresponding line

of

the raster

produced by

the

triodes T a

are

accurately the same, since

thc'Y

..

both

depend

on

the

~jstors

R/2D

and

not

on

the triodes involved.

provided the triodes are actuated

by

sufficiently large potential"

1be

requirement for

prompt

execution

of

an

instruction

h~

reading

or

writing leads to the division

of

the raster operation

into the two phases called

"scan"

and

"action,"

control

beinl

exercised by wavefonns applied

to

the grids

of

the triodes

T.

and

To.

1be

modifications necessary to make

the

circuit

of

Fig.

2.\

confonn

to

this requirement are shown in Fig.

l5..

Here

black-out wavefonn triggers a halver circuit, wfuch, in t

triggers the five-stage scale-of-two counter, the wavefo

volved being as shown in Fig.

25

(a-g).

The halver ci it is

itself a scalc-of-two counter.

The

halver waveform

is

(led

to

each

of

the counter waveforms,

and

the' resulting w eforms.

Fig. 36, (a-e). are applied _

the

..

ids

of

the triodes T fier being

•

Parapbue

is

~

..

w

or

uodo-follower

circuit.1

t RdCreoce

II.·

. 9.2. .

/6

....

•

....

-'-'

VSE

WI'I1I BlNARY-DIGrrAL COMPVTING

MAaDNBS

To

V-shift,

------?-~~------~~~~~~~~~~~~~

vAlve

grid

Negat:.ive

pip

valve

Fla.

35.-1mproved V-shift

ItMrator.

The IlUJllben

ia

brKkets

thus

{~{G)J

rerer

to

tbe

waveforms

a.bowa

ill

tbe

c:orr.poadi....,

_bercd

Fipra.

~.c.

restored

to

earth potential.

In

other words. the greatest

~oltage

achieved

by

any

of

the wavefonns. Fig. 36.

(a-e).

is zero

/volts. Further. the wavefonns have sufficient amplitude

to

i PftVent current flowing in the triodes T D except during those

half

I cycles

of

the halver waveform during which they are

at

zero volts.

I Now.

if

it is assumed for the moment

that

the potentials ell

, applied

to

the triodes

T~

are sufficiently negative to prevent

current flowing in

T~.

it will

be

seen that during the first scan

period (Fig. 36) current flows in all the triodes Ta.

so

that

the

diodes

D.

do

not conduct.

the

Y shift is zero

and

the electron

beam

of

the c.r. tube scans line

O.

But during the first action

period

no

current flows in any Ta, so all

Do

conduct, the Y shift

is

at

its maximum value and line

31

js

select~.

During

the

second scan period only

Do

conducts, so

that

unit shift occurs

and

line 1 is scanned. During the following action period all

the diodes Dn conduct again,

so

that line

31

is again selected.

It

will

be

clear from such consideratipns that the whole raster

of

32

lines will

be

scanned sequentially, line

31

being the action line

o

ScaT"

I;

Scan

2

action

I",

{action

2 OYJ .

(0)

p,J9j--

SCAn

3;

aet,jon3

-,

Gnd

base

OY..;

(b)

JUl-vUlt'Lut[

-,

OY..;

(c)~

t

OYJ

(d)~

-,

qy,

(Q)~-'.

UUUUTIULJuuliuu

(iVl.L ..

{

(i)mnnnn.nft+0n~n#lnl#ntL0

___

~0Y...t

(f)

(ii~1fU1JlIUl

_oTto ••

()

J(i)~

g \(ii)

rrrnrrrrY

Fig.

36'

(a)

Halve,

+ counter

O.

(d)

Halver

+ count"" 3 .

.LIt}

Halver + counter I.

(,)

Halver +

counter

4 .

(~

Halver +

counter

2.

(f)

HaJvcr, phase 2 (}fa)'

(6)

Staticisor

triuer

pips.

between scans

of

adjacent linea.

The

V-shift

waw(onn

will

be

as

shown

at

Fia.

25(11)

except

that

here line 10

it

belDl

!CIccaed.

In

order

to

seJect line 10, say, appropriate positive

IT;

conductina)

and negative

(T~

non-ronducting) voltages,

~,..

IbouJJ

be

applild

l50kO

-150V

--t----!t-.----

+ 100 V

Fig.

37.-Circuit

of

stage

"of

Y-shift generator.

•

••

•

L-/3

-.

"

II

'WJLUAMS

AND

m.auRN:

A SI'ORAGE SYSTEM FOR

to

the grids

of

T,.

during

the

action periods only,

since

these

voltqes

must

not

interfere with the scan, i.e. with the voltages

applied

to

the grids

of

Ta.

To

select

line 10 requires a shift

of

10 units durina

the

action periods ooIy,

10

that

during those

periods

eo,

e2

and

e"

must

be

positM

and

e1

and

e3

negative.

Henc:e

if

the

waveform (i)

of

Fia. 36(f)

iI

used

for

eo.

e2 and

e"

and

waveform. (0)·

of

Fig. 36(J)

for

eJ

and

e3~

line 10

will

be

selected. Here

the

opposite

pbale

of

the

hal\Ier

to

the

one

previously considered is used,

ana

is arranged alternately

to

switch on

and

cut

off current in

T~

at

(i),

or

is biased well beyond

cut-off

at

(iO,

Fig. 36(j).

One

cycle

of

the shift waveform

under

.

these conditions is shown

at

Fig.

2~(h).

In

order

to

change the action line, the

d.c.lema

of

the

wave-

fonDS

ell

must

be

changed from 0 volts

to

beyond cut-off

of

r.

or

vice versa. These volta

..

must

not

be

changed during

an

action period, because,

if

they

ate,

a diagonal line will

be

traced

across the

scnen

by

the

electron beam.

and

stored information

will be wiped out. 'J'hey

may,

however,

be

changed

at

any time

during a scan

Wiod,

since they only affect

T~

which plays

no

part

in

the

operation

during a

scan

period.

It

is convenient

to

arrange

that

a

change

in voltage can only occur at the

beaiDnina

of

the

scan

period immediately following the throw

of

a switch.

To

achieve this. either the positive

or

the negative pips

shown

in

Fia.

36(g), which occur only

at

the beginning

of

scan

periOcII.

are applied

to

the

input

grids

of

five

flip-flops by

means

of

ftw

switcJa.

This

arrangement

is

shown

at

the

bottom

of

Fig.

3~.

When

a switch is thrown.

the'

corresponding flip-flop

QDQOl

change its state until

it

receives a pip. This ensures

that

c:hIaIt

of

state can

neYa'

oc:cur

during

an

action period.

The

positiw

or

negative voltaaes produced

by

the

ftip--ftops

are

added

to

the

balver waveform by anode follO'Nen

to

produce the

waveforn

of

Fig. 36(j).

StalC

II

of

the

schematic diaaram

of

the V-shaft generator

shown in Fig. 35 is reproduced in schematic form

on

the left

01

Fig. 37. Details

are

shown in corresponding positions

on

thr

right

of

the

fiaure.

DISCUSSION BEFORE

DIE

MEASUREMENTS

AND

RADIO

SECI10NS,

lND

NOVEMBER,

1948

Dr. A.

M.

Uttley: Prof. Williams started this work a

few

months before he left the T.R.E.,

and

I should

like"

to

refer

to

developments carried

out

at

the

Establishment since his de-

parture.

It

is stated ill

the

-paper

that

there

were

five different

ways

of

using

the

principle

of

the

dug

and

partially-filled well.

and

I believe I

am

right

in

saying

that

before

the

work

went from

T.R.E:

to

Manchester

the

anticipawry-pulJe method

'of

storalC

was being used. TIle dot-and-dash method was later adopted

in Manchester.

At

the

T.R.E.,

we

built a store

based

on

the

same principle as the author's,

but

having certain differencel .

]n

May, 1948, we completed ,a

serial

store containing

1024

digits.

The

positive-

and

ocptivc-going

waveforms

can

be

Been

quite

ckarly.

I believe, however,

that

it

is wrong

to

represent

o by

the

absence

of

a pulse.

We

are

hoping

to

do

our

computiq

Work with a positive pulse for 1

and

a negative

pulse

for

.0.

Many relay computers use both .• 0 relay

and

a 1 relay. rather

than

an

UDoperated

relay

to

mean

O.

Checking

of

all digits

then becomes possible.

To

this

end

of

a three-state computer,

we have mod.ifiedtbe

pting

Qrcuits,

so

that

the

positive-going

wave detected

at

the

moment

of

switching

on

of

the

~

causes

one trigger cin:uit

to

SO

over,

and

a

ncptivc-going

wave triggers

anotl1er circuit; the combined

output

of

these two trigger circuits

gives· a positive

....

miaosec pulse .for

1,

and

a negative-soing

pulse for

O.

This has

not

converted storage into a complete three-state

system.

We

have

to

switch

on

the beam

to

find whether there

is a 1

or

a 0 there,

and

there

arc

only the two states.

the

excavated

or

the

partially-excavated well.

For

three-state computing.

therefore, this

is

only a temporary measure.. We

hope

and

believe

that

truly

three-state storage will

one

day

be

achieved.

Needless

to

say.

our

routing, adding

and

trigger circuits are all

three-state. .

Another way

in

which

our

work is differing from

that

of

the

authors,

and

deliberately so, is

thai

we are hoping

to

complete

a parallel

ari~tica1

machlnc rather

than

a

..

ial machine.

This results in

an

interesting change in the use

of

the cathode-

ray tube.

If

one cathode-ray .tube is used

to

store the least

significast digit

of

1 024 different numbers.

and

the next tube

to

store the next most significant digit

of

I 024 different numbers,

and

so on. then,

in

order

to

read

one

number, all the cathode-ray

tubes in

paralleillave

to

be switched

to

corresponding points

of

the

Same

X-V co-ordinates

on

all the tubes; it

is

then possible

to

take

out

simultaneously all the digits

of

a number.

In

between the actions

of

reading from,

or

writing into.

the

store,

we

interleave moments

of

rel)lCDCration.

Oilits

are regenerated

sequentially as

in

a television scan. but between

th~

momeftt,

the

store

can

be

used

at

any

point.

It

is possible to

·lCMp

frOf'

point

to

point in a quite

random

manner;

our

e'tperiments su

....

that

the time taken

to

move

from

one

point

to

an),

other is

hUt·

to

be

about

10 miaosee.

)

am

sure

that

it

is generally realized that the authoa.

.,.

..

tint

to

have sua:ecdcd in

mak.ina

a practical

,tora..,

system f

....

electrOD.ic

computers. Such variations

as

those t have

u.

doocd

only emphasize the fundamental aclUevemcnt

~retIIft"'"

by

their work.

".

Dr.

F.

AIIIIatIe:

How

did the authors discover. the

,lor.

property described

in

the

paper;

was

the

Jltur.-.r"

IU

....

.ac.'X:.1

dental,

or

was

it

based

on

any theoretical

reasoruna?

J'J.

have

prodUQCd

what seems

to

be the

tnt

~

...

-,'t:'",~JlI!

."tr~_

digital storage device.

,";

'The

authors suggest

that

there are

five

methods

ofusina

,_

basic storage property.

but

it

seems to !''\Iot

lI,;,'

tlv

.~

....

and

dash-dot methods

are

essentially the same,

'\I~

(n,

,...,

in

which

of

the characters is

used

to

represent

1.

This

,,-.

tinction is

not

a fundamental one,

becaUK,

U'

~

!Mae

~~.

the respective representation

of

1 and 0 may

t..

.HHelen.

10

different parts

of

the machine. The

Ymt'

comment

appl~

to

the two focusing methods, so that it seems

to

me that

.M"Y

three different methods are descnbed 10

the

parer

Do

the authors confirm that in Fig.

L\

Ule mpu\

/I

nltM.lnce

....

of

the amplifier is

Jow

compared with any

of

the resastan..a

..

R/16, etc.?

If

this interpretation

''I

Uti

10..:1,

,ht'v

have used

current

and

not

the more

common

voltage

swrundtuUl.

What

was their reason for this choice?

Mr.

W.

P.

Anderson: Devices depend.

n~

for their operation

on

secoodary emission have been

used

10

the radio tield for

many years,

but

they have always

had

rather .1_ bad reputation.

mamly owing

to

the large

and

unpredi\.:table variations in their

characteristics which are liable

to

occur.

It

appears. however.

that

the storage tube described

by

the authors should escape

these difficulties as, being

an

on/ofl device, its operation should

be

unaffected by large variations

an

the secondary emitting

properties

of

the screen material.

This equipment

is

a good example

of

the value

of

a realistic

engineering approach

to

a problem. undeterred by the com-

plexity involved, when this complexity is due only to the extensive

application

of

known techniques. In a comparatively short time

, it has been brought

to

the point where it can be used as a

part

If

"'

....

L-J3

•

lJSB Wl'I1I

BINARY-DIGITAL

coMPU'I'ING

'MAOIINES:

D~JON

99

.

of

a

laraar

project,

while

simpler

and

apparently

much

more

'0·

S

mm/microsec

and

SOO

such

elements were

stored

on

20

an

l

elegant solutions,

such

as

the Haeft"

tube.

are

still

in

the

early

or

the

available

l00cm

2

of

the

storage-screen

area.]

stqes

of

deveJopmcot.,

Mr.

R.

Benjambl: I believe

that

the technique described in the

There

are

many

possible uses

for

oJectronic

storage

devices,

pa,er

has

applications

of

great

value

not

only

to

eomputors,

but

outside

the

computina

field,

which

do

Dot

require

the

storage

also

to

any

other

electronic devices which deal with

the

sorting

of

such

a

Iarae

number

of

elements.

At

what

point

would

it

and

handling

of

classifiable information. The

apParatus

be

worth

while to

cbanae

over'

from

a

bank

of

simple flip-flop described has the

panicular

merit

or

giving a storage capacity

circuits

to

the

stora(le tube?

comparable

to'

that

of

many

highly-specialized storage tubes,

I

should

like

to

know

whether

the

si,nal/noise

ratio

in

the

although

it

WICS

only

simple

and

readily available components.

amplifiec which

handles

the signal from the

pick-up

plate

sets The

authors

state

that

"an

electronic device

cannot

think."

• '

the

limit

to

the

accuracy

of

the

system.

It

would

be

expected

This

appears

to

be a practical

statement

rather

than

a funda-

that

a signal/noise

ratio

of

12

db

would

result

in

an

error

rate

of

mental

ODe.

It

should

be possible

to

construct a device which

about

I,

in

I 000 000.

could

extrapolate

from

past

experience in dealing with present

Mr.

M.

V.

Needham:

At

Borehamwood

we

have

carried

out

problems,

provided

it

had

sufficient

memory

capacity; thus,

the

some

experiments

that

had

been suggested by Prof. Williams's

authors'

work

might

tum

out

to

be a step towards the provision

earlier

work;

they

have

been

confined

to

the

anticipation-pulse

of

a limited

amount

of

automatic

th61ught.

method

referred

to

in

the ,paper

as

system

S.

The

authors"

It

seems

that

the

cloud

effect sets a limit

to

the 'speed

of

indicate

that,

becaUle

of

non-uniformity

of

focus

over

the

whole

operation

of

the

apparatus

described.

It

might be possible

to

storalC

surface, they

have

rejected

this

method

in

favour

of

reduce this effect

either

by using less steep-fronted grid-modu-

system

1.

We

have

used

a CV960

cathode-ray

tube

and

have lating .puises,

or

by feeding

the

differential

of

these pulses in a

not

found

this

non-uniformity

of

focus

to

be

the

limiting

feature

suitable

manner

into

the

video circuits. It also

appears

tha.t

the

in

the

use

of

system

S.

The CV960

tube,

however,

does

enable

•

variations

of

the

electrostatic field towards

the

edges

of

the

•

more

uniformly focused

raster

to

be

obtained

than

does

the

raster

are

one

of

the

limitations

of

the

total storage capacity

VCR97

tube. I

should

therefore like

to

know

in

what

way

of

the

tube.

Might

it

be possible, by

means

of

a

guard

rin,

Don-uniformity

of

focus

is

more

serious

with

system S than

with

external

to

the

tube

envelope,

to

reduce these effects?

If

special

system

l.

tubes

are

developed for this application,

should

attention

be

T'here seem

to

be

several fundamental differences between

the

given

to

keeping

the

thickness

of

the

glass envelfJlSe

constant

"anoos

methods

desCribed

in

the

paper.

First,

in system I

the

over

the

ra~ter

area,

and

to

minimizing variations

of

the angle

of

beam

is

normally

switched off,

and

indication

of

the digit values incidence

of

the electron .beam? •

o and 1 is

made

by

switching

on

the

beam

to

make

dots

and

With reference

to

the relative merits

of

the alternative systerm.

dashes

respectively.

This

means

that

it is possible

to

write

into

at

tint

si&ht it

appears

that

the

anticipation-pulse

method

would

or

read

out

of

the

store

at

any

digit position

without

loss

of

offer a

neat

way

of

utilizing the storage

phenomena.

In

par-

time.

In

system

S,

however,

the

beam

is normally switched

on

ticular. it seems

to

be

independent

of

the

c!oud effect.

and.pemaps

to

produce

Ii

continuous

trace

or

raster.

A transient signal-

also

to

penn

it

some

reduction

of

both

the

time

and

the'-space

plate

output

occurs

at

each

end

of

a line

which

must

die

away

occupied by

one

digit. I should

be

grateful

if

the

authorscouJd

before

the

trace

can

be

used for storage.

This

involves a waste

provi\k

more

information

on

this point. " :

of

time

and

space, which

can,

however,

be

reduced

to

a

minimum

Dr.

R.

A.

Smith:

It

seems

at

first sight

to

be

very

re~able

of

one

digit

period

per

line

if

a suitable

raster,

such

as

the

that

the first

material

chosen

for

making

~se

experiments

on

Z-scan,

can

be

used. electronic storage has

proved

to

be

so

very successful. The

Secondly.

if

system 1 is used,

what

is

in

effect a digital

scan

commercial cathode-ray

tube

has

the

very

great

advantage

that.

can

be

used,

and

digit positions

can

be defined by

means

of

preset

when something is written

on

it, it

can

be seen

as

a luminescent

voltage increments.

In

system 5, digit positions

must

be

defined trace;

but

it is by

no

means

obvious

that

the

screen.

materi~lof

in

a

more

indirect way by

means

of

the

scanning

rate

and

digit a

cathode-ray

tube

is

the

most

suitable material for electronic

periods. .

,-

storage. A

moment's

thought,

on

the

other

hand, convince<i

The

third

point

of

difference

concerns

speed

of

operation,

and

one

that

it

is

at

least

not

unreasonabh:

to

suppose that such

in

this

connection

some

measurements

we

have

made

may

be

material would be suitable.

It

has

a fairly high' secondary

of

interest. A single trace was produced

00

the

storage

tube,

electron emission,

and

it

has

a fairly high. but not

too

high,

and

a small element

of

this

trace was blacked

out

to

obtain

an

resistance;

sO

that,

although

fairly good short-time storage

is~

anticipation

pulse followed by

an

excavation pulse.

This

latter

~btained,

one

does

not

get the paralysing effect

to

be expected

p~

is identical

with

that

produced

by

the

dash

of

system I.

from

a very

good

insulator.

From

that

point

of

view, therefore.

It

was

found

that

the

excavation-pulse

amplitude

falls

with

the

materials

nonnally

used in

cathode-ray

tubes have the charac-

increasing writing speed, whereas

the

anticipation

pulse increases teristics likely

to

be

required for such a storage system.

to

a

maximum

and

is still

of

usable

magnitude

when the

other

It

is

obvious

from

the

method

of

operation

which the

authors

is

quite

small. These results suggest

that

the

anticipation-pulse

I\OW

use

that

it

is

no

longer necessary to look

at

the tube;

one

method

might

be

usable for

shorter

digit times

than

is

poaible

examines

what

has

been written

on

a separate monitor tube, so

with system

1.

A possible

explanation

of

these curves

may

be

that

there is

no

need

to

use a

phosphor

for the screen material.

that

the

anticipation

pulse is unaffected by the cloud-effect pulse

It

would therefore

be

interesting

to

learn whether any

other

types

~rring

at

the

commencement

of

the

break.

whereas

the

of

material have been used for storage;

excavation pulse is always offset by

the

negative-going cloud-

Mr.

P.

G.

Redgment: I should like

to

enlarge

on

Mr. Ander-,

effect pulse

produced

at

beam

switCh-on.

son's

reference

to

the signal/noise ratio.

If

a true

random

[The speaker showed a film illustrating

the

use

of

the

distribution

of

noise voltages is accepted. it

can

be

only a

matter

anticipatjon~pulse

method

for

the storage

of

pulses

on

a circular

of

time before a false pulse is injected into the system, so that its

s6ln,

which

was

foundcanvenient

in the initial work,

and

then

practical use

in

a

computing

machine dealing with lengthy

on

a conventional television-type raster.

The

film showed

problems

will depend

on

the

tim~

in which a given probability

stored

patterns

made

up

of

elements

of

2-microsec

duration

with

of

the

occurrence

of

a mistake

will

be

reacheJ. In any circu-

2-microsec intervals between them.

The

writing speed was

latory

storage system this time

appears

to

depend

on

the

'lIIf.;';'--

L-"13

.,. . ,

~

.. '.I- 100 WILIJAMS

ANi>

JW..B1.JRN:

~'S"YS1ZM

FOR

USB

WD1I

BlNARY-DIGITAL COMPU11NG

~OIINES:

DISCVSSION

•

siana1/noise ratio. In the

~

of

the

men:ury-delay line

type

temperann

on

the

shape

and

penisteace

0(

the

potential

well?

it

acems

that

the

output puIIe may

poIIeII

qualitiel-«lcb

u an Althouah anaIope computation is

not

Itricdy within

the

terms

accurately

controUed

.wid~wbicb

enable

it

to

be distinauilhed,

of

the paper, I should like

to

mention

u.t

""

bave

been

experi-

fiom

noise

and

tbemore

improve

the'

sipaJ/noiJe diIcrimiDa- meotina

ad'

a store for anaIoaue information,

using

a modification

tion. The cathode-ray tube

storap

systems delcribed

provide

Of

the

priDcipie delcribed. Briefty. a trail

of

char8e

is

depoIited

a rather odd-ibaped

puJse,and

it

aecms

that

not

much cin:uit on a catbodo-ray

ICI'een

by a '-writing" spot.

It

is

subiequeody

dilcriminatioD

from noile, other'thaD

that

liven

by the time

at

scanned

by

a raster,

and

the

pulaes.

detected

in the nwmer die

whidl

the

pulse occurs, can be

obCaiDed.Whether

dle

"antici- authors have deacribed, are

used

in

the obvious way to reproduce

.,.tory

puIIe."

or

the

"weD

aDd

weI1..fi11ina"

type

deiCribed by

the

the written waveform via a flip-ftop

or

a strobe circuit. With

authors. is

u.d,

it

eema

,that some importance must

au.dl

to

this,

anaqement

it is perhaps more important

than

with

the

liPaIInoile

ratio,

as

it

may determiDe the ultimate

accuncy

dilital

method

to

reach the limits

of

definition,

and

it would

be

whicb the

computor

can

adlieve with any

8iwn

Iia

01

problem.

of

interest

to

know what.relevant cft'ect.

if

uy,

is produced'

by

Mr.

D.

M.

MKKa,:

Is

anytbina

known 01

the

iDftuence

of

cM.nJCS

in

the

temperature

of

the

pboIpbor.

11IE

AUIlIORS'

REPLY

TO

11IE

ABOVE DISCUSSION

PNI.

F.

C.W

.......

and

Mr.

T.

KJIINrn (i"

"ply):

We

shall

not

attempt

to

answer

speakers

individually,

but

will

attempt rather

to

COYer 'most

of

the

points

railed in

the

di8cussion.

Our

knowledae

of

the history

01

this

type

01

ltorap,

apart

from our

own

development,

is JaraeIy

...

on

beanay.

As

far •

we

know the discovery

that.1ipaIs

symptomatic

of

be

obeerw.d

011

an

ordinary

cathode-ray

tUbe

wu

'made

accidentally

at

the Radiation Laboratories,

Boatoo.

U.s.A

.•

durioa

some expcrimmta with a special

atoraae

tube.

~

experiments did

DOt

expote

the

vital fact that

sipals

wcreavailable from the

pick~up

plate in4*mty

of

time

to

permit

0(

~on

on a

siDaIe

tube.

AI

rqpuda

.the

taeeIl

surface

material.

it

is

or

coune

moat

CODWlliait

to

UIO

COIJUDCI'Cial

tuba,

but

it

...

CODfideady

expected

that

a

f~

experiments would

~

• prefcrabk

surface.

Experimen1a

have

been

made

iD

a continuously-

evacuated tube with· various kinds

of

.....

aeveral fluorescent

and

other powders,

~d

with mica; DOGe

of

the materials tested

was

u satisfactory

as

the

ordinary

.....

or

blue

ICI'eeIl,

but it

may

well

be

that

the

technique

of

testina

ia

DOt

yet adequately

developed, extreme cleanliness

bein.

of

peat

importance

ill

studyinl

lClCiODdary-emission

effects.

·.A

The number

of

Iystems

described in the paper is

five

or

three.

dependinl OIl

whether

or

not

the

pte.

dn:uit

is

reprded

as

part

of

the l)'ltem. It is

qreed

that

only

iluee

charae CODfiaurations

are

delcribed.

The

choice

between

tbeao

was made

at

a fairly

early

stqe

in favour

of

the dot-dash

~t,

because the

timina

of

the indicatina pulles

was

cloaely

controlJed, because

the

shape

of

thcac

pulses

was

leu dependent

on

focus.

and

becauSe

thil

system was felt

t(J"

be IDOI'e flexible in

that

it could

also be applied

to

parallelltoMS.

We

arc

very interested in, and now agree with,

the

statement

that in

seria-typemadlines

the anticipation 'pulse method

it

essentially'

fater.

It

1CeIIlI, however.

that

since

the

waveform

shown in

Fi

••

J4(d) is

!devant

to

either

systern;-~

the space

per diait will be

the

same for both

systemS.·..

It

aeems

-.

likely

that

botbtime

and

space

per diait can be

improved

by

the use

of

the

fOCUl-defocus

method.-

The

sianal/noile

ratio

of

the

systems

we

have operated

haS

been

10

lood

that

we

have paid scant attention

to

calculatin.· the

probability

of

enor

from this callie. The caJculation is a diffi-

cult one

since

allowance must be made for

strobinl

and for the

fad

that a

aoile

pulac must exceed

the

datum level for a certain

period. before it becomes effettive. Some rough calculations

bave

DOW

been

....

and indicate that failwe from this cause

should

not

oa:ur

more than'orx:e

in

thirty

centuries

o(-con-

tinuous

runniDa.

10

that

the scant

reprd

paid to this

pomt

therefore appears

to

be justified.

It

may

weU.

be

that

it

is

sounder enaineerina

to

~t

zero .

."

a sianal rather than by the absence

of

a

sipaJ,

linc:e lJeIO

it

ewry

bit

a .vital a

~picce

of

information

as

l.

Our attitude.

boweYer-and

this is relevant

to

the

two previous items as welt

-hal

been that

we

would

proceed

for the time beina with

the

limplesteaentiala

of

the

machine, since

ft

feel that

some

experience

of

the actual operation

of

a madline is quite

'Utaent

at

this

stqe

of

the

development.

We

should like

to

thank

Dr.

Aughtie for

the

co~tions,

com-

municated

to

us privately. which have been incorporated ip ·the

paper,

and

confirm that we have, in

f~ct.

used

current summAtion.

the

IUIOft

beinl

that

in general

we

reprd

this procedure

as

both

. simpler

and

more elegant than voltage summation, whicb

usuaU),

calls

for sublcquent amplification. .

It is

interatinl

to

see

from Mr. Mackay's remarks that

the

storaae property has

some

application also

to

analogue com-

puten.

We rearet that

we

have

no

information about

tty

dfect

of

lemperature

on

definition,

It

is difficult

to

state

at

precisely what point it becomes

eco~

mical

to

use c.r.t. storage instead

of

storage

on

flip-ftops.

If

a"','

cathode-ray tube is counted as equivalent

to

10

valves, then in

a series system taking valve numbers alone as a criterion,

the

c.r.t. system is preferable for any number

of

digits in

excess.

of'

3~,

but it is recognized that the flip-flop system might be

m()re

reliable

and

might therefore

be

used for numbers not too

greatt~

in excess

of

32 digits.

--------~-----.--

----------

-"---

---.

-

---

._-

•

ERA 1101 F11 Storage System

ERA-1101-f11-StorageSystem ERA-1101-f11-StorageSystem

Navigation menu

Versions of this User Manual:

Views

Navigation