ERA 1101 F11 Storage System

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

User Manual: ERA-1101-f11-StorageSystem

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(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
dpea~:I!IMI~ ." .........'.,...'

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of"...

.', (1.1)' 'III!t.

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....., ',"" ., PI•• , ..

Tbe~'ol. . . . tIiIiIal~""the.,mecr
~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- .

iDa ItaDdpoinf,

~ spoo.deoQC

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may be ~blished between each
of the device
or die diait. The' number of values which a

aDd eadl value

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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 computina mach ina. I, 1 although in the past the decimal system has

bOea \IIed.J.4«

- 0

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Systems of numbers may be derived from the common series:

a._.IJra-1

+ ... ,+ .... + a,bl + tJobO

(h)
'C

which repreaents all intelen with " siaamcant' figures. The
FII~ l;~;~.~llCli~.
dccinial systaD, (or example, is obtained jf b = 10, and -the a's
(a) SedeI: ~ .....;~9i;~:" ebaaDeI •.
are allowed any one of the vaI~ ,between, ,and including, 0
(.)PuaIId: pu1Ie 00'. . .· . . . . . . '
"
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 , equivalea.t of the Dumber 19' being used as All example. In tbC
X 21 + 1 x 20 ~ the binary scale, which can ,be writtc.. 10011
Figure. video pulses are'uaed for. digital repreIeIltah9n. and at
with the least sianificant figure placed on the. right.
Fig. j (a) .the least signifiant figure, is plaQed on the left, so that
The decimal, or binary, POint is OD the immediate right of the time can be shown increasing from left to right in the conventiOnal:
term tJobO. The series can be CQIltinued to the right as follows: 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 "~
Prof. WiWama &ad Mr. KJlbUl'll are at the UaiversitJ ot Mancbestcr.
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WILLIAMS AND KILBURN: A STORAGE SYSTEM FOR

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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 indistinguishable 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 introduced 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 thermionic 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 complex than existing two- or ten-state devices. are the main justification 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 information 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 supersedtng 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 related to 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 arrangement 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)
'k'·

(h)

(,I)

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I "~I ,1 ..':01'
: 0":."" dl~IL'"

face \\hen 'itm'age is in rlllgrl.':-.... In Fig. 21n) there an! J2 lir.
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('
c~lch

i.-/3
IJ
100 MO. The voltase output from the amplifier is. then. I volt
per hundredth of a microamp of current ftowina
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.

to:

PICk - up plate
1 - - - - - 0 Output

' - -_ _...J

FII. 3.-DetJtion or lianaJa.
common duumel, as in the iconoscope. This method of detectina changes of charge on an insulatina surface has also been UIed
to determine the ICCOIJdary emission ratio of insulaton usina
pulse technique.'
.
Havin. formed a general picture of the rep...,.tation of digits
by a two-dimensional array of suitably cbarlCd aras, attention
wiD now be confined to the small area of the screen correspondinl
with a sinJle digit. The potential distributions existin. on thia
area with different types of electron bomhaJ"dlnent. and the
resuitin. video sipals that ate obtained from the -'p~filf'plaelt-'
are dac:ribed below. Referma:s to literatuJ'e6. 7 on the subject
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 as shown in
9

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

(2.2) Pot6iIdaI I>JIbiIJutbI db Steady SiIIIIe Spot
In a c.r. tube which has its deftector plates; internal con-

ductive coatiq, and first and third anodes all connected to earth
potential. and its grid, cathode and focus electrodes connected
in a normal manner with respect to a neptiyc poteDtial (say
- 2 000 volts), the inner surface of the ICReD will also be a'
earth potential, because it is in contact by Ieaka,e resistance witb~
the internal conductive coating. ~ia ~~ &bat no beam
current has been preSent for some tlrne.·~ In the typea of
co~ c.r. tube invcsti~~ (CV~097 and CVl13I).~
relation between secondary cmtsslon ratio of the tcrecn material
and primary electron velocfty is of the form shown in Fil· S.·

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
To am"ltf..'r
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
r
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
Fla. 4.-Amplifier input circuit.
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. Expcrithe 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 (ep + 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 (CL + 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 +'Cp )' 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
(0)

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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

(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 introduced 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

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.

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! I I~'I""'·
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(C)

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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

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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
(a) Dot display.
(d Strobe.
(/) Dot brilliance waveform.
such that not more than o· 7 of a spot diameter is traversed during
(b~ Dot waveform.
(c Dash display.
(g) Dub brilliaDce waveform.
the short intensification period of I· 9~. The dots then
(d Dub waveform.
(It) Time-b... waveform.
appear as very short lines instead of true dots.
periods of constant rate of change. If a repetitive waveform of
The waveform of Fig. 14(d) iso'f considerable interest and will
this kind, containing, say, 32 such segments is used to deflect a now be analysed in some detail.
c.r.t. spot, which is intensified only during the periods of constant
Let a horizontal line on the c.r.t. screen be produced by
voltage, by applying wavefonn of Fig. 14(/) to the control grid applying the wavefonn (a) of Fig. 16 and its paraphased form to
of the tube, then a row of 32 dots will appear on the screen. the X plates of the tube. the grid modulating waveform being
Two of these are shown at Fig. 14(a). If the separation of thC phased as at Fig. l6(b). Electron cloud pulses shown at Fig. 16(c)
dots is in excess of 1 . 33d, each can be used independently as a will of course provide a part of the amplifier output. The
,storage spot, the beam being used to operate on each one in remainder of the output. shown at Fig. 16(d), is due to the
turn. TIle corresponding amplifier output wavefonn shown at following causes. When the beam is switched on initially, the
Fig. 14(b) goes negative at the instant of switching on the beam, positive well which is formed. is partially filled as the spot moves
as stated in Section 3[a(i)], since there has been no bombardment away from the beginning of the Jine. This happens in all
of spots in the vicinity between successive bombardments of the positions previously occupied by the spot. as the spot leaves them
ltorap spot. If the intensifying wavefonn is changed to behind, and moving trail of positive charge is formed beneath
Fig: 14(g) the dots on the C.r. tube will change into short lines or and behind the spot as indicated in Fig. J7(b). When the spot
"dashes" (see Fig. l4(c»). The initial dots are spaced by about reaches the end of the line, the beam is switched off, the trail of .

WJLI...IAMS AND m.BVRN: A STORAGE SYST£M FOR

•

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

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.

.... l'.-AmpIifier output-pullc with a line dilPlay.
(~

n..........ont.

(6 Oriel -0+': t,. .."'-.
(c EJer:uoe cloud .,....
due 10 ~ 08 c.r.t. 1CNeIl.

..-.. .................

( rw..
(

U
.--.

Spot
-

FIe.• I.-Strobina 'of lianals.
(II) Sipab.
(') Strobe.
(c) SvobecI output.

(b)

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
(c)

•

oVdlSl +

(d)

.... 17.~PotentiaJ distributions with a liDa display.

. ~:~ Poteodal
::-J~I diatributioa: beem OD.
dilUtbution:
beuI~.

(4) Subeequaat potCDtial clilcributioa: . . . . OD.

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
Fig. It.-Electronic binary representation of decimal number IY.
of the tiDe ia approached. Durina this period the amplifier output
(.) Amplifier output.
(II) Binary.
is zero, and the potential distribution is of the form shown in
(b) C.R.T. display.
(d) Strobed output.
Fig. 17(d). As the spot approaches within the critical distance
of the remanent charge, low-velocitY secondary 'electrons with
\ defined as representing a "0," the other state tepresenting a "I .
component velocities along the line begin to destroy the remanent
In the present paper the digit will be said to be "0:' when the
charge. Since, when the beam is Iwitched off the potential
potential distribution on the c.r.t. screen is the same as it wouk
distribution must again be as in Fig. 17(c), a quantity of surface·
, be if the" amplifier gave zero output and the gate circuit acte,,'
charge, equal in mapitude to the created trail of charge, . is
appropriately.
destroyed during this period. Hence a negative pulse, equal in
area to the initial positive pulse, appears in the amplifier output
(3.3) System 2: Dash-Dot Display
voltage, as shown in Fia. 16(d). This negative p~. which
This systdb is identical with sys~m'), except that the negati';'
anticipates the cause to which it is due, namely, the switching off
of the beam, has been called the anticipation" pulse. llMt·ReI.. pulse at beam switch-on operates a suitable gate circuit jnste;",
output of the amplifier is the sum of the waveforms (c) and (d) of the positive pulse. The positive pulse now corresponds h
of Fig. 16 and is shown at (e). If the length of the Jine is the digit "0" and the display is a dash as shown in Hg. 20Cc
dcc.raIed, the wavefonn of Fig. 16(e) becomes the waveform of The negative pulse shortens the dash to a dot, and correspond.
(
Fig. 14(d). ~ The theoretical minimum length of the li~ for to the digit "1."
66

•

L-/3
.,.

•

USE WI11I BINARY-DIGITAL COMPUI'ING MAaDNBS

~ lll~
t:)

f
t
t
f
~
'
j .1
Fig. lO.-Storaae-system displays.
(d) Dcfocul-roc:ua.
(to) Foc:us-def'ocus.

Ca) Binary..
(b) Dot-dash.
(C') Dash-dot.

(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.
. '

(b)

r.--, ; ~ :
I

8I.1ck

.L!-J :

f;x-U$

n : r.- o.rXU1

..J : ~ ; L;-J :
•

" ,

•

OUl

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.

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 =
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).

.~t-'r
!

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 .

(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
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
pin 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
. amplifier VI

\ <-ISV)1 O-O}L.'-'~:':':~:4-~~~"-"
Dl~

Fla. 33.---Waveforms appropriate to pte circuit.

D4~'~~~

__4-_'"

Strobe Erase Dash Read Dot Writ.e
input input iRput input. input. input
(-lOY) (OV) tOY) (+4Y) (+4V) (+4Y)

• Fla. 31.-The pte circuit.
VI-V. - CVI09J.

conaponding to the digit '-0"; these pulses are made wider,
prodocina 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 and the anode of VJ. 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 V4' 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

•

(d) A,mplifter OUCIIUI.
(0)

Strobe.

(d) 'Dot wavefone.

(,) DbIa . . ~•.

(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 Vlt 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 VJ 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 D 2• 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 V 2 via the diode 0 •• and applied to the
control grid of V 3' The upper \oltagc limit of the control gnd
of V2 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 orv2 wiU therefore ~wing In voltage between the approxImate limits +- 3 volts and - J ~ volts, which are sufficient to cause
full anode current, or no anode current. respectively, in V J . The
condenser taken from the control grid of V1 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 ••

•

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( V2 to - IS volts when it rcmaiDa
until dri. . bKt to 0 volts by the dub wawform IICtina throuIh
D,. The arid
J it then:(ore cut off Initially by the dot wa\'eo
faim and beId off Cor a dub period by the cathode
V2'
npoduciDa the dub display.
A conWllieot "read" output for the storqe unit II dcriwd
hID the cathode V2- and it takes the form a aepti¥e puIIe
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 c0mpletely DeW information to be inIerted via D •.

PiI-

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
orv
trigered from the previous one: the first slap is trigered by the
or
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
or
or
via a diode On to the arid of a pentode called the Y -shift val....
or
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
(9.3) 'Be Clock CIradt
T. is cut off by the ueptiw aOina half-cyclc oftbC waveform of
The clock circuit, wbidl produces the S-p.sec digit cycle, counter D, a CUI'l'eDt proportional to 2"/R flows into R throuab
comprises an LC OICiUator. squan:r, and cathode follower. The' D.. The V-shift valw operates as a fed-back addinacin:uit,t
ItrObe and dot and dash waveforms are produced from this square addiq contributioaa from R/2" whenever D. conducts. R' it
.:
..w aDd fed to the pte circuits from low impedance sources. chosen to giw suitable Y-shift. .
It follows Cram the above discussion that if the grids of the
Two pbantastron circuits in aeries, dividiDa four and nine
~,aretrigered by the dock waveform. Tbe outputs 0( triodes T. have neptive voltqes applied to them, Which. aR
the pbaDtutrous are used to produce a square wavefonn, which suflicient to cut off the valve currents, then the line of the ,.....
is positive for 4 dock periods. and negative for 32 dock periods. scanned by the time-bue can be mo.en at will by applYm.
'Ibis it the X-time-buc bllck-out waveform, and it is used to 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
control tho X·tiD»-bue circuit and Y-shift pnerator.
The circuits UIed are well known, and JequUe no detailed D. conducts a contribution 2" is made to the line number. If
for example, with the convention that the first line in the ~
delcription.
is called line 0, it is desired to scan line 21, then E J and E) aft
. (9.4) X Tiaae-Bue QaIt
made positive and Eo, E" ·and E.. are made negative. Only thr
1bia circuit is a Miller time-bue followed by an anode- diodes DOt D" and D .. conduct and a Y-shift of21 (20 + 21 + 2.,.
foltower ciJaUt to provide the parapbue. A linear sweep is units is produced. It will.be observed that the line chosen b:-- '
produced startina at a potential defined by a diode.
operating the triodes T~ and the corresponding line of the raster
The alternative sweep for dot-dash storage, shown in Fia. l4(h) 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"
O·Ol#,lP
1be requirement for prompt execution of an instruction h~
(!-u-_.........--....
reading or writing leads to the division of the raster operation
into the two phases called "scan" and "action," control beinl
.' Dot,
~
exercised by wavefonns applied to the grids of the triodes T.
w6'leform
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
Dot. waveform
volved being as shown in Fig. 25 (a-g). The halver ci it is
applied to I\. E~'
itself a scalc-of-two counter. The halver waveform is (led to
-4V f
each of the counter waveforms, and the' resulting w eforms.
Fig. 36, (a-e). are applied _ the .. ids of the triodes T fier being
rate

I·

•

Rat.elc~

.... 34.-GeDeration of time bale with pa~ durina dot period•

• Parapbue is ~..w or uodo-follower circuit.1

t RdCreoce II.·

9.2.

.... -'-'
....

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
achieved by any of the wavefonns. Fig. 36. (a-e). is zero
/volts. Further. the wavefonns have sufficient amplitude to
~oltage

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.

•

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

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)~

(d)~

OYJ
-,

qy,

(Q)~-'.

l50kO
-150V

(i)mnnnn.nft+0n~n#lnl#ntL0_ _ _~0Y...t
UUUUTIULJuuliuu
(iVl.L ..

(f) { (ii~1fU1JlIUl

_oTto

- - t - - - - ! t - . - - - - +100 V
••

J(i)~
()
g \(ii) rrrnrrrrY

•

+ counter O.
+ counter I.
Halver + counter 2.

(a) Halve,

.LIt} Halver
(~

Fig. 36'

+ count"" 3.
(,) Halver + counter 4 .
(f) HaJvcr, phase 2 (}fa)'

(d) Halver

(6) Staticisor triuer pips.

Fig. 37.-Circuit of stage "of Y-shift generator.

L-/3
'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 wavefonDS ell must be changed from 0 volts to beyond cut-off of
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
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.
part

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 departure. It is stated ill the -paper that there
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
oby 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· 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
only the two states. the excavated
is a 1 or a 0 there, and there
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 cathoderay 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, ,

were

••

arc

•

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
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 complexity 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

,lor.

.... L-J3

lJSB Wl'I1I BINARY-DIGITAL

•

D~JON

of a laraar project, while simpler and apparently much more '0· S mm/microsec and SOO such elements were stored on 20 anl
elegant solutions, such as the Haeft" tube. are still in the early or the available l00cm 2 of the storage-screen area.]
stqes of d e v e J o p m c o t . ,
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
giving a storage capacity
comparable to' that of many highly-specialized storage tubes,
circuits to the stora(le tube?
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 fundathat 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-modusystem 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
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 partime. 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 JW..B1.JRN: ~'S"YS1ZM FOR USB WD1I BlNARY-DIGITAL COMPU11NG

siana1/noise ratio. In the ~ of the men:ury-delay line type
it acems that the output puIIe may poIIeII qualitiel-«lcb u an
accurately controUed .wid~wbicb enable it to be distinauilhed,
fiom noise and tbemore improve the' sipaJ/noiJe diIcrimiDation. The cathode-ray tube storap systems delcribed provide
a rather odd-ibaped puJse,and it aecms that not much cin:uit
dilcriminatioD from noile, other'thaD that liven by the time at
whidl the pulse occurs, can be obCaiDed.Whether dle "antici.,.tory puIIe." or the "weD aDd weI1..fi11ina" type deiCribed by the
authors. is u.d, it eema ,that some importance must au.dl to
the liPaIInoile ratio, as it may determiDe the ultimate accuncy
whicb the computor can adlieve with any 8iwn Iia 01 problem.
Mr. D. M. MKKa,: Is anytbina known 01 the iDftuence of

~OIINES: DISCVSSION

temperann on the shape and penisteace 0( the potential well?
Althouah anaIope computation is not Itricdy within the terms
of the paper, I should like to mention u.t "" bave been experimeotina ad' a store for anaIoaue information, using a modification
Of the priDcipie delcribed. Briefty. a trail of char8e is depoIited
on a catbodo-ray ICI'een by a '-writing" spot. It is subiequeody
scanned by a raster, and the pulaes. detected in the nwmer die
authors have deacribed, are used in the obvious way to reproduce
the written waveform via a flip-ftop or a strobe circuit. With
this, anaqement it is perhaps more important than with the
dilital method to reach the limits of definition, and it would be
of interest to know what.relevant cft'ect. if uy, is produced' by
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
previous aamnina could 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
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 continuouslyevacuated 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 difficult 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(-continuous 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 f t 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, communicated 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 computen. 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.

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