Analog/Hybrid — What It Was, What It Is, What It May Be
Analog/hybrid-What it was, what it is, what it may be
by ARTHUR 1. RUBIN
Electronic Associates, Inc.
Princeton, New Jersey
THE ZEROTH GENERATION
for granted. Furthermore, an arbitrary function generator was also not shown. Apparently, that device, which
is necessary to make analog computation capable of
solving any problem, was developed later or was
considered an oddball, along with the comparator
(which is really represented by the dry friction element,
provided that the output of the dry· friction element is
Introduction
The history of the analog computer goes back to
antiquity, where tax maps were first reported being used
for assessments and surveying. However, I shall confine
this paper to the analog computer as it evolved from
World War II to the present time. For those interested
in the history of the analog computer, from antiquity to
World War II, I refer the reader to an excellent
introductory article by J. Roedel, Reference 1. The
"Palimpsest" in which Roedel's history of the analog
computing art is included is in itself an excellent history
of analog computers in the early days d~ting from
World War II to about 1954. From page 4 of the
Palimpsest, I would like to show a diagram of computing
devices as visualized by George Philbrick for an article
in Industrial Laboratories in lVlay, 1952. Of interest to
us in this diagram on the analog side, is the separation,
at the bottom, between fast and slow analog which I will
discuss shortly. We will'also note the presence of hybrid
at the very top, and this article was written in 1952! Of
course, l\1r. Philbrick's "hybrid" was reserved for the
use of the analog computer first to obtain a ball-park
idea of a solution, then followed by a separate digital
solution to obtain a more accurate answer to the same
problem. I am certain that very few people thought of
this as being hybrid computation at the time. However,
consider this definition in the light of later work reported
by Mark Connelly (Reference 2) in his use of a
"skeleton" representation of a problem on the analog in
conjunction with a more accurate representation of the
problem on the digital.
It is interesting to observe the basic operations as
defined by Roedel in Reference 1. This is shown in
Figure 2. Note that the early practitioners of the
analog art considered differentiation to be a basic linear
element for the fast speed computers and did not show
potentiometers, since the latter must have been taken
Figure I-Structure of computing devices as visualized in 1952
641
642
Fall Joint Computer Conference, 1970
BASIC LINEAR COMPUTING ELEMENTS
SCHEMATIC DIAGRAM
MATHEMATICAL OPERATION
BLOCK DIAGRAM
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ADDITION
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I
SCALE CHANGE
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INTEGRATION
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DIFFERENTIATION
NON-LINEAR OPERATIONS
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MULTIPLIER
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ABSOLUTE VALUE
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Figure 2-Basic linear and nOll-linear analog operation and components
-o--A
e o- Kleil
Analog/Hybrid
643
Figure 3-Pullman-Standard Car Manufacturing Company's
analog computer installation
used to drive a switch or a gate connected to some other
computing element). There was a great deal of emphasis
in those days on the solution of linear differential
equations, obviously because those required the simplest
computing components. Perhaps also, because one could
Figure 5-Boeing analog computer, courtesy of
Boeing Airplane Co.
obtain check solutions to such equations with pencil and
paper, and computers, being relatively new, could not
yet be trusted.
Hardware
Figure 4-Computing equipment in a typical rack assembly
The major manufacturers during this initial period
were the Boeing Company which made the BEAC
computer, the Berkeley Scientific Computing Company
which made the EASE computer (Berkeley subsequently became part of Beckman Instruments), the
Goodyear Aircraft Company which made the GEDA,
the IDA computer with which I am not familiar at all,
the George A. Philbrick Research Company which
made the GAP /R computer, and finally, there was the
Reeves· Instrument Company which made the REAC
computer. Some pictures of these early analog computers
are shown in Figures 3 through 8. Figure 3 shows a
GAP /R installation while Figure 4 shows a close-up of
how those computing components were interconnected.
You will note an absence of a patchboard. Can you
imagine checking this one out today?
Note the telephone jack panels on the Reeves
computer and note also that the Berkeley and the
Goodyear computers are the first ones with patch
panels. These figures date from about '1952 or 1953.
EAI, which was just beginning to build analog computers, does not even show. The typical size of computers
in those days ranged from about 20 amplifiers up to 80
644
Fall Joint Computer Conference, 1970
need for such devices in the design of their own equipment, whether it was airplanes, electronic gear such as
radars, or control systems. Philbrick, on the other hand,
and possibly also the Berkeley Company, concentrated
from the very beginning on the process control
applications.
Applications
Figure 6-Goodyear GEDA computer installation, courtesy of
Goodyear Aircraft Company, Akron, Ohio
amplifiers, which was considered to be fairly large. One
manager, in fact, was proud of the fact that he could
expand his 80 amplifier installation to 160 without
requiring any additional wiring. The accuracy of the
components was of the order of one percent (and that
applied to resistors and capacitors as well as to the
electrical components). Overall solution accuracies on
what was then considered medium size non-linear
problems was of the order of five percent. One final point
of interest is that several of these manufacturers,
mainly Boeing, Goodyear, and Reeves were primarily
aerospace/defense manufacturers who saw the obvious
Figure 7-Berkeley EASE computer, courtesy of J. B. RAE,
Los Angeles
The 2nd page of the table of contents of the
Palimpsest is reproduced here in Figure 9 and shows the
wide variety of applications that were actively investigated in the early 1950's. You will note in parti~ular
the beginnings of an analytical attack on our environmental problems in the papers on the freezing and
thawing of soils as well as flood routing. The analog
equipment, especially that which did not have patch
panels was generally purchased for a particular problem
or problem type. For example, the Pullman Car
Company would buy one for solving their "transportation equipment design" problem. An aircraft manufacturer would buy a computer to study the control
system of a particular airplane. There was an almost
complete lack of user conveniences leading to the
ridiculous situation of being able to obtain a complete,
single solution to a complex set of differential equations
in 5 milliseconds, but having to wait several days, at
least, to change to another problem, due to the lack of a
patch panel and other amenities, such as a readout
system. This type of inaccessibility (to the Hnext"
Figure 8-Reeves computer installation, courtesy Reeves
Instrument Company
Analog/Hybrid
problem) has been at the root core of the ailment in the
analog field and has given the analog computer the
reputation of being "inflexible." This ailment is still
with us, albeit to a much smaller extent, and a cure is
visible on the horizon, as we shaH see later. For further
information on techniques and methods that were
expounded in the early years of analog computation, the
reader is referred to References 3, 4 and 5. This by and
large represents the first generation analog; however,
since I seem to have too many generations, as we shall
see later, I will term this the heroic age, or the zeroth
generation. This generation coexisted with the heroic
age digitals, such as the ENIAC, EDVAC, the
ORDVAC, l\1ANIAC, and the UNIVAC.
645
MODELLING of PHYSICAL PROCESSES............................................................
146
The Electro-Analogue..............................................J. M. L. Janssen and L. Ensing
147
Discontinuous Low.Frequency Del.y Line with Continuously V.ri.ble Delay
......................................................................................................J. M. L. Janssen
162
Bucket·Brigade Time Delay..............................................................G. A. Philbrick
163
Solving Process-Control Problems by Analog Computer..................................... .
............................................................................ R. J. Medkeff and H. Matthews
164
ELECTRONIC ANALOG METHODS in DETAIL..............................................
167
Precision in High.speed Electronic Differenti.1 Analyzers................................... .
..........................................
.............................. H. Bell, Jr., and V. C. Rideout 168
An.log Computer Solution of • Nonlinear Differentiai Equation ....................... .
............................................ .......................... H. G. Markey and V. C. Rideout
177
The Study of Oscill.tor Circuits by Analog Computer Methods......................... .
.................................................. H. Chang. R. C. Lathrop, and V. C. Rideout
184
A Differe~ltial.An.lyzer Study of Certain Nonlinearly Damped Servomechamsms..................................................... R. C. Caldwetl and V. C. Rideout
193
Appf~tiori of .n An.los Computer to Design Problems for Transponation
THE FIRST GENERATION
The next generation, here termed the first, more or
less coincided withthe arrival of EAI on the scene, with
its establishment of the firm need for a patch panel and
an integrated set-up and readout console as part and
parcel of the analog computer. In other words, human
factors entered into the picture, also, this generation saw
the arrival of the .01 percent component, such as resistors
and capacitors, which allowed linear problems to be solved
more accurately than the solutions could be dispJayed
on a strip chart recorder, X - Y plotter, or oscilloscope.
The credit for this shift in emphasis on more accuracy
and more user conveniences must go to the manufacturers who went against the ideas of some of the then
old line users, who kept pointing to the problems that
were being solved and observing that much of the input
data was unknown perhaps even within a factor of two
of the correct value. These old time analysts recognized
that there was no need for obtaining very accurate
solutions to such problems. However, they overlooked
the crutch available to the insecure analyst if he can get
a repeatable, accurate answer even though the model
is not exact. This analyst then has fewer questions from
his management, because when he goes back for reruns,
he gets the same old answer to compare with at the same
time, the solutions for the new set of parameter values.
Thus, he and management both think they understand
the problem.
(Aside-I learned this trick early in the game. In
order to convince my management and customers as to
the validity or correctness of a set-up to a problem, I
always went back to a "standard" solution, if a check
solution was not available. And if the standard or check
didn't repeat, then I would hopefully "tune-up" the
equipment to produce a "replica" of the check solution.
In some cases, I must confess, I may have "de-tuned"
the equipment to produce the so-called "check".)
EqUipment ...................................................... ............................................J. Roedel
199
ANALOG STUDIES of ELECTRIC POWER SYSTEM TRANSiENTS........
216
Surge and Water. Hammer Problems............................................... H. M. Paynter
217
Methods and Results from MIT Studies in Unsteady Flow ........ H. M. Paynter
224
The An.log in Governor Design ...................................................... H. M. Paynter 228
Tie Line Power" Frequency Control........
.................... H. M. Paynter
229
Electronic Computer for Resolution of Steady - St.te Stability Problems and
Panicularly for Automatic Control Studies................................... .I. Obradovic
233
How to Select Governor Parameters with Analog Computers ............................ .
...... ..... .................................... ............ E. C. Koenig and W. C. Shultz 237
COMPUTER TECHNIQUES in HyDROLOGy...................... ...........................
Flood Routing by Admittances...
..................................... H. M. Paynter
239
240
ANALOG SOLUTION of THERMAL PROBLEMS.........................
246
Freezing and Thawing of SOils .................... H. P. Aldrich. Jr., an<l H. M. Paynter
247
The Analogue Computer and Automatic Control Applications .... R. J. Bibbero 261
Process Regulation with Analogue ControL .................................. R. J. Bibbero
264
Continuous Electric Representation of Nonlinear Functions of n.Variables
.................................
... G. A. Philbrick
266
Fir .. 1 IlrilitinK PH;;
SnoolHl printinr.: 1'1'&
rhirtl printing I'Jf,O
Fourth printing 1965
Figure 9-A portion of the table of contents of the Palimpsest
Conveniences such as a digital volt meter readout of
amplifiers and all other components via push-button
selectors, servo set pots as well as experiments with
quarter-square multipliers and time division multipliers
were introduced. The second phase lasted roughly from
1955 to 1960 and saw the rise of EAI from the position
of young upstart to that of the major supplier of analog
computing equipment. While EAI was rising, the
period saw several companies such as Boeing, Goodyear,
IDA (or perhaps Mid-Century) drop out of the industry.
After these defections from the ranks of the manufacturers, the field of slow speed analogs was split amongst
EAI, Berkeley, which by this time had become merged
with Beckman, and Reeves Instruments. The high speed
analog now had two manufacturers, the old Philbrick
Co. and a newcomer to the high speed camp, the GPS
Company. This period saw the 31R and the 131R and to
lesser extent, the Reeves' C400 gain wide distribution.
646
Fall Joint Computer Conference, 1970
1958 NATIONAL SIMULATION CONFERENCE, continued
Ehlers, "Standard Simulation Circuits"
Gilbert, '"rhe Design of Position and Velocity Servos for Multiplying
1958 NATIONAL SIMIlLATION CONFERENCE
Clymer, "Operational Analog Simulation of the Viration and Flutter of
and Function Generation"
Sinker, "The Card Programmed Diode Function Gener-ator"
a Rectangular Multicellular Structure"
Shen, ''Multiplier Circuits Utilizing Squaring Property of a Triangular
Powell, "Distributed Parameter Vibration With Structural Damping and
Wave"
Noise Excitation"
Pfeiffer, "A Four Quadrant Multiplier Using Triangular Waves, Diodes,
Ladd and Wolf, "A Non-Real-Time Simulation of SAGE Tracking and BOMARC
Resistors, and Operational Amplifiers"
Guidance"
Miller and Enger, "Liquid Transfer and Storage System Simulation by Active
Element Computers"
Azgapetian, "Some .Aircraft Probl_ S1aJlated by "ean8 of Z-forms"
Boxer, ''Z-forms, and the Digital St.ulation of Dynamics"
Ehlers, ''General Purpose DC Analog Computer with Transistor Circuitry"
Pritsker, Buskirk, and Wetherbee, "Simulation to Obtain Systems Measure
of Air-Duel Environment"
Billinghurst and Single, "Extending the bandwidth of Precision Analog
Systems"
Nemerever, "A New Technique in System Perfor_nce Evaluat ion"
Gilbert, ''Linear System Approximation by Differential Analyzer Simulation
of Orthonormal Approximating Functions"
BrllllllDer, "Solutions of Convolution Integrals by Analog Computers"
Rideout, "Some Applications of a High-Speed Analog Correlator"
Bekey and Whittier, ''Generalized Integration on the Analog Computer"
Bruns, and Wilcher, '"rransistorized Relay Amplifier"
Neshyba and Coffman, "Airborne Radar-Beacon Traffic Simulator"
Munson and Rubin, Optimization by Random Search on the 'Analog Computer"
Rawdin, "A Time ~ltiplexing Technique"
Schwarm, "Computer Systems for Jet Transport Simulators"
Heffron and Bristow, "A Method for Helicopter Rotor Performance SilllUlation"
Bush and Orlando, "A Perturbation Technique for Analog Computers"
1958 NATIONAL SIMULATION CONFERENCE, continued
Morrison, "APPR-I Simulator Description"
The end of the period saw the introduction of the 231R
computer, (See Figure 13) a machine which was to see
much service in the '60s.
Meilander and Hellman, "A Technique for Absolute Measurement of Analog
Computer Capacitors"
Gerlough, "A Comparison of Techniques for Simulating the Flow of Dis-
Applications
The applications of this era (the end of the first
generation) perhaps are best described by scanning the
list of titles of papers that were presented at the 1958
Fall National Simulation Council Conference (Figure
10). From the list of titles it is clear that the aerospace/
defense industry dominated applications, but there were
a significant number of papers reporting new mathematical techniques and even applications of digital
computers to the field of simulation. New hardware
circuits such as the card programmed diode function
generator and a quarter square multiplier were first
described. Also included were descriptions of a much
later transistorized analog, a computer optimization
study by analog computers, as well as discrete event
simulation by digital computers.
crete Objects"
Figure 10-1958 National Simulation Conference
THE SECOND GENERATION
The next generation which I must here call the
second, lasted roughly from 1960 to 1965. The size of the
analog computer at the upper end was getting physically
larger and larger, which by virtue of the vacuum created
at the small end led to the design of a small desk-top
computer, which was the logical outgrowth of the
transitorization of analog components. The first transitorized computers were of the small desk-top type and
had a voltage range of plus or minus 10 volts. They
Analog/Hybrid
coexisted with their big brothers, the 100 volt vacuum
tube computer, during this period. Another hardware
innovation sa \,. the combining of heretofore separate fast
and so called slow analog into a single machine. This
occurred in both the desk-top machines as well as the
large 100 volt machines. This latter turn of events, was
brought about by the introduction and the widespread
use of quarter square multipliers, replacing the old slow
servo and time division multipliers. At the same time,
manufacturers introduced the fixed diode type of
function generator for such analytical functions as sines
and cosines of angles and exponential functions. The
above developments, in conjunction with the introduction of solid state highspeed switching made the high
speed and the low speed analog in a single computer a
practical reality.
Two new companies were formed during this period
that proved to be significant factors throughout the
'60s. These were Comcor, Inc., which subsequently
merged with Astrodata, and Applied Dynamics, Inc.,
which subsequently merged with Reliance Electric.
These companies helped to fill the partial vacuum
created by the withdrawal of GEDA from the field
during the second generation and the subsequent rise
and fall· of several other companies. During the same
period (1960 to 1965), the Reeves Instruments Company, which had been in the business of manufacturing
analog computers from the very beginning, more or less
indicated that it was finished with this activity.
The second generation equipment brought to fruition
the concept of patchable, parallel, digital logic as an
integral part of the analog computer. At the same time,
it should be noted that the first conference on the use of
combined analog and digital computers in a single
problem simultaneously, (the first conference on
essentially hybrid applications) was held in 1960,
Reference 12, which is why I chose 1960 as a key date
for the second generation.
Hybrid computation evolved along several different
paths. In one path a "stand-alone digital," was placed
next to a "stand-alone analog" with communication
between the two allowed via logic lines, control lines,
an AD (analog to digital) converter with a multiplexer,
and several D / A (digital to analog) converters. Along
another path a "logic computer" was developed by
Electronic Associates which consisted of a number of
parallel, patchable circulating (memory) delay lines,
"and" gates, "or" gates, flipflops, four bit registers,
shift registers, and one shots (mono-stables) to the point
where, if a programmer were clever enough, he could
devise and patch together his own special purpose
digital computer. The logic computer ultimately got
reduced to a reasonably small, manageable complement
of logic functions (see Figure 14) on later analog
647
Index: Volume 4
"'Ntol Comput~r 'ot~lt~en. OillUl1 Computer
Control of. W I eMM/e,.nd. •. McChH.. ..
Counter·Current CrysrlUIUlton Process,
A".'ol Simul,lion of .II. W. L God'r~.nd
It. D. ~nh.m ..
Differential Equ.tions. The OE5-', A New
0,.,1,1
'.n
'.n
Computer for Solvina. L Le'lfin....
. Apr
Dilir.' Differenli., Amlyzer.nd .ts Apphc.tion IS.
Hybrid Compuli"1 System (I~nl. TM '.r.II~,
O. A. R.eich.rdt, M. W Hoyr..nd W T LH
. Feb
Equlpotenti.! lines of. Potentill' f.eld, Plottlnl the.
w. R. Lym..
. ...................... Feb.
81
Fotly-Step Qu.ntinr. H. ~tA:s .nd C. M. C.lUwn . . Mlly
)01
26
HysteresiS, Use of tOBie.' EI~ts to Simul,te.
C W. Schulte..
. ................... JuM
164
264
104
Imperfect Differenti'tor. A Note on the Simul'tlon
of the. A. Bridgem.n .. ..................... J.n.
Muhiplier, A four-Qu.dr.m. W H. Alliston ....... ,.n.
Reticle Ev.lu.tion Studl~. A Mflhod for G~'.tin.
21
S~mple·~nd·Hold CircUli, Hllh Sentitivity,
Di~~!i~~~i.~ ~r~~r;:r~':.~u~;dtoUt ~nd
Simul~ted T~rleu Use'd In, M. O. C.mp ........ Apr.
L. T.v~rnin; . .
J.n
Hybrid Computer, MAD.l~ ... ~ Prolnm for
DiSiul Simul~hon of ~. V. C .idroot and
L T~vernjn; ..
Hybrid Compul~lion, A Discunion of I«klTYn' ..
ApptOalch 10, It E. lord lind R. A. Ne5blf
June
Hybrid C~mputins System EIetlK"flf, TM Parlillef
Dilit~r Differenti.. l An.tlyzer .. nd .1.. Apphe.. llon
~s ii, O. A. Reichilrdt, M. W. Hoyt. ~nd W T Lff . . Feb.
Hybrid Sisnil' Processor, A Pu.lleI/Sequentilll,
Stored Prolrilm,}. D. Crilndine.nd T C H ••~n . . Jan
l.suerre functions, Function GeMr.hon on
An.log Computer UsinS <d'neralized. C H Bur,in. Mlr.
Measuring Statistics from QUilntlzed Dilla, Hybrtd
Computer Techntqufl for, C. A Korn
. Apr.
Nonstahonary R.ndom Processes, Generation of,
R. E Sry.n..
. ... J.n.
Numeriul M~lhod for Simu',Ition, A N~,
M.Fcwvlef..
Mily
Pontry'gin's MilJumum Principle to Solve OMDimensiON' Oplimlz.tion Problems, With .nd
without Constraints, on iln Ite,.tive ANlol
Comp'ltt"'r, Usinl, H. L. Steinmetz
.. tUM
Pseudo-R.ndom Noi~, FJCPt"'rimt"'nls Usinl.
It L H,Impton..
Punched-C.,d Prolrammer, MACON: MAtriX
CONnector, L. /. K.mm..
223
C. C. Willem5 ................. .
'.n
APACHE. It 0 'renn.n .. nd R. N. Lin~rpf
1-42
Let's fiCe .t, It 0 'renn.n.nd It. N. linftJ.,'~t ... Apt.
226
PACTOLUS Prolr.m for S,mul.tion of Antt"'nN
Servos, U~ of th~, N. B. Kurek ............... . J~ne
16S
229
An.l08 D.tIi Procflsinl with. Hybrid Computer.
W. C. McClintock...
, ..... , ............... June
169
Anlilos Ori~nted 'nput L..n8u'It"', A Compilet with
.n, M. L. Sf~;n. /. Ros~,.nd O. S. P.tlc~f ......... Mar.
159
382
Hum.n Intefilchon In S""U Groups, Computer
Simul.tion of, J. T. Cull.horn and /. E. Cull.horn . . 'an
50
. . Apt
246
Input liIn.u.... A Compiler with
A",'08
Oriented. M L. St~in, /. Rmt"', and D. B. P..tk~t .... Mar
159
. .Mlly
332
R,Indom Proces~, Cenefiltion of Nonst.tion"y,
R. E. Sry.n..
. ... Jan.
River Kit.bmi, Flood Simul.tor for the. K Otobil.
K. Shib.ir.ni, .nd H. Kuw.t.. .
.. Feb
42
Notw eene,.tor. A Hybrid ANlol-Dilital
ps.udo·a.ndom, R. L. T. H.mpton ...
86
p.,.m~t.r Optimizer for ASTRAC II, A Hybrid
.n
Simul.lion, A New Numeric.l Method for.
M. E. Fowler ..
....... Mly
Simulation of a Chemic.l Feedt"'t System, An.lrsis
.Ind. J. C. Vogt .•............. ..... . ....... Apr
Simulation of. Spinning Rigid Body. Quaternion
P.rameters in the. E. E. L. Mirchell.nd
A. E. Roger5 ......... , ..................... JUM
State Vari.ble Techniques irr An.'08 Compuler
Programming, AppliCiltion of. /. L. Holmmond, Ir . . Mily
St.tistics from Qu.ntized D.ta. Hybrid·Computer
Techniques for Meuuring, C. A. Korn..... . ... Apr.
312
104
35
324
2S6
.n
LNrnlnl Control Systems. A Comput~r Simul.ted
On-LIM Experinwnlln. /. O. Hill, C. J. McMurtry,
.nd K S Fu ................................ ·.Feb
. .... Mlr
179
Ana'OI·0illt.l, a. A. Mitcht"'lI, Jt .............. June
199
P.rti.1 Differential <>per.tors, A New Method of
Ana'yzin. tht"' TruncAtion f"o, in the Finit~
Represent.tion Difference of, R. Vichrwveuky ... Mar.
190
'~do· ••ndom Noi~ Genero1tor, A Hybrid
390
229
ANto1,Oi1it.1. R. L T. H.mpron. , ............ Mar.
Tfilnsistors in Curr~t-Arylo. Computinl.
t. P. Kefloot. . ..................... ,..... .. May
Trunation Error in the Finite Itepresentlltion
Difference of P.rtl.' t)iff~ti.1 Oper.tors, A New
Method of Ana'yzinl the. R. Vichnfovets'y ...... . Mi:r.
119
339
190
SIMULATION
Figure ll-Index to Vol. 4 SIMULATION, June, 1965
computers and became fully integrated with the analog
computer instead of being a separate device.
The largest analog computing consoles had upwards
of 200 amplifiers in them. One example is the Applied
Dynamics 256 (Figure 15) which had 256 amplifiers.
There was a movement towards more "committed"
amplifiers such as the class 0 type quarter square
multiplier with many of the largest, most sophisticated
users trending towards the class 0 resolver as well. This
meant the computer was easier to use, but it became
more expensive.
The applications of analog during the period 19601965 are more difficult to characterize since by this time
the well known industry-wide Spring and Fall Joint
Computer Conferences, which are sponsored by AFIPS,
had replaced the old National Simulation Conferences.
To help plug the information on applications gap,
a significant event occurred during the second generation, which was the launching and the publication of the
new journal SIMULATION by Simulation Councils,
Inc., under the editorship of John McLeod. The index
of articles published in Volume 4 (June, 1965) is shown
in Figure 11, as an example of the type of applications
648
Fall Joint Computer Conference, 1970
that were being done on these bigger, better and more
powerful systems. It may be remarked in passing that
even during this second generation period, indeed
throughout the history of the analog, the analog has
been used very much as it was originally used when there
was no patchboard on the analog console. This method of
use consists of committing the analog to a single
problem, of very high priority, and tieing it up full time
doing the same job over and over and over again, as
exemplified by the.typical hardware or man-in-the-Ioop
simulator. Very often when the project that required the
simulator was completed or nowadays we would say
cancelled, there was no further use or need for the analog
computer, since no one else had been able to get at the
machine during the "fat" days. Those analysts who had
short duration, small problems, which can be considered
to be ideal candidates for the analog computer, especially
during the development or the "model" stage of the
problem, were forced to go against their own wishes to
the, by then, widely .available large, fast, digital
computer of the 7090 class. These small, repetitive,
studies went to digital not because the machine was fast,
not because the digital was cheaper, not because it was
better, not because it was more accurate, but simply
because it was available!
THE THIRD GENERATION
The third generation has shown itself to be in
existence from roughly 196,5 to the present time, 1970.
The major hardware characteristic of this generation is
the complete transitorization of the analog computer,
for both the large scale 100 volt machine and the small
scale 10 volt machine. A new scale machine evolved in
between these two extremes, called the medium scale.
A major hardware feature is the integral design of
digital logic as part and parcel of most analog consoles,
~
1962
1964
Typical Computer
231R (EAI)
recorder now compatible with accuracy and re-
continued
peatability of computer.
231RV (EAI
Electronic mode control of integrators, time-
Beckman
More useful bandwidth.
scale selection (6 decades) via push buttons,
more accurate multipliers and sinusoid generators.
Digital logic control capability - for
the first time analog has a full 10KC bandwidth
in all components, Variable breakpoint and polarity, card-programmed function generators.
This allows instant set-up of DFGs (takes only
one hour to turn around a problem). (Mostly
pot set t ings time.)
!!!!:
Typical Computer
1951
ClOO (Reeves)
1966
Ci-5000
ADI-4
analog cOlllputer - all gates (reset, hold, operate,
duction .of removable patchboard.
EAI 8800
are electronic) bandwidth up to and beyond 100 KC,
EAl 680
1954
3lR (EAJ)
20 amplifier computer, expandable to 60; more
l3lR (EAJ)
C400 (Reeves)
reliability e.timated as 60,000 hours KrBF for
_plif1ers vs. 5,000 hours measured on 231R-V.
accurate servo multipliers; integrated slaving
1956
Fully tranSistorized, more accurate, more reliable
20 amplifier computer; servo multipliers intro-
system; .01% capacitors; .01% resistors, both
C_puters can have 300-400 a ..pl1fier. in one
temperature controlled.
console.
Analog directly controllable by .... 11
digHal c_puter.
Integrated readout; human engineered for faster,
hybrid co.putation.
easier programmer use; electronic time division
Easy ... ting with digital for
Self-contained patchboard _
digHal logic (much, IlUch larger than in 23IR-V).
multipliers; mechanical digital voltmeter; tube
Card-set DFGs progr_ble from a standard IBM
diode function generators.
card.
1959
231R (EAJ)
100 amplifier computer; modular concept patchboard;
significant improvements in amplifier bandwidths
providing faster response and switching ti~es;
compressed time capability (some jobs can be run
~
Typical Computer
1968 to
ADl - Various
Digital pots for microsecond (electronic gate)
Present
EAI - Various
setup - or millisecond (reed relay setup),
as fast as 10:1 real time instead of all at real
large scale use of MDACs in hybrid interface,
time); faster potentiometer readout; electronic
software developed for autaaatic setup and
digital voltmeter; solid state diodes in function
checkout of hybrid analog computers.
Direct
generator; repetitive operation capability.
digital/analog function generator (more accurate
1962
Improved
More accurate 1/4 square multiplier; electronic
than card set diode function generator) com-
231R (EAI)
sinusoidal generator; point storage via trans is-
pletely controllable from digital computer.
tor circuit; card-set function generators; Mark 200
Figure 12-History of analog computer evolution since 1951
Analog/Hybrid
649
Figure 14-Digital expansion system by EAI (allows parallel
patchable digital logic expansion to 10 volt systems, in a
.
self-contained desk top frame
Figure 13-231R computer, courtesy Electronic Associates, Inc.
small and large, which has certainly made pure analog
computation, if we include this digital logic, more
powerful than it has ever been. Another hardware
feature is the complete flexibility of the multi-time scale
integration capability of the analog, wherein one can
have a choice of fast, slow or in-between speeds of
solution as well as the flexibility of using any integrating
capacitor as an integrator gain. The most versatile
machines have. a choice of 6 capacitors, giving the
programmer a five-decade range of integrator gains or
time scales. Examples of this class of computer are the
Applied Dynamics AD/4 (Figure 16), the Electronic
Associates, Inc. 8800 (Figure 17) .and the Comcor
Ci-5000 (Figure 18). Note the two patchboards in each,
one for digital logic, and one for analog components.
This· period also saw a more intimate ·tie-in of the
analog computer with a digital computer due to the
development of such true hybrid devices as the lVIDAC
(multiplying D/A) and the "digital attenuator" or
"digital potentiometer." So widely accepted has the
hybrid aspect of analog computation become that it
appears that close to half of the larger consoles that are
being sold at the present time are going into hybrid
systems. This in turn has led to the need, and the
development of software specifically designed to aid the
hybrid programmer and operator. The large systems
have grown larger and larger and now are truly prodigious, consisting of 300, 400, even 500 amplifiers in a
Figure 15-Applied Dynamics large scale 256 amplifier computer
650
Fall Joint Computer Conference, 1970
Figure 16-Applied Dynamics AD /4 analog computer
single console. At the low end of the scale, the 10 volt
desk-top computers have grown larger and larger until
they are no longer desk-top and now are fully grown
consoles consisting of several hundred amplifiers, as
exemplified by the EAI 680 computer shown in
Figure 19.
The solid state revolution, which only overtook
analog in the third generation has led to the concept of
the class 0 type component or "blackbox" use of the
analog components to help minimize patching and to
make it easier for the more casual user of the machine to
program, patch, and obtain solutions by himself.
Another reason for this trend is that the solid state
amplifiers are obviously less costly and more reliable
than their vacuum tube predecessors. Analog speeds of
solution which could be too fast to be absorbed by
hUrhans, or recorded by devices, even back in the early
50's, are even faster. Present day bandwidth ranges
from a minimum of 100 KHz to over 1 MHz. Some of
the other important equipment improvements are
quarter square multiplier accuracy of close to 0.01
percent and arbitrary function generation performed by
a true hybrid device, the digitally controlled function
generator (DCFG), which eliminates >spurious·· drifts,
non-repeatability;, and difficulty in setup of the old
diode function generator. These, together with the new
digital potentiometer, a good hybrid interface with good
software, and a well integrated system design, make it
theoretically possible to setup and checkout an analog
computer in a few seconcls.
Some persons have been lmown to state the opinion
that an analog computer of today is not much different
than one of 10 years ago. A reading of this paper should
dispel such a notion. To make clear the advances that
have been made in the analog field, from post W orId
War II to the present time, I have summarized in
Figure 12 the major hardware improvements by year
of general availability showing the typical computers
incorporating the named improvements. It is obvious
that these improvements have come at more frequent
intervals than analog computer generations as I have
defined them, and shows that major improvements have
come along in the analog field at an average spacing of
about 23-1 years. This interval of time is, interestingly
enough, approximately equal to the half-life of a
"generation" of analog computers. This fact might lead
to the conclusion that one generation of computers
cannot survive (or absorb) two sets of major hardware
improvements, but that the manufacturers have been
reasonably successful in extending the life of a generation
of their computers through .at least one significant
hardware evolution. Perhaps it is the ability to extend
the life of a "generation" of analog computers, because
of the nature of the organization of analog computers
(parallel building blocks) which has led to the inaccurate
observation that "analog computers of today are not
much differen.t than they were 5 or 10 years ago."
ANALOG/HYBRID TODAY
We have now come to the point in analog/hybrid
developments where not only do we have more raw
computing speed than it is possible to take full advantage of, for solutions, but we also have more speed
in terms of setup and checkout than we have customers
Figure 17-680 lOV computer with display wing
Analog/Hybrid
who understand this type of computation. Or to put it
another way, we've reached the stage in evolution where
we can get a customer on, get his answers for him, and
get him off, far faster than is justifiable based on the fact
that we have a highly serial, slow input, mainly the
input from a single man, to a very fast parallel console.
We have almost reached the stage, as a matter of fact,
where the slow recorders on the outputs from the analog
are one of the limiting output factors. We've reached
the point where we can make many, many solutions in
a very short time. In other words, we are production
oriented in terms of solution speed. At the same time,
we have retained all of our man-machine interactive
capabilities which everyone says is desirable in the
engineering use of computers, but which obviously work
against production. In fact, production capabilities are
so great that I have estimated that for every hour of
production running on our modern hybrid systems, the
amount of post run data reduction of the results by a
large fast, stand alone digital computer operating in a
batch mode would be at least two and possibly as high
as five hours depending on how much analysis is
desired, or more realistically, how much the project can
afford.
The application of hybrid equipment is still heavily
oriented toward the aerospace-defense industry where
most of the large systems are installed. The chemical
process industries have maintained some interest in
these systems over the years, but not at an increasing
rate. The education field has interest in the small and
medium size systems. Nuclear and power technology
have shown signs of increasing awareness of the
':lap ability of hybrid systems for their highly complex
Figure 18-Comcor Ci-5000 analog computer
651
Figure 19-8800 100V transitorized computer with display wing
design, control, and training studies. Other popular
applications are as an on-line testing device, such as
measuring the amount of pollutants in an automobile
engine exhaust (Reference 6); measuring the roundness
of tires
(Reference 7) in acting as an on-line predictor or
/
ad;iptor-controller for a wide variety of processes
(Reference 8), and for helping to control the quality of
s~el (Reference 9).
, So what is the hybrid/analog system of today? It is a
highly efficient fast production device when the user or
man is not allowed to intervene and interfere with its
operation. This is in direct contradiction to its other
main feature, that is, its ease of man-machine communication which almost cries out for man's intervention.
I would say that the analog/hybrid computer exhibits
schizophrenic characteristics which may explain why
not too many people understand it. It is almost
impossible for a device to be responsive to man's
intervention and at the same time to be highly productive. At leaSt not the way the hybrid systems are
configured today. It is this paradox that limits the
expansion of· the analog/hybrid field.
The analog hardware today is far more reliable than
its early beginnings. The MTBF for a transistorized
amplifier is somewhere between 30,000 hours and
60,000 hours. The high quality, chopperless amplifier, a
recent devel