Reconstruction of the Atanasoff-Berry Computer

** **

**John
Gustafson**

** **

** **

**Abstract**

The Atanasoff-Berry
Computer (ABC) introduced electronic binary logic in the late 1930s. It was
also the first to use dynamically refreshed capacitors for storage, as in
current RAM. Perhaps most astonishing is that it was *parallel,* supporting up to 30
simultaneous operations. Yet, it had far fewer parts than the serial computers
that followed it in the 1940s. Atanasoff and Berry completed the computer by
1942, but it was later dismantled. Only a few parts of the original computer
remain. In 1994, a team of engineers, scientists, and students at Iowa State
University/Ames Laboratory began rebuilding the ABC. We demonstrated the
functioning replica on October 8, 1997.

In this paper, I describe the computer in modern computer architectural terms to facilitate technology comparison. While patent applications, purchase orders, and photographs gave much information for the reconstruction, a number of mysteries about the computer were solved only as a result of the effort to reproduce it. The answers to those mysteries are presented here for the first time.

**1.
****AtanasoffÕs Motivation**

John Atanasoff was a
physicist by training, whose interests included molecular spectra and
crystallography. As a graduate student, he often found it necessary to solve
systems of linear equations by hand, and as a professor he had advisees
similarly engaged in the arduous process. He noted:

Since an expert [human] computer takes
about eight hours to solve a full set of eight equations in eight unknowns, k
is about 1/64. To solve twenty equations in twenty unknowns should thus require
125 hoursÉ The solution of general systems of linear equations with a number of
unknowns greater than ten is not often attempted.

*ÑComputing Machine for the Solution
of large Systems of Linear Algebraic Equations*

J.
Atanasoff*,* *1940*

Alt made a strikingly
similar eight years later [6]:

É13 equations, solved as a two-computer
problem, require about 8 hours of computing time. The time required for systems
of higher order varies approximately as the cube of the order. This puts a
practical limitation on the size of systems to be solvedÉ It is believed that
this will limit the process used, even if used iteratively, to about 20 or 30
unknowns.

*ÑA Bell Telephone Laboratories
Computing Machine*

F.
Alt*,* *1948*

In the evolution of
automatic computing, solving a system of linear equations was the original
ÒGrand Challenge.Ó Trigonometric functions and logarithms could be tabled, and
mechanical desktop calculators such as the 10-decimal Marchant could handle
short sequences of + Ð × Ö operations. Gaussian elimination had order *N*^{3}
operations for *N *unknowns, however, and this made manual methods unscalable. Atanasoff
listed his target applications [6], which look much like the typical workload
at a modern supercomputer center:

Multiple correlation

Curve fitting

Method of least squares

Vibration problems including the
vibrational Raman effect

Electrical circuit analysis

Analysis of elastic structures

Approximate solution of many problems
of elasticity

Approximate solution of problems of
quantum mechanics

Perturbation theories of mechanics,
astronomy, and the quantum theory

Atanasoff struggled for years to find a physical way to perform arithmetic that was digital instead of analog. He appears to have been the first to draw the distinction between the two, and to coin the term ÒcomputerÓ for a mechanical device. He thought about parallel processing much the way we do now, in that he considered connecting 30 commodity devices (mechanical Monroe calculators) to attain the necessary speed [1]. He discarded this approach as clumsy and error-prone. In late 1937 [5], he suddenly made the mental leap that provided him with what he was seeking while at a roadhouse near the Mississippi River. He jotted four principles [2] on a napkin, paraphrased here:

Electricity and electronics, not
mechanical methods

Binary numbers internally

Separate memory made with capacitors,
refreshed to maintain 0 or 1 state

Direct 0-1 logic operations, not
enumeration

On the other side of
the world, the designs of Konrad Zuse were independently paralleling those of
Atanasoff, but the Zuse designs were mechanical or relay-based [7]. While the
Zuse automatons were less advanced than the ABC in switching and storage
technology, they were far ahead of their time in having full floating point
arithmetic and a real instruction set.

By 1940, Atanasoff and
graduate student Clifford Berry had taken the above ideas to practice. I will
present details of the design, including features not previously explained in
the literature on the ABC [1, 2, 4, 5, 6].

**2. Block
Diagram**

Figure 1 shows an overview of the ABC. It uses terminology more like that for modern computers than like that of the original documentation. Terms like Òkeyboard abacusÓ have little meaning for present-day computer engineers.

* *

Because the
add-subtract modules could be used for base conversion (both directions) as
well as vector addition and subtraction, the total vacuum tube count was very
low: about 300 for the entire machine. Much of this economy is the result of
operating on only one bit of each number at a time, keeping the carry/borrow
bit in a capacitor for use in the next cycle. The 60 Hz line power served as
the system clock; one 50-bit number could be added or subtracted in 5/6 of a
second, with 1/6 of a second idle time.

The separation of memory from processing is one we now take for granted. On analog computers, there is no such separation. Atanasoff and Zuse independently made the same profound breakthrough in realizing the need for separate Òmemory,Ó as Atanasoff anthropomorphically called it. One of the few news releases of the Iowa State College (now Iowa State University) about the ABC used the headline, ÒMACHINE ÔREMEMBERSÕ.Ó

**3. Physical
Design**

The ABC is much smaller than the other early computers. The original dimensions were 1.5 m long, 0.91 m high, and 0.91 m wide. The seemingly minor decision about the width had much to do with the eventual destruction of the original device.

It was constructed in
the basement of the physics building at ISU, which at the time was an open area
interrupted only by support pillars. The basement was later finished with
poured concrete walls and standard doors; the standard door width is 0.84 m.
Hence, the computer was boxed in. After Atanasoff left ISU for Maryland, the
ABC was seen only as an orphaned device taking up otherwise useful space. Since
its frame was welded angle iron, the only way to remove it from the room was to
cut it apart with a hacksaw. I feel we have most of the answer to the question:
*Why was the ABC destroyed?* The answer is that it was 0.07 m too wide to
go through the door. In reconstructing the ABC, we made one practical
modification: we narrowed the frame enough so we would be able to go through a
standard door.

Figure 2 shows the
reconstructed ABC, using a camera angle similar to that of the historical
pictures of the original.

The weight of the
machine is about 750 pounds. It rolls on four heavy-duty casters, with the
weight and maneuverability of an upright piano. Like a piano, the ABC must be
ÒtunedÓ after moving to make sure that the timings of brush-triggered events
are still within tolerance. The remarkable thing, of course, is that any such
antique computer would be so portable. ABC successors such as the ENIAC and the
Mark I were notorious for filling rooms with bulky, heavy equipment. The ABC replica
has logged thousands of miles in its tours around the country, using a
protective crate and a truck specialized for moving sensitive scientific
equipment, and it remains functional.

We wondered about the
power consumption of the system, but have found that the total power drawn does
not exceed 1000 W. The heat generated by the tubes is barely perceptible if one
stands near the computer. There is no need for fan-driven cooling; what heat is
generated disappears by convection in the open design.

The ABC uses ordinary
U.S. line power, 117 VAC, 60 Hz. It was not designed with safety in mind; the
two main bus voltages are +120 V and Ð120 V, and in many places on the computer
large, unshielded surfaces at these voltages are separated from ground by a few
centimeters. With protective covers removed, the rotating memory drums could
easily snag loose clothing. We do not expect to operate the computer on a
routine demonstration basis, but to rely on videotapes and simulations of its
operation.

The physical design is
true to that of the original, with the exception of the slightly narrower width
and slightly more modern wire (plastic coated instead of cloth coated, coaxial
shielding instead of twisted pairs). The contact brushes are the same IBM part
used in 1939. The phenolic resin cylinders that hold the memory appear to be
the same stock as used by Atanasoff.

The total amount of
wire in the ABC is about 1600 m, and almost all connections are soldered. The
manual effort required for the wiring (and correction of wiring errors) was
probably the single largest part of the cost of the reconstruction itself. We
discovered an advantage of the originalÕs cloth-covered wire when we found that
the soldering irons had melted some of the replica wireÕs plastic sheathing enough
to cause short circuits in shielded cables.

**4. Finding
1939 Vintage Parts**

People often ask us,
ÒWhere did you get the vacuum tubes? WerenÕt they difficult to find?Ó Several
suppliers stock vacuum tubes of the correct type. An Army-Navy warehouse in
California supplied us with enough tubes for the entire ABC plus a few spares.
About half the tubes tested were gassy, but the remainder worked; most of those
that worked were still within design specifications. Finding vacuum tubes was
by no means our biggest challenge.

It was much more
difficult to find a proper synchronous motor to drive the rotating drums.
Modern synchronous AC motors can synchronize on the positive *or* the negative part of
the AC power cycle; in 1939, they were wound to synchronize on only the
positive part. This does not affect any of the computational logic, but it does
affect the base-2 card writer and base-2 card reader. Cards written while
synchronized to one phase of the motor will not read properly if the machine
becomes synchronized to the opposite phase (as can happen whenever the machine
is turned off and back on).

In building
add-subtract modules, we found the circuits very demanding of precise resistor
values. We have evidence that Berry hand-selected resistors from bins until he
found ones that worked, and we attempted the same tactic. In measuring a
collection of ±10% resistors, we discovered the following distribution about
the nominal value:

* *

Apparently, the
manufacturer had already segregated the resistors close to nominal value.
Hence, we found it necessary to use 1% tolerance resistors.

**5. Arithmetic
and Rounding Error**

The ABC arithmetic is
50-bit binary, 2Õs complement integer arithmetic. There are no tests for overflow.
There is also no rounding when it divides numbers by two via shifting. While
this may initially seem to pull values toward zero with every operation, closer
examination shows that the Gaussian elimination process causes the data to
alternate from positive to negative values, and thus the truncation of bits is
balanced on the average. After order *N *iterations of the subtract-shift
process, the values will be off by about Ã*N* bits in the least
significant place.

The simple examples in
BerryÕs thesis describing the use of the ABC use linear equations with integer
coefficients, avoiding discussion of roundoff error. Now that the
reconstruction has allowed us to experiment with the computer, it is obvious
that Atanasoff and Berry intended to scale all input values so they would
occupy the most significant bits in the 50-bit words. The Ã*N* bits of error in the
least significant place would be negligible for well-posed problems. With the
exception of circuit analysis, the physical applications Atanasoff had in mind
tend to produce positive definite matrices for which the ABC could easily
generate answers correct to ten or more decimals accuracy.

**6. A
Stumbling Block: The ABC Mass Storage Scheme**

Atanasoff and Berry
knew they would need to record intermediate results somehow. The
refreshed-memory storage was only sufficient to hold two rows of the system of
equations (up to 29 variable coefficients plus the right-hand constant
coefficient). As rows are altered by the Gaussian elimination scheme, they
would have to be stored and reloaded later.

Reading the
intermediate answers manually by conversion to decimal was out of the question.
It could take up to two minutes to convert each 50-bit binary number to a
15-decimal number on the odometer readout, which also had the inconvenient side
effect of destroying the original 50-bit number.

A mechanical cardpunch
was considered, but would have brought in all the usual disadvantages of
mechanical computation that Atanasoff was seeking to eliminate. He wanted an
electronic solution. (Magnetic storage did not evolve until after World War
II.)

The solution he and
Berry came up with was to use high-voltage arcs to burn holes in paper; a hole
for a Ò1Ó and no hole for a Ò0.Ó Berry refers to the paper as Òdielectric
material.Ó It appears that paper was the only material ever used. The thyratron
tubes visible on the left side of the ABC provided the high-voltage pulse to
create the arcs. Reading the cards was done by passing the card between
electrodes at a lower voltage than that used to burn the card, and with blunt
electrodes instead of pointed ones to allow for small differences in alignment
between reading and writing. The idea is that the arc will form in the card
reader if there is a hole in the card, but the dielectric strength of the paper
will prevent this if there is no hole.

Note that there are at
least five variables to adjust for this method to work:

1) The voltage used to
write

2) The voltage used to
read

3) The thickness of
the paper

4) The spacing of the
electrodes used to write

5) The spacing of the
electrodes used to read.

From telephone
discussions with Clifford BerryÕs widow, we learned that Berry found the
optimum paper to be Strathmore No. 2. This paper is no longer manufactured, but
we know it was thicker than ordinary bond paper and not as thick as IBM card
stock. A too-thin paper would buckle in the mechanism and would not prevent
arbitrary arcs in the reading of the card; a too-thick paper might prevent arcs
in the writing of the card, or snag on the electrodes. Unlike the rest of the
ABC, this technology was not prescientÉ unless viewed as a precursor to paper
tape punch or magnetic tape recording.

BerryÕs M.S. thesis
was to find a combination of these competing design variables that works. He
found it. The write voltage was 3,000 V, and the read voltage is 2,000 V. With
it, the ABC is able to record the entire contents of one memory drum (1500
bits) in one second. It would be many years before there was another method
capable of this I/O rate. The scratch paper cards were about 12 cm by 18 cm and
were loaded individually. As they ejected from the mechanism, they were
apparently caught by hand; there is no record of any kind of tray.

Burks [2] cite the
reliability of the arcing scheme as roughly one error in every 10^{4}
or 10^{5} bits. This is high, but probably not high enough for the
solution of 29 equations in 29 unknowns. The likelihood of a one-bit error
increases rapidly beyond about five equations in five unknowns, and this may be
the source of the debate, ÒDid the Atanasoff-Berry Computer ever work?Ó From
hands-on experience, we can now give the answer: yes, but reliability problems
prevented it from solving systems large enough to fill its memory. It was still
much faster and more reliable than hand calculation, which is what Atanasoff
had hoped to achieve.

**7. The ABC
ÒInstruction SetÓ**

The operator invokes
ÒinstructionsÓ via the buttons and switches on the control panel. A *vector* is a set of the 30
numbers in either memory drum. (The vector in memory 1 is called CA in earlier
descriptions of the ABC, and the vector in memory 2 is called KA.) A *short
vector*
is five numbers, aligned to end on a multiple of 5 within the vector; a decimal
input card held one short vector, whereas the binary scratch cards held an
entire vector. The possible instructions, with approximate execution times, are
as follows:

1 s Set
short vector to coefficients 1 to 5.

1 s Set
short vector to coefficients 6 to 10.

1 s Set
short vector to coefficients 11 to 15.

1 s Set short vector to coefficients 16
to 20.

1 s Set
short vector to coefficients 21 to 25.

1 s Set
short vector to coefficients 26 to 30.

1 s Vector
clear memory 1.

1 s Vector
copy memory 1 to memory 2.

16 s Read a short
vector from the base-10 card reader into part of the memory 1 vector,
converting to binary using table look-up and the add-subtract modules.

1 s Read
a short vector from the base-2 card reader into part of the memory 1 vector.

1 s Read
a short vector from the base-2 card reader into part of the memory 2 vector.

1 s Select
a coefficient in memory 1 (for elimination or decimal output).

100 s Add
or subtract (chosen automatically) one row from another to eliminate the
leading bit of the chosen coefficient, shifting right when successful and
stopping when the chosen coefficient is zero.

100 s Write
a value to the decimal readout, using the lookup tables and add-subtract
modules to convert the base-2 value to base-10.

The timings of more
than 1 second are data-dependent, and the values given represent averages for
15-decimal numbers. By using small integers instead of the full dynamic range,
the time for those long operations drops by an order of magnitude.

A striking omission in
the design of the ABC is the concept of *addressing*. Binary data is not
used anywhere to select data locations. The operator performed the selection,
which is why the design has so many sizes that are not powers of two (such as
5, 30, 50, 1500).

**8. Base-10
Output**

Descriptions were frustratingly
sketchy when describing where the answers finally appeared in human-readable
form. We knew that Berry had attempted to use a car odometer to record the
output, but eventually custom-made what he needed. The black-and-white
photographs of the machine did not reveal anything obviously intended for the
output, and we had to solve this mystery before reconstruction could begin.

The man who took those
photographs was also the man who did most of the wiring of the original ABC:
Dr. Robert Mather. Mather, a physicist living in Oakland, California, is
perhaps the only person still living that saw the ABC in operation. (Atanasoff
was alive when the reconstruction project began, but had suffered several
strokes and was unable to communicate with us). We contacted Mather, who
pointed out the cylinder next to the base-10 card reader in the photograph, and
all became clear. The same mechanism that moved the card reader could be used
to move a solenoid past odometer-type wheels, poking them by one decimal every time
a value on the drum with the conversion table subtracted that decimal. Unlike a
car odometer, there is no ÒcarryÓ when a wheel passes 9; the wheels are
independent. The display is small, since it has the same spacing as columns on
an IBM punch card.

Because the algorithm
alternates between adding and subtracting as the solenoid moves across columns
of the number, the wheels are numbered in alternating forward and reverse
order. This simplifies the mechanical aspects of the conversion, since the solenoid
always moves the same way but the electronics change state.

One does not find
clear answers to some questions in the literature on the ABC. I will attempt to
answer those now, based on our experience with the replica and the additional
sources of information we found in our quest for details about the original.

**9. Exactly
When Was It Completed?**

Unlike an invention
like the Wright BrothersÕ airplane, we do not have a precise date in history
for the first successful electronic computation. There does not seem to be a
precise date when one can say the ABC worked for the first time. The binary
logic certainly was working by the summer of 1940, but the base-2 scratch
storage method described above became reliable enough to use as a gradual
process and not a dramatic one. By the time World War II had taken everyone
away from the project in June 1942, the ABC was in the state that we have
reproduced, and that reproduction is a working computer.

Had the war not
interfered, Atanasoff was planning to make the instruction sequencing automatic
instead of entered manually from the control panel, and to make the computer
more general-purpose. With the exception of ZuseÕs paper-tape mechanism for
instruction sequences, stored instruction sequencing had to wait until the late
1940s.

**10. Was the
ABC Electronic or Electromechanical?**

The
fractional-horsepower motor and gear trains suggest that the ABC was an
electromechanical computer and not an electronic one. This is not the case. The
mechanical function was similar to the motor that turns the hard disk or CD-ROM
drive inside a modern computer; the gears and mechanical parts were not used
for computing or to record data in any way.

A small number of
relays were used, but only for control. They more closely resemble the on-off
switch on a modern PC than the gate elements of the Zuse Z3.

Modern electronic
computers have many moving parts in the input keyboards and output printers,
and so did the ABC. It is true that the *clocking* of the system was
mechanical and not electronic. With an oscillatory circuit used to set the
system clock instead of a rotating cylinder making contact with brushes, the
ABC logic could have been made ten thousand times faster. Note, however, that
this would have been a gross mismatch to the I/O limitations of the system.
Even the later ENIAC, which used electronic clocking, experienced its
bottleneck in the punch card input and output.

The ABC was fully
electronic in its calculation and in its storage of data. For that reason, I
argue that its mechanical aspects are no different from those of any modern
computer; a motor to rotate the storage medium, and mechanical switches for the
human interface.

**11. Was the
ABC Ever Actually Used?**

Some have claimed that
no one ever used the original ABC for production computing. We have found
evidence to the contrary. The first three applications listed by Atanasoff are
all statistical, and Atanasoff collaborated with the well-known applied
statistician Snedecor at ISU. Publicity that resulted from our reconstruction
effort led Clara Smith, a secretary in the Mathematics Department now living in
rural Iowa, to contact us. She said one of her tasks was to hand-verify
solutions to problems that Snedecor was sending to Atanasoff. It appears
Snedecor sent a steady stream of small linear systems to the ABC for solution,
and it would have been very well suited to regression, least squares,
curve-fitting problems. Clara Smith verified some of the results for Snedecor
to establish his confidence that the ABC was producing correct answers.

Robert Mather also
says the original machine solved problems up to size five, but more typically
size three during testing and debugging. The experience we have had with the
replica makes this recollection very plausible. Five is the size of a Òshort
vectorÓ that fits on one input card, and does not require any switches to be
changed on the short vector location. It also involved about 3 × 10^{4} bits to
be sent through the base-2 mass storage system, which is about where the
reliability of that system becomes limiting. A linear system size of three is
very useful in testing and debugging, since one can solve a 2 by 2 system plus
right-hand-side vector without any use of scratch storage. Since we have done
nothing to improve on the technology of the original, I feel we have settled
the question of whether the original ABC was ever operational: It was.
Moreover, it was probably used to solve real statistical problems.

**12. How fast
was the ABC?**

As in all computer
performance measurement, it is better to take into account the time to solve an
entire problem and not excerpt the time to do a single operation as a measure
of speed. The latter is usually much more flattering, but seldom reflects true
performance. For example, one could cite the fact that a 30-element vector
addition on the ABC takes only one second, implying 30 arithmetic operations
per second. Perhaps this is the Òpeak performanceÓ rating for the ABC. I
instead consider Òsustained performance.Ó To measure that, there is no
substitute for a working replica.

Because of the
parallelism in the architecture, the sustained performance is maximized if all
30 add-subtract units are used; that is, if one solves a system of 29 equations
in 29 unknowns. Burks has estimated that this would take about 25 hours,
including human operator time [2]. With a LINPACK-type operation count of ^{2}Ú3*N*^{3} + 2*N*^{2}, the
Gaussian elimination of a system of size 29 requires about 18,000 operations.
This implies 0.2 operations per second. Because the ABC had parallelism greater
than *N*, the time complexity grows as *N*^{2} and not *N*^{3}.

I have noted that the ABC probably never was used for such a large system because of the very high reliability requirements for the scratch storage. We can look at the other extreme, two equations in two unknowns. The usual floating-point operation count for a 2 by 2 system (counting reciprocation as three operations) is 19. Our experience is that such a problem can be solved in about five minutes, somewhat less than the estimate in the BurksÕ book. This implies 0.06 operations per second. The 2 by 2 system need not involve scratch storage, which saves time beyond what would expect from problem scaling.

**13. How
ÒSpecial-PurposeÓ was the ABC?**

Some refer to the ABC
as a Òspecial-purposeÓ computer, perhaps to diminish its place in computer
history. ÒSpecial-purposeÓ and Ògeneral-purposeÓ are not scientifically defined
adjectives. Most computers are designed with a certain range of applications in
mind, and the list that Atanasoff mentions above is broad. We already know that
the ABC did not have an automatic instruction stream like the Harvard Mark I;
its only capacity for branching was in testing zero crossings and zero results
during elimination. It relied on the human operator to deliver commands and
make decisions about what to do next.

After the ABC
reconstruction began to be operational, I realized that the ABC could in fact
be employed the way one would use a pocket calculator, and that it could be
ÒprogrammedÓ in a sense by the choice of matrix coefficient data. To see this,
consider what happens when one solves the system

*ax* + *by* = *u*

*cx* + *dy* = *v*

The result of one
application of the ABC row-elimination step results in

*ax* + *by* = *u*

0 + (*d* Ð *bc*/*a*)*y* = *v *Ð *uc*/*a*)

The quantity (*d *Ð *bc* / *a*) is easily read out
on the decimal display. Quantities *u* and *v* need not even be entered. If we want
to obtain the four basic operations + Ð × Ö, then

*b* = Ð1, *a* = +1 gives *c* + *d*.

*b* = +1, *a* = +1 gives *d* Ð *c*.

*d* = 0, *a* = Ð1 gives *b* × *c*.

*d* = 0, *c* = Ð1 gives *b* Ö *a*.

Although this may seem
clumsy, it was certainly easier and less error-prone than doing 15-decimal
arithmetic by hand.

**14.
Perspective: Computers Now and Computers Then**

The ABC illustrates
two remarkable things about the history of computers: First, that MooreÕs law
seems to work if extrapolated all the way to 1939, and second, that a
surprising number of things have *not* changed much from the ABC.

MooreÕs law was first
posited in 1970, using only three data points. It primarily applied to chip
density, and by implication the cost per bitÉ but because speed tends to scale
linearly with memory, it has been found to be a good guideline for processor
speed as well: *Performance doubles every 18 months*. So if we extrapolate
back to 1942 from say, late 1996, we should have doubled performance about 36
times. 2^{36 }is about 70 billion (American system, billion = 10^{9}).
Are current supercomputers 70 billion times more capacious and faster than the
ABC? Does MooreÕs law hold even before the invention of integrated circuits?

The ABC had 0.3
kilobytes of main storage. The Intel Teraflops computer delivered to Sandia
National Laboratories last year now has 0.3 terabytes of main memory and a
terabyte of disk storage. It isnÕt clear which one we should use, because the
ABC memory used refreshed capacitors like DRAM yet spun mechanically like a
disk. The speed of the ABC was, translated to modern terms, about 0.06 ÒFLOPSÓ
where we politely ignore the lack of exponent management in the ABC and look at
the 50-bit precision as similar to a modern 52-bit IEEE mantissa. The Intel
Teraflops computer, true to its name, has demonstrated a trillion FLOPS with
that precision, and running the same application. That represents a factor of
about 20 trillion.

With this improved
baseline, we can recalibrate MooreÕs lawÉ but it doesnÕt need much
modification. It looks like DRAM technology doubles every 20 months, and processor
speed doubles every 28 months. ItÕs a little like recalculating the Hubble
Constant when a telescope finds another more ancient and more distant quasar.

**15. Cost**

If the reader will
forgive my use of American units, someone once noted that computers cost about
$400 per poundÉ give or take $100. This amusing statistic is surprisingly good
at predicting the cost of everything from a pocket calculator (0.1 pound, $40)
to a Cray vector mainframe (30,000 pounds including motor-generators,
$12,000,000). While weÕd like to think that the cost of a computer stems from
its intellectual content and not its mass, the heuristic seems to work. The ABC
weighs 750 pounds, and it cost about $300,000 to reconstruct. This fits the
$400/pound estimator despite the use of vacuum tube technology. This ABC price
includes the engineering labor cost; some quoted prices for the original ABC
list $5000, and include only the parts in 1939 dollars. If one adjusts for
inflation and estimates the cost of Atanasoff, Berry, and the several students
that helped with the original, the cost of the reconstruction is very close to
the price of the original.

**16. Summary**

Scientific computer
architectures have long been designed with linear algebra in mind. The vector
computers of the late 1970s and early 1980s (CRAY-1, CYBER 205, etc.) and array
processors of the same era were strongly optimized for the kernel operations of
matrix factoring and matrix multiplication. The ABC was the first linear
algebra computer, and its 1940 performance is very close to what MooreÕs law
predicts. World War II prevented its innovations from being publicized and
credited to Atanasoff and Berry via patents or published papers. However, the
ideas of fully electronic digital logic and dynamic refresh capacitor storage
were communicated to other early designers and were thereby added to the body
of knowledge of computer design.

**Acknowledgments**

The reconstruction of the ABC was driven initially by two men: Delwyn Bluhm, Manager of Engineering Services at Ames Laboratory, and George Strawn, former director of the Iowa State University Computation Center. They obtained initial funding from Charles Durham, a successful executive who had been a student of John Atanasoff. Without the enthusiasm and vision of Bluhm and Strawn, the ABC reconstruction would not have happened. Engineers Gary Sleege, Dave Burlingmair, John Erickson, and many others worked long and hard to reproduce what Atanasoff and Berry had created over 50 years earlier. The entire project was privately funded; no government money was used.

The person who took
the replica from a mere look alike to a functioning computer was Charles Shorb,
a dedicated graduate student and as close to a modern-day Clifford Berry as one
could ask for. Mr. Shorb had worked on the Intel Teraflops computer just prior
to his work finishing the ABC, so he went from the worldÕs fastest computer to
the worldÕs slowest one (a ratio of about 10^{13}:1). When the press
release went out from Intel that its parallel processor had demonstrated over a
trillion operations per second, the problem that it solved was one Atanasoff
would have appreciated had he lived to see it: It solved a linear system of
125,000 equations in 125,000 unknowns.

**References**

A web site with
information about the ABC and the reconstruction effort can be found at http://www.scl.ameslab.gov/ABC.

[1] J. V. Atanasoff, ÒAdvent of
Electronic Digital Computing,Ó *Annals of the History of Computing*, Volume 6, Number 3, July
1984.

[2] A. R. and A. W. Burks, *The
First Electronic Computer: The Atanasoff Story*, University of
Michigan Press, Ann Arbor, 1989.

[3] J. L. Gustafson, ÒFirst
Electronic Digital Calculating Machine Forerunner to CornellÕs FPS-164/MAX,Ó *Forefronts*, Cornell University
Theory Center, October 1985.

[4] A. R. Mackintosh, ÒDr.
AtanasoffÕs Computer,Ó *Scientific American*, August 1988.

[5] C. R. Mollenhoff, *Atanasoff:
Forgotten Father of the Computer*, Iowa State University Press, Ames, 1988.

[6] B. Randell, *The Origins of
Digital Computers*, First Edition, Springer-Verlag, New York, 1973.

[7] R. Rojas, ÒSixty Years of Computation Ñ The Machines of Konrad Zuse,Ó Preprint SC 96Ð9, Konrad-Zuse-Zentrum fŸr Informationstechnik Berlin, Heilbronner Str. 10, D-10711 Berlin-Wilmersdorf, March 1996.

__________

**PROF. JOHN
GUSTAFSON **is a Computational Scientist at Ames Laboratory in Ames, Iowa,
where he is working on various issues in high-performance computing. He has won
three R&D 100 awards for work on parallel computing and scalable computer
benchmark methods, and both the inaugural Gordon Bell Award and the Karp
Challenge for pioneering research using a 1024-processor hypercube. Dr.
Gustafson received his B.S. degree with honors from Caltech and M.S. and Ph.D.
degrees from Iowa State, all in Applied Mathematics. Before joining Ames
Laboratory, he was a software engineer for the Jet Propulsion Laboratory in
Pasadena, Product Development Manager for Floating Point Systems, Staff
Scientist at nCUBE, and Member of the Technical Staff at Sandia National
Laboratories. He is a member of IEEE and ACM.