Atanasoff Berry Computer
The Atanasoff-Berry Computer was the first electronic digital computer . It was built by Dr. John Vincent Atanasoff and Clifford E. Berry at Iowa State University during 1937-42. The Atanasoff-Berry Computer represented several innovations in computing, including a binary system of arithmetic, parallel processing, regenerative memory, and a separation of memory and computing functions. It is sometimes referred to by its initials, ABC. John Vincent Atanasoff was awarded the National Medal of Technology by President George H. W. Bush in a Ceremony at the White House on November 13, 1990.
The Atanasoff-Berry Computer, constructed in the basement of the Physics building at Iowa State University, took over two years to complete due to lack of funds. The prototype was first demonstrated in November of 1939. The computer weighed more than seven hundred pounds (320 kg). It contained approximately 1 mile (1.6 km) of wire, 280 dual-triode vacuum tubes, 31 thyratrons, and was about the size of a desk.
It was not a stored program machine, which distinguishes it from later, more general machines, such as the 1946 ENIAC, 1949 EDVAC, the University of Manchester designs, or Alan Turing's post-War designs at NPL and elsewhere.
The machine was, however, the first to implement three ideas that are still part of every modern computer:
- Using binary digits to represent all numbers and data
- Performing all calculations using electronics rather than wheels, ratchets, or mechanical switches
- Organizing a system in which computation and memory are separated.
In addition, the computer pioneered the use of regenerative capacitor memory, as in the DRAM still widely used today.
The memory of the Atanasoff-Berry Computer was a pair of drums, each containing 1600 capacitors that rotated on a common shaft once per second. The capacitors on each drum were organized into 32 "bands" of 50 (30 active bands and 2 spares in case a capacitor failed), giving the machine a speed of 30 additions/subtractions per second. Data was represented as 50-bit binary fixed point numbers. The electronics of the memory and arithmetic units could store and operate on 60 such numbers at a time (3000 bits).
The logic functions were fully electronic, implemented with vacuum tubes. The family of logic gates ranged from inverters to two and three input gates. The input and output levels and operating voltages were compatible between the different gates. Each gate consisted of one inverting vacuum tube amplifier, preceded by a resistor divider input network that defined the logical function.
Although the Atanasoff-Berry Computer was an important step up from earlier computing machines, it was not a stored program computer. An operator was needed to operate the control switches to set up its functions, much the way boot programs would be entered in later computers. Selection of the operation to be performed, reading, writing, converting to or from binary to decimal, or reducing a set of equations was made by front panel switches and in some cases jumpers.
There were two forms of input and output. Primary user input and output and an intermediate results output and input. The intermediate results storage allowed operation on problems too large to be handled entirely within the electronic memory.
Intermediate results were written onto paper sheets by electrostatically modifying the resistance at 1500 locations to represent 30 of the 50 bit numbers. Each sheet could be written or read in one second. The reliability of the system was limited to about 1 error in 100,000 calculations by these units, primarily attributed to lack of control of the sheets' material characteristics. In retrospect a solution could have been to add a parity bit to each number as written. This problem was not solved by the time Atanasoff left the university for war-related work.
Primary user input was via standard punched cards and output via a front panel display.
The ABC was designed for a fairly specific purpose, the solution of systems of simultaneous linear equations. It could handle systems with up to twenty-nine equations, which was large for the time. Problems of this scale were becoming common in physics, the department in which John Atanasoff worked. Basically, it could be fed two linear equations with up to twenty-nine variables and a constant term and eliminate one of the variables. This process would have to be repeated manually for each of the equations, which would result in a system of equations with one fewer variables. Then the whole process would have to be repeated to eliminate another variable.
The initial funds to start development and demonstrate the circuits involved was from the Agronomy department which was also interersted in such problems for economic and research analysis. Further funding to complete the machine came from Research Corporation of America, in New York.
Presper Eckert and John Mauchly were the first to patent a digital computing device, their ENIAC computer. ABC had been examined by John Mauchly in June 1941, and is alleged to have influenced his later work on ENIAC, although Mauchly denied this. In 1967 Honeywell started a court case against Sperry Rand in an attempt to break their patent, based on the ABC being prior art. The court released its final judgement on October 19, 1973. In Sperry Rand Vs. Honeywell the court voided the ENIAC patent as a derivative of John Atanasoff's invention. The decision was not appealed.
Atanasoff was quite generous in stating, "there is enough credit for everyone in the invention and development of the electronic computer." Eckert and Mauchly received most of the credit for inventing the first electronic-digital computer. Historians now say that the Atanasoff-Berry computer was the first.
The original ABC was eventually dismantled, when the University converted the basement to classrooms, and most of its pieces were discarded. In 1997, a team of researchers from Ames Laboratory (located on the Iowa State campus) finished building a working replica of the Atanasoff-Berry Computer for a cost of $350,000. This replica dispelled any doubt over whether or not the ABC actually could perform the tasks it was designed to do. The new ABC is now on permanent display in the first floor lobby of the Durham Center for Computation and Communication at Iowa State University.
Anthony Ralston and Edwin D. Reilly (ed), Encyclopedia of Computer Science, 3rd Ed. , 1993, Van Nostrand Reinhold, New York ISBN 0442276796
See also: History of computing hardware