Atanasoff - Berry Computer ( ABC )

The Atanasoff – Berry Computer (ABC)  was the first electronic computer, designed and built by Lowa State College Mathematics and Physics professor John Vincent Atanasoff and his assistant, Clifford E. Berry ( a graduate student) . They worked in the basement of the physics building at Lowa State College on the computer from 1939 until 1942 when it was abandoned due to World War II . Unfortunately, after being abandoned , it was neglected and eventually disassembled for parts. In 1994, a team from Lowa state University began to rebuild the computer, finishing it in 1997. The system 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. The idea behind the ABC were later used in the construction of the ENIAC, the world’s first general purpose computer.

Purpose / Working

ABC was designed only to solve systems of linear equations and was successfully tested in 1942. It could handle systems with up to 29 equations, a difficult problem for the time. Problems of this scale were becoming common in Physics, the department in which John Atanasoff worked. Such math problems were very challenging and time consuming, and often encountered by scientists and engineers.

The machine 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 be repeated manually for each of the equations, which would result in a system of equations with one fewer variable. Then the whole process would be repeated to eliminate another variable.

George W. Snedecor, the head of Iowa State's Statistics Department, was the first user of an electronic digital computer to solve real-world mathematics problems.

Components of ABC

It was not a Turing complete computer. The machine was  the first to implement three critical ideas that are still part of every modern computer :-

1.   Using binary digits to represent all numbers and data

2.   Performing all calculations using electronics rather than wheels, ratchets, or mechanical switches

3.   Organizing a system in which computation and memory are separated.

The memory of the Atanasoff–Berry Computer was regenerative capacitor memory, which consisted of 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 two 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 alternating current power line frequency of 60 Hz was the primary clock rate for the lowest-level operations. The arithmetic logic functions were fully electronic, implemented with vacuum tubes. The family of logic gates ranged from inverters to two and three input gates. The control logic functions, which only needed to operate once per drum rotation and therefore did not require electronic speed, were electromechanical.  An operator was needed to operate the control switches to set up its functions, much like the electro-mechanical calculators and unit record equipment of the time. 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. Intermediate results were binary, written onto paper sheets by electrostatically modifying the resistance at 1500 locations to represent 30 of the 50-bit numbers (one equation). 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. 

Implanted

The original ABC was eventually dismantled in 1948, when the University converted the basement to classrooms, and all of its pieces except for one memory drum were discarded.

In 1997, a team of researchers led by John Gustafson from Ames Laboratory located on the Iowa State campus  finished building a working replica of the Atanasoff–Berry Computer at a cost of $350,000 (equivalent to $0.53 million in 2017). The replica ABC is now on permanent display in the first floor lobby of the Durham Center for Computation and Communication at Iowa State University. As of May 2012, it is on loan to the Computer History Museum in Mountain View, California for a major exhibition.