ENIAC - Comparison With Other Early Computers

Comparison With Other Early Computers

Mechanical and electrical computing machines have been around since the 19th century, but the 1930s and 1940s are considered the beginning of the modern computer era.

• The German Z3 (shown working in May 1941) was designed by Konrad Zuse. It was the first general-purpose digital computer, but it was electromechanical, rather than electronic, as it used relays for all functions. It computed logically using binary arithmetic. It was programmable by punched tape, but lacked the conditional branch. While not designed for Turing-completeness, it accidentally was, as it was found out in 1998 (but to exploit this Turing-completeness, complex, clever hacks were necessary). It was destroyed in a bombing raid on Berlin in December 1943.
• The American Atanasoff–Berry Computer (ABC) (shown working in summer 1941) was the first electronic computing device. It implemented binary computation with vacuum tubes but was not general purpose, being limited to solving systems of linear equations. It also did not exploit electronic computing speeds, being limited by a rotating capacitor drum memory and an input-output system that was intended to write intermediate results to paper cards. It was manually controlled and was not programmable.
• The ten British Colossus computers (used for cryptanalysis starting in 1943) were designed by Tommy Flowers. The Colossus computers were digital, electronic, and were programmed by plugboard and switches, but they were dedicated to code breaking and not general purpose.
• Howard Aiken's 1944 Harvard Mark I was programmed by punched tape and used relays. It performed general math functions, but lacked any branching.
• ENIAC was, like the Z3 and Mark I, able to run an arbitrary sequence of mathematical operations, but did not read them from a tape. Like the Colossus, it was programmed by plugboard and switches. ENIAC combined full, Turing complete programmability with electronic speed.

The ABC, ENIAC and Colossus all used thermionic valves (vacuum tubes). ENIAC's registers performed decimal arithmetic, rather than binary arithmetic like the Z3 or the Atanasoff-Berry Computer.

Until 1948, ENIAC required rewiring to reprogram, like the Colossus. The idea of the stored-program computer with combined memory for program and data was conceived during the development of ENIAC, but it was not initially implemented in ENIAC because World War II priorities required the machine to be completed quickly, and ENIAC's 20 storage locations would be too small to hold data and programs.