IBM SSEC
During World War II, International Business Machines Corporation (IBM) funded and built an Automatic Sequence Controlled Calculator (ASCC) for Howard H. Aiken at Harvard University.
Watson and Aiken decided to go their separate ways, and IBM began work on a project to build their own larger and more visible machine.
[3] Astronomer Wallace John Eckert of Columbia University provided specifications for the new machine; the project budget of almost $1 million was an immense amount for the time.
[6] Modules were manufactured in IBM's facility at Endicott, New York, under Director of Engineering John McPherson after the basic design was ready in December 1945.
[8] The new machine, called the IBM Selective Sequence Electronic Calculator (SSEC), was ready to be installed by August 1947.
[6]: 143 The SSEC was installed on three sides of a room on the ground floor of a building near IBM's headquarters at 590 Madison Avenue in New York City, behind a large window where it was visible to people passing by on the busy street.
Approximately 12,500 vacuum tubes were used in the arithmetic unit, control, and its eight (relatively high-speed) registers, which had an access time of less than one millisecond.
Data that had to be retrieved quickly was held in electronic circuits; the remainder was stored in relays and as holes in three continuous card-stock tapes that filled another wall.
[17] Seeber had carefully designed the SSEC to treat instructions as data, so they could be modified and stored under program control.
IBM filed a patent based on the SSEC on January 19, 1949, which was later upheld as supporting the machine's stored program ability.
The serial nature of the paper tape memory made programming the SSEC more like the calculators from the World War II era.
For each new program, tapes and card decks were literally "loaded" on the readers, and a plugboard changed in the printer to modify output formatting.
The SSEC was also used for calculations by the U.S. Atomic Energy Commission for the ANP project to power an airplane with a nuclear reactor.
Robert D. Richtmyer of Los Alamos National Laboratory used the SSEC for some of the first large-scale applications of the Monte Carlo method.
The large array of flashing lights and noisy electro-mechanical relays made IBM very visible to the public.
[6]: 168 Subsequent computers would have electronic random access memory, and in fact the ability to execute instructions from processor registers was generally not adopted.
By 1951 the Ferranti Mark I was marketed in the UK as a commercial computer using Williams tube technology, followed by the UNIVAC I using delay-line memory in the US.
