IBM SSEC

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The IBM Selective Sequence Electronic Calculator (SSEC), also called Poppa, was an electomechanical computer built by IBM, finished in January 1948.

The IBM Selective Sequence Electronic Calculator (SSEC), dedicated in 1948 by Thomas J. Watson, Sr., at IBM's headquarters at 590 Madison Avenue in New York City, was the first operating computer to combine electronic computation with stored instructions and it was the last of the large electromechanical computers ever built. It was the first computer to run a stored program, although the computer was not fully electronic. Wallace J. Eckert was in charge of the development of the SSEC. It was placed on the ground floor of IBM's main office building in New York City, where it was visible to people on the sidewalk. It was demonstrated to the public on January 27, 1948 and ran until August 1952, when it was dismantled, having been made obsolete by electronic computers.

The SSEC, a hybrid of vacuum tubes and electromechanical relays, combined the speed of electronic circuits with a storage capacity of 400,000 digits. Approximately 13,500 vacuum tubes were used in the arithmetic unit and its eight high-speed registers, which had an access time of under 1 millisecond. SSEC had 21,400 relays that were used for control and 150 slower-speed registers, with an access time of 20 milliseconds. The arithmetic unit of the SSEC was a modified IBM 603 electronic multiplier. Addition took 285 microseconds and multiplication took 20,000 microseconds, making it approximately 100 times faster than the Harvard Mark I. Data which had to be retrieved quickly were held in electronic circuits while the remainder were stored in relays and as holes in continuous card stock tapes.

The SSEC was very reliable for its time, making about one error for every eight hours of operation. It was used for calculations by the U.S. Atomic Energy Commission and for calculating the positions of planets. The SSEC produced the moon-position tables used for plotting the course of the 1969 Apollo flight to the moon.

[edit] References

IBM SSEC Control Desk photo
IBM Archives: FAQ's for Products and Services
Moreau, René (1984). The Computer Comes of Age: The People, the Hardware, and the Software. MIT Press. ISBN 0-262-13194-3.
Cruz, Frank da (Feb 17, 2005). The IBM Selective Sequence Electronic Calculator. Columbia University Computing History. Retrieved on October, 2006.