International Computers and Tabulators

International Computers and Tabulators or ICT was formed in 1959 by a merger of the British Tabulating Machine Company (BTM) and Powers-Samas. In 1963 it also added the business computer divisions of Ferranti. It exported computers to many countries around the world and went on to become part of International Computers Limited (ICL).

The ICT 1101 was known as the EMIDEC 1100 computer before the acquisition of the EMI Computing Services Division who designed and produced it.

The ICT 1201 computer used thermionic valve technology and its main memory was drum storage. Input was from 80-column punched cards and output was to 80-column cards and a printer. Before the merger, under BTM, this had been known as the HEC4 (Hollerith Electronic Computer, fourth version).

The drum memory held 1K of 40-bit words. The computer was programmed using binary machine code instructions. When programming the 1201, the machine code instructions were not sequential but were spaced to allow for the drum's rotation. This ensured the next instruction was passing under the drum's read heads just as the current instruction had been executed.

The ICT 1301, and its smaller cousin the ICT 1300, used germanium transistors and core memory. Backing store was magnetic drum, and optionally one-inch-, half-inch- or quarter-inch-wide magnetic tape. Input was from 80-column punched cards and optionally 160-column punched cards and punched paper tape. Output was to 80-column punched cards, printer and optionally to punched paper tape. The first customer delivery was in 1962, a 1301 sold to the University of London. One of their main attractions was that they performed British currency calculations (pounds, shillings and pence) in hardware. They also had the advantage of programmers not having to learn binary or octal arithmetic as the instruction set was pure decimal and the arithmetic unit had no binary mode, only decimal or pounds, shillings and pence. Its clock ran at 1 MHz. The London University machine still exists (January 2006) and is being reinstated to working condition by a group of enthusiasts.

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