ICL 1900
| Designer | Ferranti-Packard/ICT/ICL |
|---|---|
| Bits | 24-bit |
| Introduced | 1964 |
| Design | CISC |
| Type | Register-Register Register-Memory Memory-Memory (move) |
| Encoding | Fixed |
| Branching | Comparison, carry, overflow, indexing, counting |
| Page size | 1024 words (1904A/S, 1906A/S, 1903T) |
| Extensions | extended floating point on 1906/7 |
| Registers | |
| General purpose | 8 24-bit (3 usable for indexing) |
| Floating point | 1 48-bit (96-bit if the extended floating point is present) |
ICT 1900 was the name given to a series of mainframe computers released by International Computers and Tabulators (ICT) and later International Computers Limited (ICL) during the 1960s and '70s. The 1900 series was notable for being one of the few non-American competitors to the IBM System/360, enjoying significant success in the European and Commonwealth markets.
In early 1963 ICT was in negotiations to buy the computer business of Ferranti. In order to sweeten the deal Ferranti demonstrated to ICT the Ferranti-Packard 6000 (FP6000) machine, developed by its Canadian subsidiary Ferranti-Packard.
The FP6000 was an advanced design, notably including hardware support for multiprogramming. ICT considered using the FP6000 as their medium-sized processor in the 1965–1968 timeframe, replacing the ICT 1302. Another plan being considered was to license a new range of machines being developed by RCA, probably compatible with the expected IBM 8000.
On 7 April 1964 IBM announced the System/360 series, a family of compatible machines spanning nearly the complete range of customer needs. It was immediately obvious that ICT would need a coherent response. Two paths were available: develop a range of machines based on the FP6000, using the flexibility of its design to produce smaller or larger machines, or cooperate with RCA who were re-targeting their development to a System/360 compatible range to be known as the RCA Spectra 70.
One major consideration was that the FP6000 was already running, while the RCA Spectra range would take some years to become available. In the end the decision was made to go with a range of machines based on the FP6000. The centrepiece of the new range was the ICT 1904, a version of the FP6000 with the ICT standard peripheral interface. For higher-end machines a new larger processor, the ICT 1906, was to be developed by the ICT West Gorton unit (formerly part of Ferranti). To meet the needs of smaller customers smaller machines, the ICT 1901 and ICT 1902/3 were developed by the ICT Stevenage unit, based on the PF182 and PF183 processors already in development.
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