The English Electric (later ICL) System 4 was a mainframe computer introduced in the mid-1960s. It was derived from the RCA Spectra 70 range, itself a clone of the IBM System 360 range. The models in the range included the System 4-10, 4-30, 4-50 (practically the same as the RCA 70/45), 4-70 (designed in English Electric) and 4-75. ICL documentation[1] also mentions a model 4-40. This was a slugged version of the 4-50, introduced when the 4-30 (intended to be the volume seller) was found to be underpowered and had to be withdrawn. The 4-10 was introduced as a satellite computer, but demand was very low, so it was withdrawn. Only the 4-50 and 4-70, and their successors, the 4-52 and 4-72, sold in any numbers. A slugged 4-72 (the 4-62) was introduced for sale in Eastern Europe.
The machines were essentially multi-programming batch computers. The System 4-75 was introduced in an attempt to cover the real-time/time-sharing market, but few were sold. One System 4-75 was used by the English Electric Computer Bureau subsidiary to develop and run the internally developed Interact 75 suite of time-sharing commercial packages for payroll and financial ledgers, but this proved unsuccessful, and the project was soon closed. System 4 proved itself to have very efficient communications and was the basis for several successful real-time processing applications.
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