English Electric System 4

It was derived from the RCA Spectra 70 range, itself a variant of the IBM System 360 architecture.

[1] The models in the range included the System 4-10 (cancelled), 4-30 (1967), 4-50 (1967, practically the same as the RCA 70/45), 4-70 (1968, designed by English Electric)[2] and 4-75.

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of the 4-50, introduced when the 4-30 (intended to be the volume seller) was found to be underpowered and had to be withdrawn.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 System 4-50 and 4-70 were intended for real-time applications, for they had four processor states, each with its own set of general-purpose registers (GPR).

In the case of power failure, the processor saved the volatile registers before shutting itself down in an orderly fashion.

[6] Instruction times (microseconds) were as follows:[7] The System 4 could be supplied with medium-speed or high-speed card readers.

In about 1971, the then supplier, ICL, rewrote I/O modules to remove trailing blanks on input and output, and to block to 384 bytes, which improved performance considerably.

System 4 proved itself to have very efficient communications and was the basis for several successful real-time processing applications.

Another 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.