GEC 4000 series

GEC 4000 series

The GEC 4000 was a series of 16/32-bit minicomputers produced by GEC Computers Ltd. of the UK during the 1970s and 1980s.


Elliott Automation became GEC Computers Limited after the data processing computer products had been passed over to ICT (which later became ICL). Elliott Automation retained the real-time computing systems, renaming itself Marconi Elliott Computer Systems Limited for a short time, and then renaming again to GEC Computers Ltd. GEC Computers retained the original but now aging Elliott 900 series, and needed to develop a new range of systems. Three ranges were identified, known internally as Alpha, Beta, and Gamma. Alpha appeared first and became the GEC 2050 8-bit minicomputer. Beta followed and became the GEC 4080. Gamma was never developed, so a few of its enhanced features were consequently pulled back into the GEC 4080. The principal designer of the GEC 4080 was Dr. Michael Melliar-Smith.

The GEC 4080 hardware and microcode included pioneering process management features. These allowed the efficient implementation of semaphores, asynchronous message passing, and context switching. [P. J. Denning, "ACM president's letter: computer architecture: some old ideas that haven't quite made it yet", "Communications of the ACM", 24 (9), 1981, page 553.]


Users of GEC 4000 series systems included many British university physics and engineering departments, the central computing service of University College London (Euclid) and Keele University, the JANET academic/research network X.25 switching backbone, Rutherford-Appleton Laboratory, Daresbury Laboratory, Harwell Laboratory, NERC, Met Office, CERN, ICI, British Telecom, SIP (Italian telco), Plessey, British Steel real-time control of rolling steel mills, British Rail and London Underground for real-time train scheduling, London Fire Brigade and Durham Fire Brigade command and control systems, Suffolk Constabulary, and most of the National Videotex systems in the world including the Prestel viewdata service.

At the Rutherford-Appleton Laboratory a GEC 4000 system was used to control the synchrotron and injectors used for the ISIS neutron spallation source until 1998.

A GEC 4080M was also used as the central processor for the radar system of the ill-fated Nimrod AEW.3 airborne early warning aircraft.


A number of variants of the GEC 4000 processor were produced, including (in approximate chronological order):

* 4080: original 1973 model with 64–256 KiB of core memory
* 4082: 4080 with up to 1 MiB of memory
* 4070: entry-level model without memory interleaving
* 4085: 4082 with semiconductor memory
* 4060: entry-level model based on AMD Am2900 bit-slice processors
* 4062/4065: 4060 supporting up to 1 MiB memory
* 4080M: compact ruggedized 4080 for military applications
* 4090: Am2900-based with 32-bit addressing extensions and up to 4 MiB of memory
* 4190: revised 4090 with up to 16 MiB memory
* 4180: cheaper, slower version of the 4190
* 4060M: compact ruggedized 4060 for military applications
* 4160: 4060 with 4090 instruction set extensions
* 4150: desktop 4160
* 4162: 4160 with additional communications controllers
* 4195: compact 4190
* 4185: cheaper, slower version of the 4195
* 4151: rackmount 4150
* 4190D: dual-processor 4190
* 4193: 4195 with SCSI adaptor
* 4220: gate array processor implementation
* 4310: Motorola MVME187-based system emulating a GEC 4220


Several operating systems were available for the GEC 4000 series, including the following:

* COS: Core Operating System, for diskless real-time systems
* DOS: Disk Operating System, for real-time systems, providing a filesystem and swapping facilities
* OS4000: a multi-user system supporting batch and interactive use, and transaction processing

Programming languages available included BABBAGE (a high-level assembly language), FORTRAN IV, CORAL 66, ALGOL and BASIC.


* [ 25 years of GEC 4000 series]
* [ "GEC 4000 family", "Which Computer?", May 1979]

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