GEC 4000 series
The 4000 series systems were developed and manufactured in the UK at GEC Computers' Borehamwood offices in Elstree Way.
Development and manufacture transferred to the company's new factories in Woodside Estate, Dunstable in the late 1970s.
will pass a message to the relevant trusted process which it will vet before performing the action and replying.
It has 8-bit bytes, big-endian, byte-addressable memory, two's complement arithmetic, and base-16 excess-64 floating point format (same as IBM System/360).
A read-only 'keys' register allows programs to read the value set on the front panel toggle switches by the operations staff.
There are a set of string manipulation instructions which operate on variable lengths of store, copying, comparing, or scanning for a pattern.
In Basic Test mode, Nucleus is disabled, I/O is performed differently, and only a single program can run, restricted to the bottom 64KiB of store, but all other non-nucleus and non-PAS instructions operate normally.
The 4000 I/O design is based around a number of Input/Output Processors known as IOPs, each of which interfaces between the store and a set of I/O controllers.
The I/O controllers on each IOP would each occupy one or more Ways, depending on how many simultaneous I/O operations they need to handle.
The earlier IOPs performed 8-bit and 16-bit wide store accesses, with a burst mode for doing up to 8 transfers together for higher throughput I/O controllers.
The entry level 415x and 4x6x systems have their first IOP (Integral Multiplexer Channel, or IMC) integrated into the Nucleus firmware, and thus I/O operations on the IMC did have some impact on CPU performance, although the 4x6x systems could have external IOPs added.
A digital I/O board (using four Ways) was commonly used for direct process control interfacing, and for providing a fast parallel link between systems.
The earlier GEC 2050 minicomputer used an 8-bit version of the Normal Interface, and most I/O Controllers could be used on both ranges of systems.
A SCSI IOP generated a SCSI bus for attaching more modern disks, and also included an integrated Interval Timer, system console controller, and Calendar Clock so that an additional Normal Interface IOP and separate controllers was not required to support just these functions.
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,[8] Daresbury Laboratory, Harwell Laboratory, NERC, Met Office, CERN, ICI, British Telecom, SIP (Italian telco), and Plessey.
The computers controlled most of the world's national Videotex systems, 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 used as the central processor for the radar system of the ill-fated Nimrod AEW.3 airborne early warning aircraft.
[9] The Central Electricity Generating Board used GEC 4080 processors at three of their Grid Control Centres.
