GEC 4000 series processors

The following summary of the 4000 series processors is in roughly chronological order.

4080 (1973)

[4080 front panel]

The 4080 is the original 4000 series processor. A 4080 system could support up to 256kb of core store, although this would have been an unthinkable amount when the system was developed - the first one was shipped with 64kb. The system was mostly 16bit, with 32bit and some 64bit instructions. I/O was performed by the BMC, Basic Multiplexor Channel, a second dedicated processor. Up to 3 further I/O processors could be fitted, but for most applications, one was perfectly adiquate.

The original 1973 Sales Brochure makes for interesting reading, including the technical specification.

4082 (1976)

By this time, the 256kb store limit was becoming quite a serious limitation. The 4082 is a 4080 with 2 extra store address lines, so it can support 1Mb of core store. However, the BMC was still limited to accessing only the bottom 256kb of store. This was not a serious problem except for overlays (virtual memory swapping to disc), and for this, a second I/O processor was added which could access all of store but could only drive a single disc controller; this was known as an EDC, External Disc Channel.

4070 (1976)

The 4070 was introduced as a poor man's version of the 4082. Core store was slow, and to gain performance, the 4080/4082 could interleave store accesses, i.e. it could perform simultaneous access to multiple store locations. The 4070 had the store interleaving switched off. It was sold at a lower price, and later the customer could pay for an upgrade to a 4082 to gain performance. The 4070 could support 512kb of core store (this was probably a marketing limitation, the technical limitation almost certainly being 1Mb like the 4082).

4085 (1978)

The 4085 is a 4082 with semi-conductor store, making it faster than the 4082. The new semi-conductor store could also be used to add semi-conductor memory to existing 4082 core memory systems.

4060 (1979)

[4060 front panel] This 4060 has a full front panel (DMCU), most only had the bottom row.

The 4060 replaced the 4070 as the entry level processor. It used 4 AMD 2900 bit-slice processors (4 bits wide each) as its main CPU, microprogrammed to run the 4080 instruction set. The 4060 also had its main I/O processor (called the IMC, Integral Multiplexor Channel) as part of the main CPU microprogram, although additional external I/O processors could be fitted if required. The 4060 supported 256kb of internal semi-conductor store.

4062 (1979)

The 4062 was a varient of the 4060 which supported 1Mb of store, either core or mixed core/semi-conductor.

4065 (1979)

The 4065 is a 4060 which could support 1Mb of semi-conductor memory.

4080M (1979)


Ruggedised and minaturized version of the 4080 for defense use.

4090 (1981)

[4090 front]

The 4090 was the first processor which significantly extended the 4080's original instruction set. The processor was a 32bit processor based on 8 AMD 2900 bit slice processors, and was the first British 32 bit minicomputer. The CPU instruction set was backwards compatible with the 4080, but also added 32bit addressing. The system supported up to 4Mb of main memory, but this was still the same external memory crates used by the 4082/4085, and they had to be paired up to make a 32bit wide memory bus for the 4090. However, it introduced a 16kb memory cache. The main I/O processor used was an EMC/4, External Multiplexor Channel, which could address all 4Mb of main memory, although other I/O processors could be added.

4190 (1982)

The 4190 was basically a hardware tidy up of the 4090. The old 4082/4085 external memory crates for a 4Mb 4090 system required several 6 foot tall 19" racks, and this was all replaced with internal memory on the 4190 (using the same 32bit memory boards as the GEC Series 63). This enabled the system to address up to 16Mb of main memory. The instruction set and appearance of the machine was unchanged from the 4090 (except for loss of external memory racks).

A new I/O processor, the FMC, Fast Multiplexor Channel, was developed, and this was the first 32bit wide I/O processor. (The company never actually developed any 32bit controllers for the FMC, continuing to use the existing 16bit controllers in it. However, one customer did develop a 32bit controller for it - a fast parallel I/O card which could be used as an inter-machine link.)

4180 (1982)

The 4180 was a 4190 with the fast multiplier board and the memory cache removed. This made the system slightly cheaper, but more significantly, enabled it to be sold into countries where export of components in these parts was not permitted at the time.


Ruggedised and minaturized version of the 4060 for defense use.


The 4160 was an update to the 4065 microprogram to include the additional instructions added to the 4090. These were mostly 32bit instructions, but as the 4160 remained a 16bit processor at the hardware level, it didn't perform the 32bit instructions very fast.

4150 (1982)


The 4150 is a 4160 with fewer card slots in a desktop case. A CDC LARK disc mechanism was available in a matching case.

4162 (1986)

The 4162 was a modification to the 4160 to allow DMAD type I/O processors to be fitted for high speed comms controllers.

4195 (1986)

The 4195 was a 4190 with the FMC included in the CPU crate, which reduced the physical size of the system. It had fewer memory slots (but larger memory boards meant it could still take the full 16Mb) and fewer connections for external I/O processors, but these were rarely used.

4185 (1986)

The 4185 was a 4195 with the fast multiplier board and the memory cache removed (like 4180/4190 comparison).

4151 (1987)

The 4151 is a 4150 designed for mounting in a customer-provided 19" rack.

4190D (1987)

The 4190D was a dual processor 4190. Only one was ever sold.


The 4193 was similar to the 4195, but the FMC was swapped for a SCSI I/O processor instead.

4220 (1987)

The 4220 was a significant hardware change from the 41xx range, although the instruction set remained unchanged. The processor was implemented using Gate Array technology on a single board. The store and cache system were redesigned too.


The 4230 was a dual processor version of the 4220. None were ever sold, although it worked well in-house.

4310 (1993?)

The 4310 was another significant hardware change. The 4310 uses Motorola's MVME187 88100 based VME system, and runs a 4000 series instruction interpretor. Systems are available in 19" rack mounting cases, pedistalls looking like PC tower systems, and pizza boxes. The 4310 series does not support any of the earlier 4000 series peripheral controllers. It has an IMC I/O processor (like the 4x6x) for the on-board peripherals (serial ports, ethernet, clock, interval timer, SCSI), and external VME-based I/O processors for additional cards such as multi-port async or X.25.

© 1997 Andrew Gabriel. All Rights Reserved. / Last revision 12 October 1997