ACD Atlas Computing Division ICF: GEC Systems

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GEC 4000 family

May 1979

Which Computer?

It was in 1968 that the real-time computing interests of AEI, Elliott-Automation, English Electric and Marconi together with those of GEC, were consolidated under Government inspiration into a single company. It traded initially as Marconi Elliott Computer Systems Ltd until registration in its present name of GEC Computers Ltd could be completed.

The company was set up as a design and manufacturing centre for the multi-faceted GEC group, as well as an independent computer supplier. Today it employs more than 900 staff and with orders worth £22 million for this year, more expansion at its new manufacturing plant in Dunstable seems inevitable.

GEC Computers has a good reputation for providing reliable real-time and process control computers especially for military environments and for use by other companies in the group. The 2050, an 8-bit machine, has been used widely in the real-time and communications market since its introduction in 1972. It is used in the public sector, including the Post Office, especially for remote job entry to a mainframe. There are also a few customers fro the SRS version, a stand-alone seat reservations system promoted among football clubs - user include Manchester United and Fulham.

The arrival of the more powerful 16-bit 4000 series is 1973 gave GEC Computers a basis for a much wider attack on the market. The opportunity to build on the 4000 series was helped by two important factors - public sector bodies, such as the Post Office and universities, are directed to buy British; and it had a ready made market within the GEC group, whose members are encouraged, although not compelled, to buy from GEC Computers.

GEC Computers traditionally has strong links with the university market, providing front-end computers for the ICL 1900as well as stand-alone machines. More recently its involvement with the EPSS packet-switching system and Prestel have involved a number of Post Office contracts for 4000s. the order book for 4000s stands at 260 systems with 200 installed.

GEC COMPUTERS provides a range of software-compatible 16-bit minicomputers. The low end of the family consists of the three machines, the 4060, 4062 and 4065, all of which may be mounted in a desk-style unit. They vary only in the type and capacity of storage available, and are the latest additions to the 4000 range. The 4062 can have a mixture of core and semiconductor store up to one megabyte; the other two machines use semiconductor memory, with the 4060 having a maximum of 256KB and the 4065 having an upper limit of 1MB.

GEC has been slow to introduce semiconductor memory. Two years ago it was the norm on U.S. minis, offering cost savings and lower power and cooling requirement than the older technology of ferrite cores.

More reliable

With the new semiconductor-based machines GEC has taken the architecture of its larger and more expensive 4070/4080 minis and implemented it with more LSI circuitry and lower internal speeds to produce a reasonable entry-level price. The 4060 needs two printed circuit boards for the CPU and not 15; it uses 64KB semiconductor memory cards, rather than the older core boards which stored half that amount. The design includes a separate I/O processor (another PCB), there is a good deal of built-in self-testing, and the more compact approach means less cabling, less heat, and more reliability.

Higher up the range are the 4070 and 4080. They have a variety of memory, tapes and a greater expansion capability, though no 4000 model can have more than one megabyte of directly-accessible storage, a fairly low limit by comparison with some mid-range U.S. minis.

System software

There are three operating systems for the 4000. Although described by GEC Computers as different, they share some common functions - all are multiprogramming, too - and so can be regarded as an upgrade path. COS is a core-only system, DOS a minimal disc operating system but OS4000 is the one most users will meet outside the real-time environment.

A pioneer

The strengths of the 4OOO series lie particularly in its operating system and related features. OS4000 is a multiprogramming, multi-access operating system supporting a segmented virtual memory; the important scheduling and address-mapping functions are provided by a nucleus which is implemented in fast-access firmware - GEC was among the pioneers of this technique. This method provides the following advantages.

OPUS, released in Autumn, 1975, is the principal GEC involvement in multi-access operation and is a packaged system based on the OS 4000 operating system, together with a selection of elements from the GEC hardware catalogue. It is now a proven mainline multi-terminal, timesharing system. which can support system development and run applications programs simultaneously. OS400 now is generally issued in the OPUS form.

OPUS supports up to 32 time-sharing terminals. They can be running interactively or they may be devoted to specific background batch jobs - like RJE, for which emulator packages are becoming available, or printer spooling. The principal OPUS/OS4000 languages are:

Other significant system software includes a sort-merge, an indexed sequential access method, and an 0S4000 enhancement to provide true transaction processing.

Undergoing field trials at a number of customer sites is an implementation of the Cincom Systems TOTAL package. TOTAL is the worlds' best-selling database manager and is available on several other computers. When it is tested fully and released for implementation on the 4000., TOTAL will add considerably to its attraction for applications involving large amounts of data organised in relatively complicated arrangements.

The company has commissioned a suite of commercial software, including sales ledger, purchase ledger, nominal ledger and payroll, now due to be handed over. The applications will have field trials in GEC Computers before being released.

Model Characteristics
Model Memory size (Kb) Memory Type Cycle time of memory in nanoseconds
Min Max Core S/C Mixed
4060 64 256 Yes 550-600
4062 64 1024 Yes 550-600
4065 64 1024 Yes 550-600
4070 64 512 Yes 800
4080 32 256 Yes 550
4080M* 32 256 Yes 550
4082 128 1024 Yes 665**
4085 128 1024 Yes 550-600

* Miniaturised and ruggedised 4080

4-way interleaved memory of 32K blocks; each block has 800ns cycle, so the nominal cycle is equivalent to 665ns.

After this article, GEC produced a 4090 system in 1981 and some further systems in the period to 1987 at least.

Model Instruction times in microseconds
(double precision in brackets)
Floating point 32-bit operands
Add Multiply Divide Reg Add Multiply Divide
4060 2.3 6.3(6.7) (10.09) 1.9 7.2 11.5 12.7
4062 2.3 6.3(6.7) (10.09) 1.9 7.2 11.5 12.7
4065 2.3 6.3(6.7) (10.09) 1.9 7.2 11.5 12.7
4070 1.6 4.1(6.35) 7.1(20.85) 1.8 6.45 11.65 20.15
4080M* 1.1 3.6(5.85) 6.6(20.35) 1.55 5.8 10.9 19.4
4082* 1.1 3.6(5.85) 6.6(20.35) 1.55 5.8 10.9 19.4

* all times for the 4082 are quoted using a nominal cycle time of 800 nanoseconds


The instruction set provides operations on single bytes, variable-length strings of bytes, integers of 16 and 32 bits, and single bits within a 16-bit word.

The hardware supports multi-programming for up to 256 independently-scheduled processes; a set of hardware base and range registers (the Segment Registers) protect the store occupied by the component segments of the processes from unauthorised access by another process, while allowing the sharing of code and data between processes in a flexible and controlled manner.

Commercial Aspirations

GEC COMPUTERS has had interests in the commercial market with the use of the 2050 as an RJE terminal but with the continuing development of its systems software, particularly the multi-user operating system and the provision of new business-orientated languages, it hopes to gain some share of the market; although this might prove hard against fierce competition from the many systems houses already established in this area.

Business applications are reportedly being developed and GEC Computers certainly has links with a number or top software houses - Data Logic, Systems Designers and SPL. Smaller organisations looking to specialise on the GEC 4000 include Ian Martin Computers Ltd and John Bell Associates.

Processor and memory
Word length 16 bits
Addressing: direct, indirect, relative, indexed 64K of virtual memory/process. Nucleus performs address mapping consisting of offsets to base registers for up to four current 16K segments. A process may have up to 255 segments but only four are current.
  • Two 32-bit registers
  • A-Accumulator
  • B-Auxiliary accumulators
  • Five 16-bit registers
    • X-index register
    • S-sequence register
    • L-local workspace pointer
    • Z & Y-base registers
  • One 8-bit register
  • C-status byte
User microprogramming No
Hardware floating point Yes, as standard
Instruction set 160, including floating point with special string and bit manipulations.
Instruction times
in microseconds
Floating point in microseconds See table

Multiplexed I/O channel transferring at up to 300KB for autonomous half-word (16-bit) transfers or up to 900KB/sec at burst rates.

External multiplexed channel, external disc/drum channel, for extra fast I/O processing at up to 2MB per microsecond.

Programmed I/O Yes; semaphore drives I/O under program control if desired.
Maximum number of devices addressable Nominally 256
Main memory type May be core or semiconductor, or a mixture of both (see table).
Mapping Nucleus performs address mapping into current 64K of segmented virtual storage, using firmware.
Memory range From 64KB to 1MB (see-table for details).

Core in 32KB increments, semiconductor in 64KB increments.

The 4082 needs 4 × 32 = 128KB increments, because of four-way inter-leaving.

Cycle times 550-600 nanoseconds (see table for details).
Memory protection Yes, using base and limit on access to segmented memory.
Error correction Nucleus provides error trapping and failed processes can be re-scheduled or hung up. Semiconductor stores use Hamming codes for single error-correction and double error-detection.
Parity checks Yes and CRC on communications lines
Cache memory No
Proven but not outdated architecture Conceptually sound
Part of compatible range Yes
Mass storage
Disc -Purchased
-cartridge: 4-8MB removable/fixed; transfer rate using interlaced sector transfers = 123KB/sec to normal interface.
Four drives per controller
-fixed discs: 35MB and 70MB, four drives per controller. 270MB disc has been proposed.
Drum -head per track
-1, 2, 4MB capacity
Transfer rate varies between 110KB and 440KB per second, depending upon interface.
Mag tape 9-track, 800bpi and 1600bpi and switchable; transfer rate 30Hz
Cartridge tape Available
Max no per system Under OS4000 using transactional environment, 64; multi-access users, 32. Local attachment up to 300 metres.
Long line drivers Not provided by GEC, but accommodated easily
Interfaces available RS232, V24
Attitude to OEM terminals Driver software has been designed around own terminals. GEC will accommodate OEM terminals but makes it clear they are the user's responsibility.
Easy attachment of extra/or non-standard terminals Interface contention unit provides ability to add extra Teletype-compatible terminals. A variety of communications controllers allow attachment of other non-standard terminals. Non-standard in GEC-parlance usually means only terminals for which GEC does not provide documentation, service support, cables or controllers, so connection is at owners' risk.
Communications and Teleprocessing Communication Extensive range of communications controllers is available, including:
-inter-processor links
-four-channel comms controller
-full range of barrier protocols approved by Post Office
-front-end processing for ICL 1900 series by emulation of ICL 7903 communications processor - GEC is working on X25 to provide a micro-based controller for 9,600 baud. Available now is the middle High Level Data Link Control (HDLC) link to link protocol.
-can support CAMAC: interfaces for A/D converters.
Teleprocessing Multiform 4000 screen formatting and file manipulation software is available.
Other peripherals
Printers Dot matrix
80 col 100cps
-132 col 165cps
Line printers
-136 col 300lpm
-136 col 60lpm
-136 col 1,250lpm
Thermal printer
-300 cps
Paper Tape 700cps reader, 350cps reader, 110 cps punch
Card 285 cpm reader, 600 cpm reader
System software
Operating systems COS - real-time multiprogramming operating system for core-based systems only.
DOS - Disc operating system for similar real-time and process control work. Features multiprogramming, overlays, user-defined partitions
OS4000 - most sophisticated operating system both for program development and applications featuring:
-output spooling
supports batch, transaction processing, multi-access, RJE and combination of these environments being set up at system generation time.
All 4000 processors have a built-in hardware real-time executive called Nucleus, which performs the following functions:
-address mapping
-message passing
-I/O control
-semaphore handling.
Principal system software other than OS Index Sequential Access Method (ISAM)
Information retrieval (STATUS II)
Data Base Management (TOTAL)
Utilities: sort merge, macro generators MGEN and ML1, text editor, PERT, multiform 4000
Digital plotter 35 and 90cm drum plotters; interface and support software available for Versatek range of printer/plotters


GEC prefers to quote prices for specific customer requirements. Competition in business and commercial computing may mean the policy will change. Prices here were quoted last month to Computermarket visitors.

Standard Configuration

GEC4060 System 1

£33,350 plus £3.300 maintenance

System 2

£53,000 plus £5,875 maintenance

System 3

as System 2 but :

£63,380 plus £7,300 maintenance

GEC 4065 System 4

£120,750 plus £12,600 maintenance

GEC 4085 System 5

£214,000 plus £17,800 maintenance

Prices do not include VDUs, which should cost around £1,000 per unit.