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M > MERLIN > M4000   


The BT Merlin M4000 is a very obscure computer from the mid 1980s. It is allegedly based on the Logica Kennett, and should not be confused with the BT Merlin Tonto which is a rebadged ICL OPD.

The exact application of M4000 is unknown, but it was almost certainly developed for internal use by BT and never sold on the open market. It could have been used in conjunction with System X telephone exchanges.


Contributors: Riaz Sobrany

Stevie Skellett (UK) reports:
These machines were certainly used outside of BT. The Royal Navy used them for admin tasks in the 80's. The machine I used had a 3.5" 720K floppy drive and a 20MB 'Winchester' hard disk. The OS was Concurrent DOS if I remember right. You could have 4 virtual terminals selected from a keyboard key. We had a vastly underrated, if not very user friendly, WP package called Lex9b. Once you learnt all its tricks, many of which did not figure in our user documentation, you could really make it sing. Mine also had another, similar sized, unit containing the Tape Backup Drive - backups took a *long* time!

Ray Chester adds:
The DSS used these computers. Installed and maintained by BT Merlin. The systems were built for specific functions for example "Social Fund" had a couple of units with Social fund software and a Dot matricx printer. These machines would keel over from any passing static charge. They also had the Asteroids game written for them lol

Col comments:
My introduction to IT. I worked on these for 5 years or so. These were used extensively outside BT. Major government contracts (as above post mentions), used by the armed forces and small companies such as solicitors etc. Also used by most of the theatres in the UK, using a box office app called RITA. They ran bespoke software apps and also had a word processor app called "Merlinword". Other variants had single floppy and 10 or 20meg hard drive. Also an 80meg hard drive or a Tandberg tape drive in its own casing. The RITA system even networked these together, using ARCNET. The nodes were addressed by using jumpers on a network daughter board. Oh happy days !

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The M4000 range was used across several major contracts. These included OASIS for the Royal Navy, RITA - ticketing for theatres, DSS case paper location with Siemens and Wenger printers. Plus some specials such as the post room in the basement of Buckingham Palace and in the Houses of Parliament. I used to work for BT Business Systems, Walpole House in Ealing and covered the country as a field engineer. The M4000 had additional memory cards located below the main motherboard, an Arcnet network card and additional support for two more screens and keyboards via another adapter card. The M4000 was effectively the Logica Kennet and the Kennet versions were used in GP Surgeries and NHS sites by a third party company called Vamp Health, now known as In Practice Systems Ltd. As stated elsewhere, The Forestry Commission used quite a few of these around its UK sites. They were also sold to other government departments with MerlinWord and Ricoh 1600 daisywheel printers for word processing in big typing pools.

Thursday 2nd October 2014
John Desmond (Surrey/UK)

I worked for BT AT (Applied Technology - an early consultancy and external systems developer, in the now common style) in Newcastle from ''85 to ''87, mostly on a large project for the D(H)SS. We only had a handful of PCs and rather more of the M4000s running CPM/86. We regarded these as far better than the IBMs! The amber monitors were clearer than IBM''s blurry greens and the build quality of the hardware was rock-solid (Logica did know how to build a good boat anchor). Best of all though was the multiprocessing capability of CPM/86 and the four virtual screens with rapid hot-key switching between them.

Software was much the same as MS/DOS, at least where things had been ported. Most of my work was Pascal programming, using Prospero Pascal (that I''d used since Z80 CP/M) and Wordstar as an editor.

The biggest project I did with the M4000 was part of the broader DHSS project. This was a terminal concentrator / forms interpreter running on ITL minis (a dinosaur even then). To test this and emulate an office full of busy typists we (well, I and Dr Russell Mulcahy) built a network of 20 M4000s, networked with ArcNET. Each M4000 had smart serial cards (on-board processor) installed so that it could run 4 serial connections simultaneously. A typist-emulator script could be run across 80 instances at once, using CPM/86''s multi-tasking so that the script interpreter only needed to be a simple single-thread program. The whole system was so successful for testing that the DHSS bought a complete duplicate for their own tests.

Tuesday 7th February 2012
Andy Dingley (South Wales)

BT Merlin M4000 (Logiva VTS-2400 "Kennet")

I worked for Logica VTS in Swindon between 1984 and 1986 (when VTS was closed) in the software development division. At the time I joined the main product was the VTS-2200 (internally called "Whirlwind") dedicated Word Processing system, based on the Intel 8086 running custom software (Firmware, OS and WP application) and with 1 or 2 40 track 5.25" floppy disks and monochrome text only displays. These were also re-badged by ICL (as the DRS-8801), British Telecom (as the M3300) and Nexos. They could be networked on a Cambridge Ring and were also used internally as development workstations running an Intel development system (8086 assembler and PL/M-86).

The next generation machine developed by VTS was the VTS-2400 or "Kennet". The Kennet was also based on the Intel 8086, but was designed as a more general purpose office computer in the style of an IBM PC system unit. It could have various combinations of storage devices, 1 or 2 80 track 5.25" floppy disks, 1 or 2 internal 10Mb Rodime Winchesters, an external 76Mb Fujitsu Winchester and/or an external 150Mb Tandberg QIC tape unit. They were reasonably modular, able to take additional cards for networking (Cambridge Ring or ArcNet, IBM Sync. Comms cards), additional memory, multi-port serial cards etc. It also had bitmapped graphics (initially monochrome, and later, a colour prototype).

In addition to the Word Processing software, MS-DOS and CCP/M-86 (later Concurrent DOS) were ported to the machine, allowing general office applications to run on the system, and I seem to remember a project that ported GEM (Digital Research's graphical windowed system - an early competitor to Microsoft Windows).

However, the Kennet was NOT IBM PC compatible, and so could not run the major business applications around at the time as these were tied to the IBM PC hardware. There were limited sales into specific projects, and the product was badged by BT (as the Merlin M4000). After VTS closed, British Telecom funded an independent team of software developers (Cognosys Limited) to port the Wordprocessing Software to their next generation of IBM PC compatible machines (based on Zenith hardware). This was to be called "Merlinword 5000", but I'm not at all sure it ever saw the light of day as a commercial product. Cognosys also developed a module for a document exchange system called CrossPak to allow migration of documents in the VTS WP system format to other PC compatible systems.

Ray Chester and Chris Timson are correct in mentioning the DSS use of Kennets. I was the consultant who worked with the DSS development team in Reading for 3 months (having been in the Logica VTS team that ported MS-DOS and CDOS to the Kennet). And am slightly embarrassed to admit that I also wrote the "Asteroids" game mentioned (initially as a demonstration of the Kennet's bitmapped graphics). Users of the VTS Wordprocessing system may also recall another (text based) game called "Space", which was popular among the Logica developers (and probably also escaped into the wild).

Friday 25th July 2008
Charles Durrant (UK)


NAME  M4000
TYPE  Professional Computer
ORIGIN  United Kingdom
YEAR  198x
KEYBOARD  114 keys full stroke with numeric keypad
CPU  Intel 8086
SPEED  Unknown
RAM  Unknown
VRAM  Unknown
ROM  Unknown
COLORS  Amber monochrome
SOUND  Unknown
SIZE / WEIGHT  About 12kg
I/O PORTS  Unknown
BUILT IN MEDIA  2 x 5.25 inch or 3.5 inch (720 KB) floppy drives
OS  Concurrent CP/M-86, Concurrent DOS?
POWER SUPPLY  Power supply built-in
PRICE  Unknown

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