---
title: Merlin M4000
categories:
- Computers
types:
- Professional Computer
origins:
- United Kingdom
cpus:
- Intel 8086
params:
  name: M4000
  image: /media/museum/photos/bt_merlin_m4000_1s.jpg
  company: /companies/merlin
  company_name: Merlin
  specs:
  - label: NAME
    value: M4000
  - label: MANUFACTURER
    value: Merlin
  - label: TYPE
    value: Professional Computer
  - label: ORIGIN
    value: United Kingdom
  - label: YEAR
    value: 198x
  - label: BUILT IN LANGUAGE
    value: None
  - label: KEYBOARD
    value: 114 keys full stroke with numeric keypad
  - label: CPU
    value: Intel 8086
  - label: SPEED
    value: Unknown
  - label: RAM
    value: Unknown
  - label: VRAM
    value: Unknown
  - label: ROM
    value: Unknown
  - label: TEXT MODES
    value: Unknown
  - label: GRAPHIC MODES
    value: Unknown
  - label: COLORS
    value: Amber monochrome
  - label: SOUND
    value: Unknown
  - label: SIZE / WEIGHT
    value: About 12kg
  - label: I/O PORTS
    value: Unknown
  - label: BUILT IN MEDIA
    value: 2 x 5.25 inch or 3.5 inch (720 KB) floppy drives
  - label: OS
    value: Concurrent CP/M-86, Concurrent DOS?
  - label: POWER SUPPLY
    value: Power supply built-in
  - label: PERIPHERALS
    value: Unknown
  - label: PRICE
    value: Unknown
  tabs:
  - photos
  forum_thread: 1225
  photos:
  - title: M4000
    subtitle: ''
    text: Thanks to Riaz Sobrany for this picture
    image: /media/museum/photos/bt_merlin_m4000_1.jpg
  oc_id: 1258
  source:
    url: https://web.archive.org/web/20230318004515/http://www.old-computers.com/museum/computer.asp?c=1258
    date: '2023-03-18'
---

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](/museum/merlin-tonto/) which is a rebadged [ICL OPD](/museum/icl-opd-one-per-desk/).

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 !

<table> <tr> <td></td> <td>We need more info about this computer ! If you designed, used, or have more info about this system, please send us pictures or anything you might find useful.</td> <td></td> </tr> </table>