One Per Desk

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One Per Desk
Merlin Tonto
Also known asOPD
ManufacturerInternational Computers Limited (ICL)
Typepersonal computer
Release date1984; 37 years ago (1984)

The One Per Desk, or OPD, was an innovative hybrid personal computer/telecommunications terminal based on the hardware of the Sinclair QL.[1] The One Per Desk was built by International Computers Limited (ICL) and launched in the UK in 1984.[2] It was the result of a collaborative project between ICL, Sinclair Research and British Telecom begun in 1983,[3] originally intended to incorporate Sinclair's flat-screen CRT technology.

Rebadged versions of the OPD were sold in the United Kingdom as the Merlin Tonto[4] and in Australia as the Telecom Australia Computerphone.[5]


From the QL, the OPD borrowed the 68008 CPU, ZX8301/8302 ULAs, 128 KB of RAM and dual Microdrives (re-engineered by ICL for greater reliability) but not the 8049 Intelligent Peripheral Controller. Unique to the OPD was a "telephony module" incorporating an Intel 8051 microcontroller (which also controlled the keyboard), two PSTN lines and a V.21/V.23 modem, plus a built-in telephone handset and a TI TMS5220 speech synthesiser (for automatic answering of incoming calls).[6][7]

The OPD was supplied with either a 9-inch monochrome (white) monitor or a 14-inch colour monitor. Both monitors also housed the power supply for the OPD itself.

Later, 3.5" floppy disk drives were also available from third-party vendors.

ICL were the preferred supplier for UK local government, and OPDs found their way onto desks of council officers. Due to the cost, they tended to be issued only to the most senior, who were often elderly, had no interest in computers, and had secretaries to handle their administrative work, so many devices were simply used as telephones.


The system firmware (BFS or "Basic Functional Software") was unrelated to the QL's Qdos operating system, although a subset of SuperBASIC was provided on Microdrive cartridge. The BFS provided application-switching, voice/data call management, call answering, phone number directories, viewdata terminal emulation and a simple calculator.

The Psion applications suite bundled with the QL was also ported to the OPD as Xchange and was available as an optional ROM pack.

Other optional application software available on ROM included various terminal emulators such as Satellite Computing's ICL7561 emulator, plus their Action Diary and Presentation Software, address book, and inter-OPD communications utilities.[7]

An ICL supplied application was used to synchronise a national bingo game across hundreds of bingo halls in the UK. The integral V.23 dialup modem was used to provide remote communications to the central server.

Several UK ICL Mainframe (Series 39) customers, in Local Government and Ministry of Defence sectors, used statistics applications on OPD systems to view graphical representations of mainframe reports. Once again, the integral V.23 modem was used to download from the mainframe.

Merlin Tonto[edit]

British Telecom Business Systems sold the OPD as the Merlin M1800 Tonto.[8] BT intended the Tonto to be a centralised desktop information system able to access online services, mainframes and other similar systems through the BT telephone network. The Tonto retailed at £1,500 at launch. OPD peripherals and software ROM cartridges were also badged under the Merlin brand. BT withdrew support for the Tonto in February 1993. The name Tonto was derived from "The Outstanding New Telecoms Opportunity"[9]

Work on the Tonto influenced the design of a follow-on product by BT's Communications Terminal Products Group and Rathdown Industries known as the QWERTYphone, this aiming to provide the telephony features of the Tonto at "a much lower cost and in a more user-friendly manner".[10]


An enhanced version of the OPD was produced in small numbers for the United States market. This had a 68008FN CPU, 256 KB of RAM as standard, an RS-232 port and enhanced firmware.[11][12] The telephone answering function had a female voice, with a slight New Jersey accent.


  1. ^ The Register: Sinclair's FORGOTTEN Australia-only micro revealed!
  2. ^ Tebbutt, David (December 1984). "ICL OPD". Personal Computer World. pp. 120–124, 126. Retrieved 12 September 2020.
  3. ^ Holmes, S. P. (January 1987). "Merlin Tonto". British Telecommunications Engineering. 5 (4): 273–275. ISSN 0262-401X. Retrieved 26 February 2021.
  4. ^ "Tonto". British Telecommunications Engineering. 4 (1): 57. April 1985. ISSN 0262-401X. Retrieved 26 February 2021.
  5. ^ Tebbutt, David (January 1985). "ComputerPhone". Australian Personal Computer. pp. 14–16, 18, 23, 25–26. Retrieved 9 October 2020.
  6. ^ "ICL OPD — One Per Desk". OLD-COMPUTERS.COM. Retrieved 2008-04-23.
  7. ^ a b "A full technical breakdown of the OPD by Murray McCabe". Binary Dinosaurs. Retrieved 2008-04-23.
  8. ^ "Merlin Tonto". OLD-COMPUTERS.COM. Retrieved 2008-04-23.
  9. ^ "BT Merlin Tonto". Retrieved 25 November 2014.
  10. ^ Durkin, G. M. (January 1987). "QWERTYphone - A Low-Cost Integrated Voice/Data Terminal". British Telecommunications Engineering. 5 (4): 276–280. ISSN 0262-401X. Retrieved 26 February 2021.
  11. ^ "'Mega' OPD". Archived from the original on 2007-06-18. Retrieved 2008-04-23.
  12. ^ "MegaOPD unearthed". QUANTA. Archived from the original on 2008-08-21. Retrieved 2008-04-23.

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