Acorn Electron

The Electron was able to save and load programs onto audio cassette via a supplied cable that connected it to any standard tape recorder that had the correct sockets. It was capable of bitmapped graphics, and could use either a television set, a colour (RGB) monitor or a monochrome monitor as its display. Several expansions were made available to provide many of the capabilities omitted from the BBC Micro. Acorn introduced a general-purpose expansion unit, the Plus 1, offering analogue joystick and parallel ports, together with cartridge slots into which ROM cartridges, providing software, or other kinds of hardware expansions, such as disc interfaces, could be inserted.^[4] Acorn also produced a dedicated disc expansion, the Plus 3, featuring a disc controller and 3.5-inch floppy drive.^[5]


For a short period, the Electron was reportedly the best selling micro in the United Kingdom,^[6] with an estimated 200,000^[7] to 250,000 machines^[8] sold over its entire commercial lifespan. With production effectively discontinued by Acorn as early as 1985,^[9] and with the machine offered in bundles with games and expansions, later being substantially discounted by retailers, a revival in demand for the Electron supported a market for software and expansions without Acorn's involvement,^[10] with its market for games also helping to sustain the continued viability of games production for the BBC Micro.^[11]

Merlin M2105[edit]

An unusual variant of the Electron was sold by British Telecom Business Systems as the BT Merlin M2105 Communications Terminal, being previewed by British Telecom at the Communications '84 show.^[165] This consisted of a rebadged Electron plus a large expansion unit containing 32 KB of battery-backed RAM (making up 64 KB of RAM in total), up to 64 KB of ROM resident in four sockets (making up to 96 KB of ROM in total), a Centronics printer port, an RS423 serial port, a modem, and the speech generator previously offered for the BBC Micro.^[52] The ROM firmware provided dial-up communications facilities, text editing and text messaging functions. The complete product included a monitor and dot-matrix printer.^[166]


Initially trialled in a six-month pilot at 50 florists, with the intention of rolling out to all 2,500 members of the UK network,^[166] these were used by the Interflora florists network in the UK for over a decade.^[167][168] Used mostly for sending messages, despite providing support for other applications, limited availability of the product led Interflora to look for alternatives after five years, although users appeared to be happy with the product as it was.^[169]


This generic product combination of the Electron and accompanying expansion was apparently known as the Chain during development,^[52] itself having a different board layout,^[170] with British Telecom having intended the M2105 to be a product supporting access to an online service known as Healthnet.^[52][171] This service aimed to improve and speed up communications within hospitals so that patients could be treated and discharged more quickly, and to facilitate transfers of information to doctors and health workers outside hospitals, with communications taking place over conventional telephone lines. The service was to be introduced in the Hammersmith and Fulham district health authority, with installation starting at Charing Cross Hospital. The Electron was said to be particularly suitable for deployment in this application in that it had a "large expansion bus",^[172] ostensibly making the machine amenable to the necessary adaptations required for the role, together with its "price, and the fact it has a real keyboard".^[173] As a Healthnet terminal, the M2105 was intended to support the exchange of forms, letters and memos.^[174]


The adoption of an Acorn product in this role was perhaps also unusual in that much of BT's Merlin range of this era had been supplied by ICL, notably the M2226 small business computer and M3300 "communicating word processor".^[175][176] Nevertheless, the M2105 offered interoperability with other BT products such as the QWERTYphone which was able to receive messages from the M2105 and the Merlin Tonto.^[177]: 280


The hardware specifications of the M2105, observed from manufactured units, include the 6502 CPU (SY6502^[178] or R6502), ULA and 32 KB of dynamic RAM fitted in the Electron main unit, plus 32 KB of static RAM, two 6522 VIA devices for interfacing, AM2910PC modem, SCN2681A UART, and TMS5220 plus TMS6100 for speech synthesis.^[168] The speech synthesis was used for the "voice response" function which answered incoming voice calls by playing a synthesised message to the caller.^[179] The components chosen and the capabilities provided (excluding speech synthesis) are broadly similar to those featured by the Acorn Communicator which was another product of Acorn's custom systems division.


The product documentation indicates a specification with 48 KB of RAM plus 16 KB of "non volatile CMOS RAM" and 96 KB of ROM,^[179]: 87 although this particular composition of RAM is apparently contradicted by the RAM devices present on surviving M2105 machines.^[180] However, the earlier Chain variant of the board does appear to provide only 16 KB of static RAM using two HM6264LP-15 chips, also providing an extra 16 KB of dynamic RAM using eight MK4516-15 chips, suggesting that the product evolved during development.^[170]