support the exchange of forms, letters and memos. 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". 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. The hardware specifications of the M2105, observed from manufactured units, include the 6502 CPU (SY6502 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. The speech synthesis was used for the "voice response" function which answered incoming voice calls by playing a synthesised message to the caller. 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, although this particular composition of RAM is apparently contradicted by the RAM devices present on surviving M2105 machines. 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. Technical information Much of the core functionality of the BBC Micro the video and memory controller, cassette input/output, timers and sound generation was replicated using a single customised ULA chip designed by Acorn in conjunction with Ferranti, albeit with only one sound channel instead of three (and one noise channel), and without the character-based Teletext Mode 7. The edge connector on the rear of the Electron exposes all address and data bus lines from the CPU, including the upper eight bits of the address bus, in contrast to the limited selection available via the BBC Micro's expansion ports, with the One Megahertz Bus as the principal mechanism for general purpose expansion on the BBC Micro only providing the lower eight bits of the address bus. In addition, various control signals provided by the CPU and ULA are exposed