and cassette interface card were the same cards as used the System 1, but with the keypad and LED display of the latter left unused. The system could be expanded with any of Acorn's standard Eurocards to add further functionality. In 1982 it was being offered for £320, or £480 with power supply, plus an additional £136 for the optional keyboard. System 3 The Acorn System 3 added a floppy disk controller card, floppy disk drive, and disk operating system ROM, replacing the cassette interface card and cassette operating system of the System 2 machine. The System 3 became the standard workhorse for development in the Acorn lab: the Acorn Atom has been called a cut-down version of the System 3; and it was based on the System 3 that much of the development work for the BBC Micro was done. A minimum configuration contained: A CPU card A 40×25 Teletext-standard VDU card 8K RAM with 4K BASIC ROM A floppy disk controller One 100K floppy disk drive In 1982 this was being offered for £775, or £1075 with power supply, casing, and two further 8K RAM cards; plus, again, an additional £136 for a keyboard. System 4 The Acorn System 4 was similar to the System 3, but in a double height frame, containing fourteen slots in the lower frame, and two floppy disk drives in the upper half of the frame above them. With casing, power supply, and a basic 16K of RAM it was being offered for £1525 in 1982 (again, plus extra for the keyboard). System 5 The Acorn System 5 was the final Acorn rack-mounted system, released in 1983. It was mounted in an extra-height single 19-inch frame, which could accommodate two vertically mounted 5 1/4-inch floppy drives, with either seven or ten Eurocard slots. It came complete with a power supply, and was only available fully assembled. As standard it had a 1 MHz 6502, 32K DRAM, a disk controller, and either the 80×25 or the Teletext 40×25 VDU cards. Customers could choose which cards to install in the remaining slots, including interface cards, an additional 16K DRAM card, and/or an Econet network adapter; they could also choose to upgrade the processor board to a faster 2 MHz 6502 board. References External links The Acorn Atom pre-history Acorn System Computers System 2 6502-based home computers Computers designed in the United Kingdom