BBC Micro

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Home * Hardware * BBC Micro

BBC Micro [1]

BBC Micro, (BBC Microcomputer System)
a series of 8-bit 6502 based home computers by Acorn Computers Ltd, initially designed by a team including Steve Furber and Sophie Wilson, first released in December 1981. The Micro was contracted by the British Broadcasting Corporation (BBC) after a call for bids for a computer to accompany the TV series and literature for their Computer Literacy Project [2] [3] [4], which was won by Acorn with the Proton, a successor of the Acorn Atom - renamed the BBC Micro. Acorn also employed the machine to simulate and develop the ARM architecture which, many years later, has become hugely successful [5].


The BBC Micro had a 6502 processor running at full 2 MHz speed, accessing fast DRAM, alternating concurrently with the MC6845 video display controller, featuring eight display modes for text and graphics varied between 20 and 40-column text suitable for a TV, to 80-column text requiring an RGB-connected video monitor. As noted by Steve Furber in a recent interview [6], the alternating fast 4 MHz RAM access required some address multiplexing using exactly the 81LS95 tri-state octal buffer [7] from National Semiconductor - for unknown reasons, 81LS95 from other vendors were not working. Multiple input/output ports were available to connect with peripherals or other machines, such as serial PS-423 ports, parallel ports, analogue input ports with ADC for instance used by a joystick, light pen input, an expansion connector (the "1 MHz bus") to expand the system with additional hardware such as the BBC Micro expansion, and the Tube interface to connect a secondary processor. The BBC Micro had an integrated keyboard and a cassette interface. Floppy disks were optional through the Intel 8271 programmable floppy disk controller, in later models replaced by Western Digital's FD1771. The Texas Instruments SN76489 was responsible for sound. Phoneme based speech synthesis using TI's TMS5220 speech chip with a custom Acorn ROM of Kenneth Kendall's voice was optional [8].


The initial BBC Micro was shipped as Model A with 16 KiB of user RAM, and Model B with 32 KiB. The Acorn Electron was a budget version of the B-Model released by Acorn in 1983. Two export models were developed for the US [9] and West Germany in 1983 [10]. As a sideline, the Acorn Business Computer (ABC) range of machines was announced in October 1984 [11]. The Model B+ in mid 1985, increased the total RAM to 64 KiB, the B+128 came with an additional 64 KiB (4 × 16 KBi "Sideways" RAM banks) to give a total RAM of 128 KiB [12]. The BBC Master with integrated floppies followed in 1986 with an enhanced 65SC12 CPU, and expandable 128 KiB RAM as default, and remained in production until 1993 [13].


The Acorn Machine Operating System (MOS) was held in 16 KiB of ROM on the motherboard. A further 16 KiB ROM contained the BBC BASIC interpreter. Acornsoft was the major publisher of software for the BBC Micro and Acorn Electron, who released Acornsoft Chess written by Arthur Norman and Nick Pelling. Other British companies in the fast growing software market were Micro Power , Computer Concepts, Ltd. and Bug-Byte.

Chess Programs

First Computer Go Tournament

The BBC Micro Go Tournament was held in London, on January 7 and 8, 1984, sponsored by Acornsoft. All eight programs ran on BBC Micro. The Go playing program by Bronyslaw Przybla won the event [14].

See also




Circuit Diagram (pdf)

Forum Posts

those good old times... in the 70-80ties by Thorsten Czub, CCC, May 06, 2002

External Links

BBC Micro


Chess Programs

Computer Literacy Project



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