BBC Micro

The BBC Micro was, for much of the ’80s, the iconic educational computer in the UK. It was originally created by Acorn, a Cambridge firm, for the BBC’s Computer Literacy Project. This combined a hardware platform with a series of television programmes teaching programming. A range of pages on the BBC’s CEEFAX teletext service were devoted to distributing source code for the examples for this show. An external teletext decoder for the BBC allowed teletext pages to be loaded into the system: with a modem, the decoder could also be used to access British Telecom’s Prestel viewdata service.

Two models of the BBC, the Model A and Model B, were sold for £299 and £399 respectively: the Model A containing 16kB of RAM, and the Model B 32kB. Additional models of the original BBC containing more memory were later introduced, such as the B+ and B+128, with 64 and 128kB of RAM respectively.

The BBC had basic vector graphics capabilities and was commonly used with an implementation of Logo for teaching geometry. Logo was a dialect of Lisp designed for controlling a ‘turtle’ which would take commands like forward or backwards with a distance, or left or right with an angle. The turtle would travel over the screen drawing a line behind it, unless the ‘pen up’ command was delivered. In many schools, a physical turtle was used (although it often looked nothing like a turtle), which could draw shapes on a large sheet of paper.

Although Logo was often used for teaching, it was not supplied with the machine. When starting the machine, the user was presented with a prompt into which BBC BASIC code could be entered. This dialect of BASIC, designed by Sophie Wilson (then Roger Wilson) was designed to support structured programming, with named subroutines and other complex flow control structures. It also included an inline assembler, allowing 6502 assembly language to be interleaved with BASIC code, and for BASIC code to generate assembly allowing users to write compilers easily. The advanced features of BBC basic are credited as being one of the major reasons for Acorn winning the BBC contract, although their comparatively advanced hardware features are also likely to have been a significant factor.

The input/output (I/O) capabilities of the BBC made it popular in school technology labs years after the other capabilities of the machine had been superseded. A number of ports, including analogue input, were available and could easily be programmed from BASIC. These were used for controlling a variety of external devices, from seven-segment displays to robot arms. The systems could also be networked using Econet, Acorn’s proprietary networking interface.

Acorn later released two additional computers based on the BBC Micro design: the Acorn Electron and BBC Master. The Electron was essentially a low-end version of the BBC Micro, intended for use at home rather than school and designed to compete with the other low priced systems available at the time (e.g. the Sinclair Spectrum and Amstrad CPC464). The BBC Master, introduced in 1986, was an improved (and mostly backward-compatible) evolution of the original BBC design. The Master came with 128kB of RAM installed as standard. The software produced by the BBC’s Domesday Project was designed for the Master: to use the software, schools needed to purchase a videodisc player and trackball, which could be added to the Master using its expansion ports.

David Chisnall and Mark New

Further Reading: BBC interviews with the BBC’s creators