BBC Micro

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File:BBC owl.png
The BBC Micro owl logo
File:Master512 small.jpg
The BBC Master 512
It became the standard computer in British schools, and a whole generation of British schoolchildren was reared on BBC Micros, and I often bump into people who say this was my first computer, and at that time it also made Britain the most computer-literate nation in the world; we had more computers in schools than any other nation."
Hermann Hauser, Acorn co-founder[1]

The British Broadcasting Corporation Microcomputer System, in the form of the Model A, Model B, Model B+ and Master Series, was the main hardware product of Acorn Computers during much of the 1980s. BBC Micro is the accepted abbreviated name for any of the Acorn computers in this series based on the 6502 family of processors and bearing the name of the BBC. In its various forms the BBC Micro was produced from 1981 at the earliest to 1994, when Acorn finally ceased production of the Master Series. The history of the BBC Micro is complex and its role in the evolution of computing is of great significance.


Early history

The BBC Micro was the product of the BBC's Computer Literacy Project, an early 1980s initiative designed to educate the British public in anticipation of the emerging home microcomputer age. In 1980, the idea of a new television series to front the campaign was pitched among BBC executives, educational and government departments. Support was found from most involved, and it was decided to specify a particular microcomputer to be sold as part of the project.

Finalizing the specifications, including resolving important questions such as the choice of processor and default language, took some time for the BBC to work out, and it was not long before several British computer manufacturers were attempting to win the lucrative contract to produce the 'BBC Microcomputer'. At first Newbury and Sinclair both seemed front runners to design and make the system, which originally was to run the CP/M Z80 operating system. The abortive attempt by Newbury to propose such a computer led to the specification being changed to favour a 6502-based system.

This change afforded Acorn Computers a sudden advantage, as at the time they had been working on a replacement to their fairly successful 6502-based Atom called the Proton, which was already fairly close to the new BBC specification. After a period of fevered work at Acorn to add the additional required components, the Proton was demonstrated to the BBC and ultimately accepted as the core design for the BBC Microcomputer. Production began in earnest in 1981 with a target release date of early 1982.[2]

Model A/B


The first BBC Micros were the Models A and B, released with much fanfare in early 1982. Powered by a 2Mhz 6502A processor and with 16K and 32K of memory respectively, at the time the capabilities of the Model B far exceeded what most other 8-bit microcomputers were capable of. Both models came supplied with a fully fledged Machine Operating System and BBC BASIC, the enhanced version of the BASIC language that included support for advanced programming structures and a built-in 6502 assembler.

Early models were marked as 'BBC Microcomputer' on the perspex keyboard strip - this, however, led to a trademark dispute with Brown Boveri Coporation, and the badges were changed to read 'British Broadcasting Corporation' instead.

All BBC Micros were capable of storing and loading data on tape via the cassete interface, but the Model B was also available fitted with an Econet interface (ANB02) additional 8271 floppy disc interface (ANB03) and with both disc and Econet interfaces (ANB04). Options on the Model A were by default limited to tape-only (ANA01) or Econet (ANA02).

The Model B's number of I/O and interfacing options was unmatched and some of the possibilities were near revolutionary for an 8-bit microcomputer of the day. Options comprised a cassette interface, RS-423 serial port, advanced analogue interface, floppy disc drive connector, parallel printer port, memory-mapped user port, 1Mhz bus interface, the Tube connector for high-speed communication with a Second Processor, a choice of RF, composite and RGB video output, and the contemporarily significant option of an Econet network interface. The Model A lacked most of these options bar Econet due to being built without the necessary connectors and some of the required components.

The BBC Micro's increased capabilities over the competition were mirrored in the fact that it was more expensive than other 8-bit micros at the time, with the Models A and B retailing for £235 and £335. Due to the costs of production these prices had to be swiftly raised to £299 and £399 respectively. Acorn had expected the cheaper Model A to be the more successful machine in the popular market, with the Model B selling in smaller quantities to more professional users. They were proved wrong, however, in that the Model A was largely percieved as a limited model not worth the £100 saving over its fully capable brother and sold fewer than the Model B. In addition to the fact that a Model A could be upgraded to a Model B at any time by any Acorn dealer at a cost of around £125, this is reflected in the fact that it is not easy to find a Model A without any upgrades or modifications.

The original BBC Micro was well recieved and represented by far Acorn's biggest success up to this point. Due to the unique marketing style, the system's flexibility, the availability of Econet and most of all a programme of educational discounts, the computer enjoyed its biggest success in the educational and professional sector, with BBC Micros installed in their thousands in almost every school in Britain. This rise to dominance in the educational market was to have great influence on Acorn during and even after the BBC Micro era. Nonetheless, the system also had impact on the home market.

While commercial software for the BBC Micro was slow to come at first, Acorn's own Acornsoft label soon spearheaded its rapid uptake for software development. Due to the system's history, image and user base, a massive library of educational software (including 'edutainment' such as Granny's Garden as well as interfacing programs for the control of LOGO turtles and other peripherals) and professional applications such as View and Wordwise represented a significant part of the BBC's catalogue during the Model B era. Despite this, it also became home to plenty of beloved games, including Chuckie Egg, Exile, Imogen and most famously Elite.

Model B+


The Model B+ was released in 1984 as a refinement of the original Model B's design. Acorn slightly redesigned the motherboard and fitted at first 64K and later 128K RAM (via a rather haphazardly fitted additional daughterboard). The most notable change was the ROM sockets, which were moved from their inconvenient position under the keyboard to the upper left of the motherboard. The MOS was updated, noticeably displaying 'Acorn OS' in the place of 'BBC Computer' in the startup message

The Model B+ was essentially a stop-gap machine to bridge the gap between the Model B and the coming Master Series. While the B+ did certainly offer a few worthwhile improvements to the Model B's design it still had all the hallmarks of mutton dressed as lamb, including the cheap-looking stickers applied to dress up later 128K models. The market was apparently unimpressed as the B+ did not sell in the quantities of the earlier models.

Master Series

Master 128


The BBC Master Series Microcomputer was first released in 1986 as a true replacement for the Model B. Acorn took the chance to fully redesign the hardware in order to address some of the flaws of the original BBC Micro design. On the outside, the most obvious changes were the extension of the case to accomodate a numeric keypad and a pair of cartridge slots, into which cartridges hosting ROMs could be fitted without taking the computer apart.

The more important changes were under the lid, however. The Master Series came with both 128K of RAM and the Acorn 1770 DFS as standard in the base Master 128 model. Sideways RAM support was also built into the system. New connectors on the motherboard allowed the attachment of an internal Second Processor to the Tube (the Tube host code was also included by default) and the solderless fitting of an integrated Econet module. The MOS was revised and the addition of a battery-backed CMOS allowed certain boot settings to be saved while the computer was switched off. BASIC was updated to version 4. The Master was also supplied with Acornsoft's View word processor and Viewsheet spreadsheet (previously available separately for the Model B) and the Terminal and Edit utilities in ROM. In addition there were various minor graphics enhancements and bug fixes.

In spite of these refinements, the core BBC Micro architecture remained the same. The Master offered comprehensive backward compatibility with most software and hardware made for earlier models, maintaining a cassette interface and all other I/O interfaces of the Model B, including the external Tube connector. This allowed users an instant library of tried-and-tested additions to the Master.

Master Compact


The Master Compact was added to the Master Series in 1986, not long after the release of the Master 128. Essentially it aimed to redress the impression of many home users of the BBC Micro as a prohibitively professional (and prohibitively expensive) computer by targeting the home market. The Compact was supplied complete with 3½" disc drive and monitor so as to make a ready-to-go home computer package.

Many features were removed or changed in order to shrink the case to compact proportions and lower the cost. The ROM cartridge slots, Tube, 1Mhz bus, user port, RF output and cassette interface were removed, with the serial port relegated to an optional upgrade. Meanwhile the joystick, printer and disc connectors were changed to sockets incompatible with other BBC Micro peripherals. By default, the only supported filing system was ADFS.

Ultimately these changes were the Master Compact's undoing as the removal of the cassette and 5¼" floppy interfaces severely restricted the amount of existing software that could be used with the Compact, since 3½" floppies were still relatively new, more expensive and less common than the 5¼" discs associated with the rest of the Master Series. Consequently the Master Compact was not as popular as the rest of the BBC Micro range and was not the success that Acorn had hoped.

Other models

As well as the basic Master 128 model, Acorn also released several variants to cater for particular fields of endeavour. The Master 512 included an internal 80186 Co-Processor with 512K of onboard RAM. This was capable of running some x86 MS-DOS applications and came with the DOS-Plus OS and GEM graphical office suite complete with mouse.

The Master Turbo is a Master 128 fitted with an internal 65C102 Co-Processor which was aimed at the high performance market as it could execute many programs at close to double speed. The Master AIV or Domesday System, which was the key hardware component in the Domesday Project, consisted of a Master Turbo fitted with an internal SCSI interface to interface with a laserdisc player containing the Domesday laserdiscs.

The Master ET (Econet Terminal) was a cut-down 'thin client' Master designed for use in conjunction with an Econet system. It omitted the disc, cassette and most I/O connections bar Econet in order to reduce costs in the manner of the Model A.

A further model, the Master Scientific, presumably designed for laboratory work and including an internal 32016 Co-Processor is reported to have been planned, but this system was apparently never produced.

Derivative systems

Final years

As the BBC Computer Literacy Project became more and more a memory of the distant past the BBC association became less valuable to Acorn. In addition the 6502, as an 8-bit processor, was becoming seriously dated as processors with larger word widths capable of addressing far more memory were rapidly encroaching on the home market, leading to Acorn designing their own Acorn Risc Machine architecture that was to power the Archimedes series.

Early Archimedes systems did still carry the BBC Microcomputer legend and owl logo but are not properly considered BBC Micros due to the architectural and OS differences. Despite the Archimedes line gradually becoming Acorn's main focus, production of the Master 128 did not cease until 1994, a moment that marks the final retirement of the BBC Micro brand.