BBC Micro: Encyclopedia - BBC Micro

BBC Micro

The BBC Micro, affectionately known as the Beeb, was an early home computer. It was designed and built by Acorn Computers Ltd for the British Broadcasting Corporation (BBC).

In the early 1980s, the BBC started what became known as the BBC Computer Literacy Project. The project was initiated largely in response to an extremely influential BBC documentary The Mighty Micro, in which Dr. Christopher Evans from the National Physical Laboratory predicted the coming (micro)computer revolution and its impact on the economy, industry and lifestyle of the United Kingdom.

BBC Micro - Background

The BBC wanted to base its project on a microcomputer capable of performing various tasks which they could then demonstrate in their TV series The Computer Programme (1981). The list of topics included programming, graphics, sound and music, Teletext, controlling external hardware, artificial intelligence etc. It decided to badge a micro, then drew up a fairly ambitious (for its time) specification and asked for takers.

The BBC discussed the issue with Sir Clive Sinclair, who tried to offer the unsuccessful Grundy NewBrain micro to them, but it came nowhere near the specification the BBC had drawn up, and was rejected. The BBC made appointments to see several other British computer manufacturers, including Dragon and Acorn.

The Acorn team had been working on an upgrade to their existing Atom microcomputer. Known as the Proton it included better graphics and a faster 2MHz MOS Technology 6502 CPU. The machine was only in prototype form at the time, but the Acorn team, which relied largely on Cambridge students (such as the legendary Roger Wilson and Steve Furber) worked through the night to get a working Proton together to show the BBC. The Acorn Proton was not only the only machine that came up to the BBC's specification, it also exceeded it in nearly every field. It was a clear winner.

It is rumoured that the BBC originally rejected the Proton, claiming that it did not portray the modern computer age correctly. Acorn countered this by submitting the Proton again, this time with the function keys painted a bright orange, and no other changes. It was accepted.

BBC Micro - Market impact

The machine was released as the BBC Microcomputer in early 1982. The machine was wildly popular in the UK; as with Sinclair's ZX Spectrum, also released around that time, demand greatly exceeded supply and for some months there were long delays before customers received the machines they had ordered. A brief attempt to market the machine in the United States failed, due largely to the dominance of the Apple II family. The success of the machine in the UK was largely due to its acceptance as an "educational" computer – the vast majority of UK schools used BBC Micros to teach computer literacy and information technology skills. Research Machines had, until this time, been one of the leaders in UK educational computer market. The BBC Micro was also a far more reliable and durable machine than Sinclair's ZX Spectrum, being able to cope with all the abuse that schoolchildren could throw at it.

The "Beeb", as it soon became known by its users, initially came in two models: the Model A and the Model B, initially priced at £235 and £335 respectively but rising almost immediately to £299 and £399 due to increased costs ([1]). Acorn anticipated the total sales to be around 12,000 units, but eventually more than 1 million BBC Micros were sold.

BBC Micro - Description

BBC Micro - Hardware features Models A and B

The Model A had 16 KB of user RAM; the Model B had 32 KB of user RAM. A particularly nice feature of the hardware was that the RAM was clocked at 4 MHz with alternating accesses given to the CPU and the video display circuits, giving a fully unified memory address structure with no speed penalties. Most competing micros with memory mapped display incured CPU speed penalties depending on the actions of the video circuits (e.g. the Amstrad CPC and to a lesser extent the ZX Spectrum) or kept video memory completely separate from the CPU address pool (e.g. the MSX).

The machine included a number of extra I/O interfaces: serial and parallel printer ports, an 8-bit I/O port, four analogue inputs and an expansion connector that enabled other hardware to be connected. Also an interface called the Tube allowed a second processor to be added; this was soon used in third-party add-ons, including a Zilog Z80 board and disk drive that allowed the BBC machine to run CP/M programs. Possibly the most well known software to run on the Tube was an enhanced version of Elite (see below). The Model A and the Model B were built on the same PCB and a Model A could be upgraded to a Model B without too much difficulty. Users wishing to run Model B software needed only to add the extra RAM and the user/printer 6522 VIA (which many games used for timers etc), a task which could be achieved without soldering. To do a full upgrade with all the external ports did however require soldering the connectors to the motherboard.

An apparent oversight in the manufacturing process resulted in a significant number of Model Bs producing a constant buzzing noise from the built-in speaker. This fault could be partly rectified by a soldering-capable person by carrying out certain amendments to the hardware.

BBC Micro - Software and expandability

Large numbers of games were written including the original version of the classic Elite (It has been suggested, but not verified, that the world's first networked multiplayer game was made for the BBC computer, a strategy wargame of some kind), and a wide range of hardware add-ons and expansions were available, as the machine had provision for floppy disk drives and networking hardware to be added; there were also sockets for the addition of extra ROM chips to the system. The built-in ROM-resident BBC BASIC programming language interpreter was by far the most sophisticated of its time, and wholly supported the machine's educational focus – quite advanced programs could be written without having to wade into the jungle of assembly language programming (necessary with many competing computers). Should one nevertheless want or need to do some assembly programming, BBC BASIC featured a built-in assembler.

BBC Micro - Successor machines and the retro scene

A cut-down version of the BBC Micro, intended more for game playing was the Acorn Electron (1983); games were written specially for the Electron's more limited hardware, but they could usually also be run on the BBC. Acorn introduced the Model B+ in 1984, increasing the total RAM to 64k and including floppy disk support as standard, but this had little market impact. In 1986, Acorn followed up with the BBC Master series, which offered 128KB memory and many other refinements which improved on the 1982 original. This attracted more interest and was the target of more software, although at heart it was essentially the same 6502-based BBC architecture, with many of the upgrades that the original design had intentionally made possible (extra ROM software, extra paged RAM, second processors) now included on the circuit board—a market stopgap while Acorn developed their 32-bit RISC project the Acorn Archimedes.

As of 2005, thanks to its ready expandability and I/O functions, there are still numbers of BBCs in use, and a retrocomputing community of dedicated users finding new things to do with the old hardware. The British Railway Network is believed to still use BBCs to drive the video departure boards on station platforms, and they still survive in a few interactive displays in museums across the country (often with no maintenance since they were first built). There are also a number of BBC Micro emulators for many OSes, so that even the original hardware is no longer necessary.

BBC Micro - Specifications

• 2 MHz MOS Technology 6502A processor (6512A in model B+)
• 32 KB ROM (16 KB MOS (Machine Operating System), 16 KB read-only paged space defaulting to the BBC BASIC EPROM)
• 32 KB RAM (16 KB in model A, 64 KB in model B+)
• Full-travel keyboard with a top row of ten red-orange function keys  f₀ − f₉
• Highly configurable graphics display based on the Motorola 6845. Eight graphics modes were provided by the system ROM:
  • Modes 0 to 6 could display a choice of colours from a palette of sixteen; the eight basic RGB colours (black, red, green, yellow, blue, magenta, cyan, white) and said colours in a flashing state;
  • Mode 7's Teletext capability was provided by a Mullard SAA5050 Teletext chip
    
    

• Four independent sound channels (one noise and 3 melodic) using the Texas Instruments SN76489 sound chip
• Built-in hardware support included:
  • pluggable ROMs, directly or via "Sideways" daughterboard
  • tape interface (with motor control), using a variation of the Kansas City standard data encoding scheme
  • Centronics parallel printer (model B only)
  • serial communication (using RS-423, a superset of RS-232)
  • display output for TV, RGB or 1v p-p video monitor
  • four analogue inputs (suitable for two joysticks)
  • proprietary "Tube" interface for external second CPU (options included a 3 MHz extra 6502, a Zilog Z80 for e.g. CP/M, an NS32016, an ARM1, and others)
  • a "user port" (model B only), and
  • generic expansion through the "1 MHz bus".
• Use of floppy disk drives required the installation of a DFS ROM (disk filing system) and a disk controller card based on the 8271 chip (later, and on the model B+, the WD1770)
• Via "The Tube" a second CPU could be attached (including a 3 MHz extra 6502, a Zilog Z80 for e.g. CP/M, an NS32016, an ARM1, and others)

• The default Model A/B motherboard could also be upgraded by adding the following components:
  • "Econet" large-scale low-cost networking system
  • ROM/RAM cartridge filing system via a slot to the left of the keyboard
  • speech synthesis hardware (Very few people bothered with this upgrade - the synthesiser was rather limited, and some games programmers succeeded in producing more versatile software speech synthesis using only the standard sound hardware)
  • Reset Button (It is doubtful if anyone ever added this, as a complete hardware reset can be accomplished by keyboard shortcuts at any time, even if the machine has crashed.)

The case was designed by industrial designer Allen Boothroyd of Cambridge Product Design Ltd. (Note that the photograph in this article is not coloured correctly - the machine was actually produced in a warm yellow/cream colour, as opposed to the sterile beige boxes favoured by other manufacturers. Somewhat amusingly, this also means collectors of BBC computers do not need to worry as much about the dreaded "yellowing" that plagues the aging plastic housings of many other machines.)

BBC Micro - Trivia

Musician Vince Clarke of the British synth pop bands Depeche Mode, Yazoo, and Erasure used a BBC Micro (and later a BBC Master) with UMI music sequencer to compose many hits. In music videos from the 1980s featuring Vince Clarke, a BBC Micro is often present or provides text and graphics such as the clip for Erasure's Oh L'Amour

In addition to Yazoo, also Queen used the UMI on their A Kind of Magic record. The UMI is also mentioned in the CD booklet. Other bands who have used the Beeb for making music are a-ha and the reggae band Steel Pulse .

See also

• Acorn Archimedes – the next generation BBC
• Risc PC – the next generation Archimedes
• Category:BBC Micro and Acorn Electron games

Adapted from the Wikipedia article "BBC Micro", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki