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 Cristopher 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.

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 2 MHz 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 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 (the original specification called for a Z80 CPU running CP/M ^*). 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.

Market impact

The machine was released as the BBC Microcomputer in late 1981. 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 BBC Micro 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 (^*). Acorn anticipated the total sales to be around 12,000 units, but eventually more than 1 million BBC Micros were sold.

Description

Hardware features, Models A and B

The Model A had 16 KB of user RAM; the Model B had 32 KB of user RAM. One particularly nice feature of the hardware was that the RAM was clocked twice as fast as the CPU (4 MHz), with alternating access given to the CPU and the video display circuits. This gave the BBC Micro a fully unified memory address structure with no speed penalties. Most competing micros with memory mapped display incurred 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). Another benefit of this approach was that the video cycling automatically ensured the refresh of the RAM.

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) and a CAD package which required a second 6502 cpu and a 5 dimensional joystick called a "Bitstick". 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) and snip a link, 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.

Software and expandability

Large numbers of games were written for the Beeb, including the original version of the classic Elite. A range of hardware add-ons and expansions was available, and the machine had provisions for floppy disk drives and networking hardware. There were also sockets for the addition of extra ROM chips. 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. Advanced programs could be written without having to wade into the jungle of assembly language programming (necessary with many competing computers). Should one want, or need, to do some assembly programming, BBC BASIC featured a built-in assembler.

As the early BBC micros had ample I/O allowing machines to be interconnected, and as most schools and universities employed the machines in an 'Econet', numerous networked multiplayer games were created. With the exception of a Nethack game and a tank game (Bolo, for example), few rose to popularity; in no small measure due to the limited number of machines aggregated in one place. It has been suggested, but not verified, that the world's first networked multiplayer game was written for the BBC computer, a strategy wargame of some kind. A relatively late but well documented example can be found in this dissertation based on a ringed RS423 interconnect.

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 mid 1985, increasing the total RAM to 64 KB and including floppy disk support as standard, but this had modest market impact. The extra RAM in the Model B+ BBC Micro was assigned as two blocks, a block of 20 kB dedicated solely for screen display (so-called "Shadow" RAM) and a block of 12 kB of 'special' Sideways RAM. The much-needed memory increase provided by this new 1985 'Beeb' was a welcome development, but was seen as an eighteen months or so too late to challenge the increased specifications of new rival microcomputer systems. Acorn also sold a version of the B+ with an addition 64 kB ( 4 × 16 kB "Sideways" RAM banks) to give a total RAM of 128 kB.

In 1986, Acorn followed up with the BBC Master series, which offered 128 kB memory and many other refinements which improved on the 1981 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.

Specifications

2 MHz MOS Technology 6502A processor (6512A in model B+)
32 KB ROM (48 KB in model B+ due to the presence by default of the WD1770 disk filing system 16 KB "DFS" 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 $f_0-f_9$
Highly configurable graphics display based on the Motorola 6845 CRTC. Eight graphics modes were provided by the system ROM:
- Modes 0 to 6 could display a choice of colours from a logical palette of sixteen, though only eight colours were available; the eight basic RGB colours (0-black, 1-red, 2-green, 3-yellow, 4-blue, 5-magenta, 6-cyan, 7-white) and eight colours in a flashing state, (8-black/white, 9-red/cyan, 10-green/magenta, 11-yellow/blue, 12-blue/yellow, 13-magenta/green, 14-cyan/red, 15-white/black)
- Mode 7's Teletext capability was provided by a Mullard SAA5050 Teletext chip

{| class="wikitable" Graphics mode Resolution (X×Y) Hardware colours Video RAM
used (KB) Char cells Pixels 0 80 × 32 640 × 256 2 20 1 40 × 32 320 × 256 4 20 2 20 × 32 160 × 256 8 20 3 80 × 25 – 2 16 4 40 × 32 320 × 256 2 10 5 20 × 32 160 × 256 4 10 6 40 × 25 – 2 8 7 40 × 25 Teletext 80 × 75 8 1

Four independent sound channels (one noise and 3 melodic) using the Texas Instruments SN76489 sound chip
Built-in hardware support included:
- Sideways (paged) 8K or 16K ROMs (of which the BBC BASIC ROM was the only one supplied by default): up to 16 were supported by the OS but only 4 by the standard hardware. Add-on boards were made by a variety of companies to allow use of the full 16.
- Tape interface (with a relay operated motor control), using a variation of the Kansas City standard data encoding scheme running at 1200 or 300 baud
- 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, colour or monochrome (link S38)
- A DB15 pin with four 12 bit analogue inputs (suitable for two joysticks), two inputs suitable for pushbuttons and an input for a light pen
- 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 16 pin IDC style "user port" (not in model A, by default) with 8 general purpose digital I/O pins and two special/trigger sensitive digital pins
- generic expansion through the "1 MHz bus"
Use of floppy disc drives required the installation of a DFS ROM (disk filing system) and a disk controller card based on the Intel 8271 chip (later, and on the model B+ (as standard), the WD1770 AND WD1772)
Via "The Tube" a second CPU could be attached (including a 3 MHz extra 6502, 4MHZ WDC65C102, a 4MHz 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 - around 100Kbit/s using the Motorola 6854 - standard on US model
- Serial ROM cartridge filing system via a slot to the left of the keyboard - usually fitted as part of the Speech Upgrade
- Speech synthesis hardware based around the Texas Instruments TMS5220 - standard on US model. (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 pressing BREAK on the keyboard at any time, even if the machine has crashed.)

The case was designed by industrial designer Allen Boothroyd of Cambridge Product Design Ltd. The machine was produced in a warm yellow/cream colour, in contrast to the sterile beige boxes favoured by other manufacturers. Somewhat amusingly, this means collectors of BBC computers do not need to worry as much about the dreaded "yellowing" that plagues the ageing plastic housings of many other machines. They do go yellow, hence the nickname "rhubarb and custard" for sadly aged Beebs on eBay.

Trivia

The BBC Domesday Project, a pioneering multimedia experiment, was based on a modified version of the BBC Micro's successor the BBC Master.

Musician Vince Clarke of the British synth pop bands Depeche Mode, Yazoo, and Erasure used a BBC Micro (and later a BBC Master) with the 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.

Queen used the UMI Music Sequencer 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.

The BBC Micro provided in-game graphics for the BBC TV show "The Adventure Game", where the BREAK key on the keyboard was covered by a plastic box to prevent accidental pressing.

The opening sequence to series 1 of the BBC spoof comedy TV show "Look Around You" (8 × 10 minute episodes) featured a BBC Micro, running a rudimentary BASIC program.

In 1984–87, Ken Webster in Dodleston, UK, purported to be in contact with someone called Tomas Harden from the 16th century, along with other characters including some claiming to be from the future, one of them being known as 2109 (or 2105). The messages are purported to have been left — somehow through the space-time continuum — on a humble BBC Model B fitted with an Acorn DFS upgrade. They were found on the editing screen of the ROM-based word processor EDWORD and within EDWORD files created on disk (or appended to them). Ken detailed the curious case in his now out-of-print book The Vertical Plane Grafton Books, ISBN 0-586-20476-8, two episodes of a BBC 1 documentary series presented by Carol Vorderman Of This World, [http://open.bbc.co.uk/catalogue/infax/programme/LFEI405S 20 August 1996 & 27 August 1996 and in a Fortean Times article, The Vertical Plane - FT108.

External links

Acorn Computers | Home computers | BBC

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