BBC Micro

BBC Micro

Infobox computer
Name = BBC Model A to Model B+128

Photo =
Caption = The original BBC Micro
Type = 8-bit microcomputer
Developer = Acorn Computers
Released = Late 1981
Discontinued = 1986
Processor = MOS Technology 6502/6512 at 2 MHz
Memory = 16 KiB - 128 KiB
Media = Cassette tape, floppy disk
Graphics = 640×256, 16 colours (framebuffer)
78×75, 8 colours (Teletext)
Display = PAL/NTSC, RF/composite/TTL RGB
Input = 4× analogue, 10× digital, keyboard, light pen port
Connectivity = RS-423 serial, parallel, Econet, 1 MHz bus, Tube coprocessor interface
OS = Acorn MOS
Baseprice = £299 (in 1981)
The BBC Microcomputer System, or BBC Micro, was a series of microcomputers and associated peripherals designed and built by Acorn Computers, for the "BBC Computer Literacy Project" operated by the British Broadcasting Corporation. Designed with an emphasis on education it was notable for its ruggedness, expandability and the quality of its operating system.

The "Acorn Proton" was a pre-existing project at Acorn to succeed the Atom home computer. It was then submitted for, and won, the Literacy Project tender for a computer to accompany the TV programmes and literature. Renamed the BBC Micro, the platform was chosen by most schools and became a cornerstone of computing in British education in the 1980s, changing Acorn's fortunes. It was also moderately successful as a home computer in the United Kingdom despite its high cost. The machine was directly involved in the development of the ARM architecture which sees widespread use in embedded systems as of 2008.

While twelve models were eventually produced with the BBC brand, the term "BBC Micro" is usually colloquially used to refer to the first four (Model A, B, B+64 and B+128), with the later eight models referred to as the BBC Master and Archimedes series.


In the early 1980s, the BBC started what became known as the "BBC Computer Literacy Project". The project was initiated partly in responsecite web | last =Hormby | first =Thomas | title =Acorn and the BBC Micro: From education to obscurity | work =Low End Mac | date =2007-02-08 | url = | format =HTML | doi = | accessdate =2007-03-01] to an extremely influential ITV documentary series "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.

The BBC wanted to base its project on a microcomputer capable of performing various tasks which they could then demonstrate in their 1981 TV series "The Computer Programme". The list of topics included programming, graphics, sound and music, Teletext, controlling external hardware and artificial intelligence. 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 offered the NewBrain micro to them, but it was rejected. The BBC made appointments to see several other British computer manufacturers, including Dragon and Acorn.

The Acorn team had already 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, largely made up of students including Sophie Wilson and Steve Furber, worked through the night to get a working Proton together to show the BBCCitation | last =Collins | first =Barry | author-link = | last2 = | first2 = | author2-link = | title =BBC Basic: the people's language | newspaper =PC Pro | pages = | year = | date =2006-08-07 | accessdate =2007-02-07 | url = ] . The Acorn Proton not only was the only machine to come up to the BBC's specification, but also exceeded it in nearly every parameter.

Market impact

The machine was released as the BBC Microcomputer in late 1981 and became affectionately known as the "Beeb". The machine was popular in the UK, especially in the educational market. As with Sinclair's ZX Spectrum, also released later in 1982, demand greatly exceeded supply. 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. 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. Some Commonwealth countries, like India, started their own Computer Literacy programs and used the BBC Micro [cite news | last = Tank | first = Andrew | title = India's Schoolchildren Have Got Class | work = Computer Weekly | pages =29 | publisher = General Reference Center Gold | date = 1986-04-10 ] .
Research Machines had, until this time, been one of the leaders in UK educational computer market. One of the main advantages which helped the BBC Micro in the educational market was its durable construction. The machine's casing and keyboard was solidly built compared to that of the ZX Spectrum, being able to cope with all the abuse that schoolchildren could throw at it.

The Model A and the Model B were initially priced at £235 and £335 respectively, but rising almost immediately to £299 and £399 due to increased costs [ [ Stairwaytohell.Com - Hardware ] ] . Acorn anticipated the total sales to be around 12,000 units, but eventually more than 1.5 million BBC Micros were sold [ [ BBC NEWS | Technology | Home computing pioneer honoured ] ] .

The cost of the BBC Models was high compared to competitors such as the ZX Spectrum and in 1983, Acorn attempted to counter this by producing a largely compatible but cut down version intended for game playing, the 32K Acorn Electron. Games written specially for the Electron's more limited hardware could usually also be run on the Model B.


Hardware features, Models A and B

The Model A had 16 KB (16 KiB) of user RAM; the Model B had 32 KB of user RAM. A feature that the Micro shared with other 6502 computers such as the Apple and the early Commodore models 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).

The machine included a number of extra I/O interfaces: serial and parallel printer ports; an 8-bit general purpose digital I/O port; a port offering four analogue inputs, a light pen input, and switch inputs; and an expansion connector (the "1 MHz bus") that enabled other hardware to be connected. Extra ROMs could be fitted (four on the PCB or sixteen with expansion hardware) and accessed via paged memory. An Econet network interface and a disk drive interface were available as options; all motherboards had space for the electronic components, but Econet was rarely fitted. Additionally, an Acorn proprietary interface called the "Tube" allowed a second processor to be added; several types of processor were offered by Acorn including 68000 versions. It was later used in third-party add-ons, including a Zilog Z80 board and disk drive that allowed the BBC machine to run CP/M programs.

The Tube interface allowed Acorn to use ARM CPU equipped BBC Micros as software development tools when creating the Acorn Archimedes. This resulted in the ARM development kit for the BBC Micro in 1986, priced at around £4000 [ [ The start of the revival - The ARM and the Archimedes (1986 to 1988) ] ] . In 2006 a kit with an ARM7TDMI CPU running at 64 MHz, with 16MB of RAM was released for the BBC Micro and Master, using the Tube interface to turn the old 8 bit micros into 32 bit RISC machines just as Acorn had done two decades previously [ [ BBC Micro ARM7 co-processor available - RISC OS News, Software and Information ] ] . Among the software titles to run on the Tube were 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) 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.

Early BBC Micros used linear power supplies at the insistence of the BBC's engineering specification, but these very hot running PSUs were soon replaced in production by switched mode units.

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 soldering a resistor across two pads [ [ Sprow's webpages - cyber doctor for poorly beebs ] ] .

Export models

Two export models were developed; one for the UScite web
title= USA model BBC micro
accessdate= 2008-03-28
last= Scholten
first= Wouter
date= 2007-06-17
] , with Econet and speech hardware as standard; the other for the Federal Republic of Germanycite web
title= Chris's Acorns: German BBC Microcomputer Model B
accessdate= 2008-03-28
last= Whytehead
first= Chris
date= 2007-11-09
] . Both were fitted with RF shielding as required by the respective countries, and they were still based on the Intel 8271 floppy drive controller. From June 1983 the name was always spelled out in full – "British Broadcasting Corporation Microcomputer System" – to avoid confusion with Brown, Boveri & Cie in international markets.cite journal | year = 1983 | month = June | title = Name changes for the worse | journal = The Micro User | volume = 1 | issue = 4 | pages = 112 | publisher = Database Publications | location = Stockport, UK | issn = 0265-4040]

US models included BASIC III, modified to accept the American spelling of COLOR, however the height of the graphics display was reduced from 256 scan lines per field to 200 to suit NTSC TVscite book
last= Bray
first= Andrew C.
coauthors= Dickens, Adrian C.; Holmes, Mark A.
title= The Advanced User Guide for the BBC Microcomputer
format= zipped PDF
accessdate= 2008-03-28
year= 1983
publisher= Cambridge Microcomputer Centre
location= Cambridge, UK
isbn= 0946827001
pages= 512
chapter= Appendix G
] , seriously affecting applications written for British computers. After the failed US marketing campaign the frustrated machines were remanufactured for the British market and [ off] , resulting in a third 'export' variant.cite web
title= Chris's Acorns: US BBC Microcomputer (converted for UK)
accessdate= 2008-03-28
last= Whytehead
first= Chris

Hardware features: B+64 and B+128

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 B+128 came with an additional 64 KB ( 4 × 16 KB "Sideways" RAM banks) to give a total RAM of 128 KB.

The new B+ was incapable of running some original BBC B programs and games, such as, for example, the very popular "Castle Quest". A particular problem was the replacement of the Intel 8271 floppy disk controller with the Western Digital 1770 — not only was the new controller mapped to different addresses, it was fundamentally incompatible and the many 8271 emulators that did exist were necessarily imperfect for all but basic operationcite journal | author = Kevin Edwards | year = 1986 | month = January | title = Inside the 8271 – how your DFS really functions | journal = The Micro User | volume = 3 | issue = 11 | pages = 228 | publisher = Database Publications | location = Stockport, UK | issn = 0265-4040] . A piece of software that used copy protection techniques which involved direct access to the controller, simply wouldn't run on the new system.

There was also a long-running problem late on in the B/B+'s life infamous amongst B+ owners, when Superior Software released "Repton Infinity", which refused to run on the B+. A string of unsuccessful replacements were issued before one compatible with both was finally released.

Software and expandability

The BBC Micro platform amassed a large software base of games and educational titles, reflecting its dual niches at home and in the classroom. Notable examples of each include "Elite" (the game's original release) and Granny's Garden. Programming languages and some applications were supplied on ROM chips to be installed on the motherboard. These could be loaded instantly and left the main RAM free for programs or documents.

Although appropriate content was little-supported by television broadcasters, telesoftware could be downloaded via the optional Teletext Adapter and the third-party teletext adaptors that emerged.

The built-in operating system, Acorn MOS, provided an extensive API to interface with all standard peripherals, ROM-based software and the screenAcorn Computers Ltd, "The BBC Microcomputer System User Guide", chapter 43-44.
The light pen, 1 MHz bus and user port were supported by generic memory-mapped I/O calls ("OSBYTE" 146-151), and Teletext graphics could be printed through "OSWRCH" like normal text. The Archimedes and its Interface Podule successfully emulated Teletext and the user port through these calls.] . Features like vector graphics, keyboard macros, cursor-based editing, sound queues and envelopes, normally private to BASIC, were made available to any application. BASIC itself, being in a separate ROM, could be replaced with any equivalent language.

Acorn strongly discouraged programmers from directly accessing the hardware and system variables, favouring official API calls [Acorn Computers Ltd, "The BBC Microcomputer System User Guide", chapters 43, 46.] . This was ostensibly to make sure programs kept working when moved to the Tube coprocessor, but it also made BBC Micro software more portable across the Acorn range. Whereas untrappable PEEKs and POKEs were commonly used on other computers to reach the system elements [Sinclair Research Ltd,"ZX Spectrum BASIC programming", chapters 23-25] , both BBC BASIC and assembly language programs could set up the CPU registers or a parameter block, and call an operating system routine. In this way the MOS could translate the request for the devices and memory layout of the local machine (especially the Electron and Archimedes) or send it across the Tube interface, as direct access was impossible from the coprocessor.

As the early BBC Micros had ample I/O allowing machines to be interconnected, and as many schools and universities employed the machines in Econet networks, numerous networked multiplayer games were created. With the exception of a tank game, "Bolo", few rose to popularity; in no small measure due to the limited number of machines aggregated in one place. A relatively late but well documented example can be found in a dissertation based on a ringed RS-423 interconnect [ [ Bolo Cambridge Dissertation ] ] .


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 resorting to unstructured programming or machine code (necessary with many competing computers). Should one want or need to do some assembly programming, BBC BASIC featured a built-in assembler.

When the BBC Micro was released, many competing home computers used Microsoft BASIC, or variants typically designed to resemble it. Compared to Microsoft BASIC, BBC BASIC supported IF…THEN…ELSE, named procedures and functions, but retained GOTO and GOSUB for compatibility. It also supported high-resolution graphics, four-channel sound, pointer-based memory access (borrowed from BCPL) and rudimentary macro assembly, albeit with clumsy syntax for each. Long variable names were accepted and distinguished completely, not just by the first two characters.

Successor machines and the retro scene

In 1986, Acorn followed up with the BBC Master series, which offered memory sizes from 128 KB and many other refinements which improved on the 1981 original, 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 or as internal plug-in modules.

However, Acorn had produced their own 32-bit RISC CPU in 1985, the ARM2 and were working on building a personal computer around it. This was released in 1987 as four models in the Archimedes series, with the lower-specified two models (with 512 KB and 1 MiB respectively) released as BBC Microcomputers. Although the Archimedes ultimately was not a major success, the ARM family of processors has gone on to become the dominant processor architecture in mobile embedded consumer devices, particularly mobile phones.

The last model, the BBC A3000, was released in 1989 as essentially a 1 MiB Archimedes back in a single case form factor.

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. A BBC B+ was observed running the communications link in an unattended water pumping station in Oxhey in 1995. They still survive in a few interactive displays in museums across the country, and Jodrell Bank was reported to still be using a BBC Micro to steer its 42ft radio telescope in 2004 [The Register: "My PC is older than yours", [] ] . There are also a number of BBC Micro emulators for many OSes, so that even the original hardware is no longer necessary.

In March 2008, the creators of the BBC Micro met at the Science Museum in London. The museum plans to hold an exhibition about the computer and its legacy in 2009 [cite web|title='Beeb' creators reunite at museum|url=|publisher=BBC News Online|date=2008-03-20|accessdate=2008-03-23] .

Specifications (Model A to Model B+128)

The case was designed by industrial designer Allen Boothroyd of Cambridge Product Design Ltd. [cite web |title=Underside of Issue 1 BBC Micro |date=2007-01-08 |url=|accessdate=2008-01-29]

Display modes

Like the IBM PC with the contemporary Color Graphics Adapter, the video output of the BBC Micro could be switched under software control between a number of display modes. These varied between 20 column text suitable for a domestic TV, to 80 column text best viewed with a high-quality monitor. The variety of modes offered applications a flexible compromise between colour depth, resolution and memory footprint: in the first models, the OS and applications used whatever RAM was left over from the display.

Mode 7 was a Teletext mode, extremely economical on memory and an original requirement due to the BBC's own use of broadcast teletext (Ceefax): it also made the computer useful as a Prestel terminal. Train time displays at UK stations were driven by BBC Master computers until around the late 1990s.

colour cube, and eight flashing colours made by alternating the basic colour with its inverse. The palette could be freely reprogrammed without touching display memory. Modes 3 and 6 were special text-only modes that used less RAM by reducing the number of text rows and inserting blank scan lines below each row. Mode 6 was the same size as Teletext but could show diacritics and user defined characters. All the other ASCII modes supported vector graphics.

The BBC B+ and the later Master allowed 'shadow modes', where the framebuffer was stored in 20 KB of an alternative RAM bank, leaving the main memory up to 0x8000 free for user programs. This feature was enabled by setting bit 7 of the mode variable, i.e. by requesting modes 128–135.

Optional extras

A speech synthesis upgrade based on the Texas Instruments TMS5220 featured sampled phonemes spoken by BBC newscaster Kenneth Kendall and provided a socket next to the keyboard for serial ROM cartridges to be plugged in. The upgrade was standard on the US model where it had an American vocabulary. Elsewhere it sold poorly and was eventually eclipsed by Superior Software's software-based synthesiser using the standard sound hardware.

Use in the entertainment industry

* 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 hitsCitation | title =Erasure's Big Hit | newspaper =Acorn User | year =1988 | date =1988-06-01 ] . 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 record "A Kind of Magic ". 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.
* Numerous 80s episodes of "Doctor Who" feature text, graphics, and sound effects generated by a BBC Micro computer. Such episodes include "The Five Doctors" (first broadcast in 1983) and "The Twin Dilemma" (first broadcast in 1984).
* During the 80s and 90s a BBC Micro was used on the television programme "Mastermind" to display the contestants' scores.

See also

* BBC Master
* Acorn Archimedes
* Risc PC
* Richard T. Russell
* Prism Micro Products


External links

* [ Page documenting the history of the BBC micro and other related computers]
* [ BeebWiki] — BBC Micro Wiki
* [ Acorn and the BBC Micro: From education to obscurity]

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