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BBC Micro

From Academic Kids

Top view of the BBC Micro
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Top view of the 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 UK National Physical Laboratory predicted the coming (micro)computer revolution and its impact on the economy, industry and lifestyle of the United Kingdom.

Contents

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 peddle 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.

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 at 235, and the Model B at 335. Acorn anticipated the total sales to be around 12,000 units, but eventually more than 1 million BBC Micros were sold.

Description

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 4MHz 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. 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.

Large numbers of games were written including the original version of the classic Elite, 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.

As of 2005, thanks to its ready expandability and I/O functions, there are still numbers of BBCs in use, and a community of dedicated users finding new things to do with the old hardware. There are also a number of BBC Micro emulators for many OSes, so that even the original hardware is no longer necessary.

A cut-down version of the BBC Micro, intended more for game playing was the Acorn Electron; games were written specially for the Electron's more limited hardware, but they could also be run on the BBC. In 1986, Acorn followed the B model up with the BBC Master, which offered 128KB memory and many other refinements which improved on the 1982 original.

The case was designed by industrial designer Allen Boothroyd of Cambridge Product Design Ltd.

Specifications

  • 2 MHz MOS Technology 6502 processor
  • 32 KB ROM (16 KB MOS (Machine Operating System), 16 KB BBC BASIC)
  • 32 KB RAM (16 KB in model A, 64 KB in model B+)
  • Eight different graphics modes, with varying resolutions and numbers of colours, hence varying memory requirements (see table below)
  • 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" daughter board
    • tape interface (with motor control)
    • 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 CPU expansion
    • 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
  • 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)
  • Highly configurable graphics display based on the Motorola 6845. Modes provided by the system ROM (pixel and char. resolutions given as columns X × lines Y):
Mode Pixel res. Chars Colours Memory
0 640 × 256 80 × 32 2 20 KB
1 320 × 256 40 × 32 4 20 KB
2 160 × 256 20 × 32 16 20 KB
3 80 × 25 2 16 KB
4 320 × 256 40 × 32 2 10 KB
5 160 × 256 20 × 32 4 10 KB
6 40 × 25 2 8 KB
7 Teletext 40 × 25 8 1 KB
  • Modes 0 to 6 could display a choice of colours from a palette of sixteen; the eight RGB colours (black, red, green, yellow, blue, magenta, cyan, white) and eight flashing colours
  • Mode seven's Teletext capability was provided by a Mullard SAA5050 Teletext chip

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.

See also

External links


de:BBC Micro

it:BBC Micro

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