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The BBC Microcomputer System (BBC Micro)

 

Although I never owned a BBC Micro in the '80s, I had thought about acquiring one for a while, and when one come up on my local  Freegle (it's like FreeRycle), I couldn't resist it. This is the first 6502 based computer that I have owned - there's nothing like keeping up with technology eh? Unfortunately, I have too many other things on the go at the moment to devote much time to the "Beeb" or to create much content here, this page will have to do, until I find some more time.

 

A Brief History of the BBC Micro

Background

Dr Christopher Evans was a British computer scientist and author who, in 1979, wrote a book which attempted to predict the effects that the forthcoming computing revolution would have on the UK's economy, industry and lifestyle. The book was called "The Mighty Micro - The impact of the computer Revolution", published in hardback by Victor Gollancz Ltd, (ISBN 0-575-02708-8), it was reprinted in paperback by Coronet Books in November 1980 (ISBN-10: 0-340-25975-2, ISBN-13: 978-0340259757), if you are interested in seeing how well (or badly) his predictions turned out, you can pick up a used copy pretty cheaply from Amazon.

Evans scripted and presented a six part TV documentary series of the same name for Associated Television (ATV) which was broadcast by ITV between October and December 1979. Sadly, the series was broadcast posthumously, Evans having died from cancer in the early October. The documentary was very influential, with questions even being asked in parliament.

In response to the ITV series, the BBC launched their Computer Literacy Project, with the stated aim of introducing "interested adults to the world of computers and computing, and to provide the opportunity for viewers to learn through direct experience how to program and use a microcomputer."

The Department of Industry (DoI) became interested in the Project, as did BBC Enterprises, which saw an opportunity to sell a machine to go with the series. BBC Engineering was instructed to draw up an objective specification for a suitable microcomputer around which to base a TV programme.

You can read the full synopsis of the Computer Literacy Project in this document, which describes how "the project is built around a 10 part television series...".  The first episode of The Computer Programme was broadcast on 11th January 1982. The programmes were presented by Ian McNaught-Davis and Chris Serle, each 25 minute programme covered various topics from BASIC programming to simple robotics and control. Kraftwerk provided the theme tune, taken from their 1981 track Computer World, and the series was followed up by two more: Making the most of the Micro in 1983 and Micro Live from 1984 to 1987. If you would like to revisit The Computer Programme, the complete series has been uploaded to YouTube by Jess Zafra

Computer Selection

The Department of Industry was obviously keen that the computer to be used in the Project be of UK manufacture and put pressure on the BBC to ensure that was the case. In the light of this, the BBC specification was written very much around the NewBrain computer, a product of Newbury Laboratories. Newbury was owned by the National Enterprise Board (NEB), set up by the Labour government to increase public ownership in industry. The NEB was also part owner of Sinclair Radionics where the idea for the NewBrain computer was conceived, before the Project was moved to Newbury.

Despite the NewBrain being the favoured computer, it lost out to  Acorn Computers who offered the Proton which was to become the BBC Micro. The Wikipedia entry for Acorn Computers has a some interesting details on how Acorn won, or rather how Newbury didn't win, the contract for the BBC Micro, which was eventually released on 1st December 1981. There is also a very interesting blog here that offers one view of the selection process for the BBC Micro, and another here, that discusses Clive Sinclair's reaction to the final choice.

The BBC Micro

As a result of this support from the government and the publicly owned BBC, the machine became very popular in the UK, especially in the educational market where about 80 per cent of British schools had a BBC microcomputer.

In order to satisfy demand, the BBC Micros were built by a number of different suppliers. According to Acorn User issue 1 - July/Aug 1982: "Acorn currently use two manufacturing plants in the UK. ICL at Kidsgrove are largely responsible for manufacturing the model B and Cleartone in Gwent for model A computers. Cleartone have recently been taken over by AB Electronics. A third UK plant is starting production of both models this month."

Other manufacturers included BSR (UK), Astec, Keltek.

My Model B, Serial Number 189011, was built by AB Electronic Systems Ltd.

Specifications - Model B

Processor  MOS Technology 6502
CPU Clock Speed 2 MHz

In common with some other 6502 machines, the RAM was clocked twice as fast as the CPU (4 MHz) with alternating access given to the CPU and the video display circuits.

ROM 32 kB of ROM composed of a 16 kB MOS (Machine Operating System) chip, and 16 kB read-only paged space defaulting to the BBC BASIC chip. Four paged 16 kB ROM sockets standard, expandable to 16.
RAM - fitted  32 KBytes
RAM - maximum  32 KBytes
Display  

Graphics

Mode

Resolution X x Y

Hardware

Colours

Video RAM

Used (KB)

Screen

Type

Char Cells Pixels
0 80 32 640 256 2 20 Graphics
1 40 32 320 256 4 20 Graphics
2 20 32 160 256 8 20 Graphics
3 80 25 640 200 2 16 Text
4 40 32 320 256 2 10 Graphics
5 20 32 160 256 4 10 Graphics
6 40 25 320 200 2 8 Text

7

(Teletext)

40 25  480 500 8 1 Text
Colours  16 logical colours
Video Output 6-pin DIN digital RGB connector +5 V/0 V, - with pin-out as shown

1 V p-p composite colour or monochrome video (link S39)

Built-in UHF (PAL) RF modulator

Sound Four independent sound channels (one noise and three melodic) using the Texas Instruments SN76489 sound chip. Phoneme-based speech synthesis using the Texas Instruments TMS5220 with a custom Acorn ROM (the "PHROM", a TMS6100) of Kenneth Kendall's voice (optional).
I/O Capability 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,  Cassette Interface (operating at1200 or 300 Baud) with Motor Control.

The "Tube" interface allowed a second processor to be fitted, including a Z80 allowing CP/M programs to be run.

Data Storage

Cassette Tape

Floppy Disk Drive (Optional)

Built in languages  BBC BASIC - Read about its history from the developer, Richard Russell

See how BBC BASIC compared against competitor machines of the time when running PCW Benchmark tests here.

Construction

73 Key full-travel keyboard with a top row of ten red-orange user definable function keys 09.

The keyboard has two key rollover and auto repeat.

Secondary power output Power supply for external disk drives, 6-pin, top to bottom, left to right: 0V, 0V +5V DC @1.25A, +12V DC @1.25A, NC, -5V DC @75mA,

 

Specifications - Model A

The Model A had the same specifications above, with the exceptions that it had only 16KBytes of RAM and was missing the following features:-
  • RGB port
  • Serial port
  • Analogue port
  • Tube Interface
  • User port
  • Centronics Printer port
  • 1MHz bus.

 

 

Some Useful BBC Computer Resources on the Web
StarDot Community site for Acorn Computers: Atom, BBC Micro, Electron and Archimedes
Retrokit Paul Vernon's site, lots of useful information about his collection of Acorn hardware
Stairwaytohell BBC Micro and Electron Games Archive
8-Bit Software The BBC and Master Computer Public Domain Library, also has complete scans of Acorn User Mags.
BeebWiki 8-bit Acorn Computer Wiki articles relating to the Acorn BBC Microcomputer and related computers
Chris's Acorns A comprehensive site dedicated to the complete range of Acorn Computers, including the BBC Micro.
(Now hosted by the Centre for Computing History in Cambridge, UK)
RetroClinic Home of DataCentre - an upgrade for the BBC Micro, with USB, Compact Flash, IDE & RAM
BeebControl A good website for interfacing the the BBC Micro
The BBC Lives! Enthusiasts site for Acorn Computers
BeebMaster Another Beeb enthusiast, good source of technical info and stocks some BBC spares & upgrades
   

 

   
Wikipedia BBC Micro entry on Wikipedia
Old Computers Website dedicated to, yes, old computers
   

 

 

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