1980s Vintage Computers

Acorn BBC Computers

Master 128 base unit

Acorn was selected in 1981 by the British Broadcasting Corporation to manufacture a computer with Basic for homes and schools. This was part of a tie-in with the TV series 'The Computer Programme' and the aim was 10,000 computers in the first year. The resulting computer (the BBC A and BBC B) was far more successful than anticipated, and Acorn went on to become a major UK computer company for the remainder of the 1980s.

BBC A / BBC B

The BBC A was the original machine, featuring a cassette interface, 16K of RAM, 32K of ROM and cost 299. The BBC B was more powerful with 32K of RAM and built in tube, 1MHz bus and serial interfaces and cost 399. A disk interface using the 8271 controller with the Acorn Disk Filing System (DFS) was available for £120, this provided support for single density / FM disks only. Out-of-the box the BBC computer could run BASIC programs, and came with a tutorial-style User Guide which encouraged users to learn the features of the language stage by stage. The BBC B was very common in the UK, largely due to its take up by education authorities who overall bought many hundred thousand so that nearly every primary and secondary school had at least one. Similarly at home many enthusiasts caught on to the strengths of the BBC B and they sold well, but at a price at the high-end compared to say a Sinclair Spectrum. Several businesses bought them, sometimes as a general purpose computer, and sometimes because of the technical specification and ease of expansion. By the late 1990s every school had PCs and so most of the old BBC Bs became available and were either scrapped, given away or sold. Nowadays they are easily available at car boot sales, on eBay or in local papers.

The specification of the the BBC B was very advanced compared to similar home computers:

  • 6502 8-bit processor running at 2MHz.
  • 32K RAM (expansion RAM available via paging in a 16K area).
  • 32K ROM as standard, including a powerful 16K BASIC,  with sockets for 4 additional 16K ROMs (accessible via paging).
  • Range of monochrome and colour video modes (text in 20, 40 or 80 columns, 25 or 32 rows, and graphics from 640x256 to 160x256). 
  • Three video connectors  (composite, RGB and UHF).
  • High-quality keyboard.
  • System bus expansion sockets (1MHz and Tube).
  • Parallel and serial (RS423) interfaces.
  • Analogue and digital input / output ports.
  • Cassette tape interface.
  • 4 channel sound.

The standard options that could be built into the BBC B included:

  • Floppy and hard disk interfaces (for external drives).
  • Network interface (Econet).
  • Speech synthesizer.

Acorn developed a range of external modules in the same design as the BBC B, these included:

  • A  6502 second processor (a 65SC02 running at 3MHz with its own 64K RAM).
  • A Z80 second processor (running at 4MHz with 64KB of RAM), principally to support CP/M.
  • A Teletext adapter, to receive text and programs via TV broadcasts.
  • A Prestel Adapter, a modem, which together with software, gave access to dial-up videotext.
  • An IEEE 488 interface.

The second processor options allowed bigger programs to run, and also allowed the base unit to run graphics at maximum resolution with out using up system RAM or affecting program performance.

BBC B+

This machine was similar in looks to the BBC B, but provided either 64K or 128K of RAM. It came with a floppy disk interface included using a newer 1770 controller, thus adding support for double density / MFM disks. However it was launched with DFS so was limited to single density, until Acorn brought out ADFS which added double density support. The service manual states the B+ supports the same 8271 controller as the original BBC B for backwards compatibility.

The BBC B+ featured a 6512 processor which had the same op-codes as the 6502. The computer was introduced in 1985 for £499 but was not sufficiently better than a BBC B and so was not a great seller.

BBC Master

By 1985 the BBC B was lagging behind its competitors, so Acorn launched the Master as an enhanced series of machines, featuring a faster processor, far more memory, and a better keyboard. Crucially the Master was largely backwards compatible with software and expansion modules from the earlier BBC B machine.

The Master series was an-round improvement on the BBC B and was very popular. The basic machine in the range was the Master 128 (pictured at the top of this article), which as the name suggests has 128KB of RAM, and also 128KB of ROM. The ROM software include the View word-processor, a ViewSheet spreadsheet and two disk filing system ROMS (DFS and ADFS), as well as BBC BASIC. The Master's features include:

  • 65SC12 processor running at 2MHz. This included 8 additional op-codes to the 6502 and improved performance.
  • Enhanced keyboard with a separate numeric pad.
  • More integration on the motherboard leading to fewer ICs.
  • A real-time clock, plus configuration stored in battery-backed RAM.  
  • Additional Tube interface, allowing both external and internal co-processors.
  • Floppy disk controller (WD1770).
  • Two slots for ROM cartridges.

I also have a Master 512. This is a Master 128 fitted with a plug-in 80186 co-processor board with its own 512K of RAM (hence the name, although the machine actually has 640K of RAM in total!). This allows 16-bit software to be run, and was supplied with DR DOS+ and the GEM graphical desktop (with mouse support). My Master 512 was further enhanced by its previous owner with a Solidisk PC Plus board, which plugs into the 80186 board (making 3 layers in total). This contains a further 512K of RAM, but due to the need for I/O and ROM it reports 896K free. I have downloaded the DOS+ and GEM software from Yellow Pig which work fine.

There was also a Master Turbo, which like the Master 512 was a Master 128 plus a built in co-processor board, this time a 65C102 with its own 64K of RAM. This processor has 12 additional op-codes to the 6502, and at 4MHz it ran twice as fast as a BBC B. This meant that nearly all BBC 6502 based code could be run on the co-processor, but it ran much faster than on any other machine in the family, making this system the most desirable of them all. 

The other machines in the range were:

  • Master Compact, which featured a base unit with floppy drives and a smaller keyboard unit.
  • Master Scientific, included a 32016 internal co-processor board.
  • Master Econet station, a cut-down machine for use on an Econet network.
  • Master AIV (Domesday machine), based on a Master Turbo, with a SCSI interface to a Philips LaserDisk player, used in particular for the UK 1986 Domesday project.

Acorn then developed the Archimedes range of machines that used faster ARM processors and far larger memory with a graphical user interface, but also run BBC BASIC and so so again were popular with schools.

Acorn BBC Tips


This page was last revised on: 03/06/08