This website is an archived copy of "Chris's Acorns", now hosted by The Centre for Computing History as part of The Chris Whytehead collection.
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BBC Microcomputers

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When the BBC announced the Computer Literacy Project in 1981, a lot of people wanted more details. Here are 4 documents that were sent to people who wrote in for more details:

  1. BBC Computer Literacy Project Update  which outlines the BBC Microcomputer, its peripherals and upgrades.
  2. Hardware Specification
  3. BASIC outline
  4. BBC Microcomputer System Information Sheet G2 
  5. BBC Microcomputer with Added Processor and Teletext Adaptor   (3430K)

The BBC Micro went through many changes during its production life. These are not always easy to identify without access the the Acorn specifications. The early BBC Micros were built by a number of different suppliers including AB Electronics, Cleartone and ICL. These can be seen on the early serial numbers.

The 8-Bit Software  site has a very comprehensive descriptions of the different motherboards, keyboard, keystrips etc in Technical->Insides. It also has lots of other useful information on the 8 Bit Acorn computers, from the Atom to the Master.

Some companies (including Solidisk and Viglen) also produced alternative cases for the BBC Micro with the keyboard in 1 case and the motherboard and (optional) disc drives in the second case.

Manuals and documents

In addition to the manuals and documents available in Chris's Acorns Documents, many useful Acorn/BBC documents and manuals can be found at the BBC Documentation Project  although the site does not seem to have been updated recently.

Here is the original Acorn brochure for the BBC Micro:  AMP01 BBC Micro 
Here is a later A3 poster of the BBC Micro: APP16 BBC Micro 

 In January 1982 Practical Computing magazine published a review titled "BBC Micro" .

Here is the BBC Welcome Guide: BBCSoft_Welcome 

Here is the BBC Microcomputer Service Manual:  Acorn_BBCSMOct85 

The BBC Micro Computer User Guide is available in 4 versions:

I have not (yet) scanned any of them because they are 500+ pages and it takes too long. Copies are regularly auctioned on ebay. Alternatively they can be found from the BBC Documentation Project  under Essentials or BBC Lives under Acorn Essentials.

Here is the BBC Micro circuit diagram .

Acorn BBC Micro Upgrades

Acorn produced a range of 9 upgrades for the BBC Micro which were housed in a common case which was the same shape and about half the width of a BBC Micro, hence they are often know as "cheese wedges". They are:

  1. Teletext Adapter
  2. Prestel Adapter
  3. IEEE488 Interface
  4. Econet Bridge
  5. 6502 second processor
  6. Z80 second processor
  7. 32016 second processor (a.k.a. Cambridge Co-processor)
  8. Universal second processor unit
  9. ARM Evaluation Unit

Floppy Disc System

The BBC Micro could be upgraded with a Disc System, which consisted of:

In the BBC Model B+ the Intel 8271 Disc Controller was replaced by a Western Digital WD1770. Acorn also produced and 1770 Disc Interface Upgrade kit to upgrade BBC Micros. With the 1770 Disc interface fitted, the BBC Micro could be upgraded with the Advanced Disc Filing System ROM (see also Winchester Disc System).

The Acorn DFS was a sideways ROM which was fitted in one of the ROM sockets. There are several different versions but the main version is DFS 0.90 for the Intel 8271 and DFS 2.10 for the WD1770.

The floppy discs were single or double sided and 40 or 80 track giving:

Here is the Acorn product brochure for the BBC Micro Disc Storage: AMP03 BBC Micro Disc Storage

Here is the Acorn product brochure for the 1770 Disc Interface Upgrade kit.  
Here is the Acorn product brochure for the ADFS Upgrade .

Here is the 1770 Disc InterfaceUpgrade Kit Fitting Instructions. 

Here is the Disc System User Guide (1982).   Acorn_DiscSystemUG
Here is the Disc Filing System User Guide 1983 with addendum for the 1770 DFS.

Here is the ADFS User Guide. 

Apart from Acorn, many third parties supplied floppy disc drives for the BBC Micro and Master, some also supplied their own DFS (e.g. Cumana, Opus, Solidisk and Watford Electronics) and a few produced their own disc controllers (See 8 bit Upgrades ).

Winchester Disc System

The BBC Micro could be upgraded with the Acorn Winchester Disc System which was a 10 MB or 30 MB Winchester hard disc and a new filing system, the Winchester Disc Filing System (which was later renamed ADFS). The Winchester disc connected to the 1 MHz bus and the ADFS ROM installed in one of the sideways ROM sockets.

Here is the Acorn product brochure for the Winchester Disc System:APP32 Winchester Disc System

Here is the Acorn Winchester Disc Filing System User GuideAcorn Winchester Disc Filing System User Guide

Apart from Acorn, third parties such as Cumana, Opus, Solidisk, Technomatic and Watford Electronics produced Winchester discs systems for the BBC Micro and Master. 

Speech System

The BBC Micro could be upgraded with a Speech System. This was based on the Texas Instruments TMS5220 Voice Synthesis Processor. This uses a phrase database is a PHROM to contain the sounds. Acorn used Kenneth Kendal's voice to pronounce the words.

Here is the Speech upgrade instructions. 

Here is the Speech System User Guide.Acorn_SpeechSystemUG 

BBC Microcomputer Models

The BBC Micro models are:

  1. Proton (the prototype)
  2. BBC Model A
  3. BBC Model B
  4. Hong Kong BBC Model B
  5. BBC Model B+
  6. German & US BBC Model Bs 
  7. SCL Unicorn Microcomputer 
  8. Solidisk cased BBC Microcomputer 

Differences between Model A and Model B

To keep the price down Acorn frequently omitted non-essential components from their computers, these were then available as upgrades. The Model A lacked:

But the biggest limitation on the Model A was only having 16K RAM, which was also shared with the screen memory. This meant that the model A could not display graphics modes 0, 1, 2 & 3. 16K RAM was also a serious constraint on program size.

The following upgrades were available for both the Model A and the Model B:

Differences between Issues

The BBC micro motherboard is the same for the Model A and Model B, but there were different 7 Issues and there were also case and keyboard changes. The changes to the circuit design are listed in seciton 5.3 of the BBC Microcomputer Service Manual. The issues are:


 The Proton was a prototype for Acorn's next computer after the Atom. When the BBC announced the contract for the computer to accompany their forthcoming Computer Literacy program. Acorn hurriedly completed the proton and demonstrated it to the BBC. They won the contract, hence the BBC Micro!.
I wonder if any Protons actually exist any more. Possible hidden in the attic/garage of an ex-Acorn employee, only to be discovered at a house clearance sale! [Wanted]

 BBC Model A

Acorn released 2 different BBC Model A products:

  1. ANA01 - Model A
  2. ANA02 - Model A with Econet interface 

 It is hard to find a genuine model A which has not been upgraded, partially or totally, to model B specification. In 2004, one was sold on ebay for £370, but in 2003 two were sold for around £80.

Here are pictures and descriptions of:

 BBC Model B

 Acorn released 4 different BBC Model B products:

  1. ANB01 - Model B
  2. ANB02 - Model B with Econet interface
  3. ANB03 - Model B with disc interface
  4. ANB04 - Model B with Disc and Econet interfaces

Here are pictures and descriptions of:

Hong Kong BBC Model B

Acorn increased manufacturing capacity, in the face of the unexpected success of the BBC Micro, by assembling BBC Micros in Hong Kong. Wong Electronics did the assembly. The only model I know about is:

  1. B01 - Model B

Here are pictures and the description of:

BBC Model B+

The BBC Model B+64K was launched in 1984 to extend the life of the aging BBC Micro. It has an additional 32K RAM to improve on the limited 32K of the original BBC micro using techniques pioneered by various 3rd party add-ins. The additional 32K is divided into 12K shadow memory and 20K sideways memory. The Model B+ also includes the 1770 DFS disc interface instead of the 8271 and has an extra 2 ROM sockets.

  1. ANB51 - BBC Model B+64K
  2. ANB52 - BBC Model B+64K with Econet
  3. ANB53 - BBC Model B+64K with Disc interface
  4. ANB54 - BBC Model B+64K with Disc and Econet interfaces
  5. ANB55 - BBC Model B+128K

Here are pictures and descriptions of:

BBC Micro German and US versions

As far as I know there are only 2 model of the BBC Micro build for non-UK markets, they are:

  1. GNB14 - German BBC Model B
  2. UNB09 - US BBC Model B

Here are pictures and descriptions:

SCL Unicorn Microcomputer

SCL in India made a version of the BBC Microcomputer which was called the Unicorn Microcomputer.
Here pictures and descriptions:

Solidisk cased BBC Microcomputer

Solidisk produces a two box CPU and Keyboard case for the BBC Micro. Any model could be used with this case. This esxmple is a BBC Model B Issue 3.
Here are some pictures: