The BBC Computer Literacy Project - The BBC Micro (1981).

The BBC Microcomputer is perhaps the best known of all Acorn's computers. The design was originally developed during 1980 under the name Proton. Acorn had decided to stick with the 6502 processor as the basis for the new machine but, in an attempt to mininise the risk associated with making a bad choice, developed an interface port that allowed the simple connection of a second processor.

Around this time the BBC were launching their Computer Literacy Project, and were looking for a machine to link it with. An outline specification was sent out to a number of manufacturers, including Acorn, Sinclair and Dragon. The outline specification matched the specification Acorn had developed for the Proton, and the BBC arranged to come and see the machine in operation. The only problem was that the machine didn't at that time exist. The meeting had been arranged on a Monday for the following Friday - Curry and Hauser, assisted by Steve Furbur and Roger Wilson, spent Monday, Tuesday and Wednesday assembling the machine, and the first test took place on the Wedneday evening, and the machine didn't work. Finally, at 7am on Friday morning, it was found that the problem was due to timing differences between the prototype machine and the development kit. The meeting with the BBC took place at 10am, and the people from the BBC were impressed with what they saw and awarded Acorn a contract for 12,000 machines. The Proton was renamed the BBC Microcomputer.

To enable the BBC Micro to be so fast, a large amount of the computer circuity was bundled up in to two Uncommitted Logic Arrays (ULAs), of which 10,000 were ordered from Ferranti. When the completed chips were delivered, it turned out that only 3%, those at the top end of the specified speed range, would work. Fortunately, Ferranti were able to manufacture new versions and get the revised chips back to Acorn in just three days.

Initially two versions of the BBC Micro were launched, known as the Model A and the Model B. Both were based around a 2 MHz 6502 processor and featured the same operating system and language, BBC BASIC I (later BBC BASIC II), housed in 32 Kb of ROM. Both machines also had standard TV, cassette, RGB monitor, RS423 serial and analogue ports and three special Acorn-designed ports, the User Port, 1 MHz Bus and the Tube. The User Port was designed to allow peripherals such as turtles to be attached, the 1 MHz Bus for peripherals that needed direct system bus access and the Tube allowed the easy connection of a second processor. The main differences between the two systems were the amount of RAM (the Model A had 16 Kb and the Model B had 32 Kb) and the number of interfaces (the Model B was supplied with two additional interfaces, allowing a disc drive and a printer to be added). The BBC Micro could also be networked, with the addition of an optional Acorn Econet adapter.

There was also a variant released for the US and Canadian market. This was based on the BBC Model B, but included a speech synthesiser system and Econet interface as standard, and was fitted with BBC BASIC III (based on BBC BASIC II, but with a number of bug fixed and the addition of the COLOR keyword). However, problems gaining FCC approval delayed the introduction of the US variant, and it never gained the same degree of popularity that it did in the UK.

The original BBC Micro cost £235 or £335 (for the Model A and Model B, respectively), but this was later increased to £299 and £399. The Beeb turned out to be incredibly popular, and sold in excess of 1,000,000 units worldwide before it was discontinued in 1986. At one point it was the computer of choice in seven out of ten schools, and enjoyed a 60% market share. Acorn needed to produce something fairly spectactular to live up to the success of the BBC Micro.

Next: After the Beeb - the Electron and the Acorn Business Computer (1983 to 1985).

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Robert McMordie

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