The British Broadcasting Corporation Microcomputer System, or BBC Micro, is a series of microcomputers and associated peripherals designed and built by Acorn Computers in the 1980s for the BBC Computer Literacy Project. Designed with an emphasis on education, it was notable for its ruggedness, expandability, and the quality of its operating system. An accompanying 1982 television series, The Computer Programme, featuring Chris Serle learning to use the machine, was broadcast on BBC2.
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During the early 1980s, the BBC started what became known as the BBC Computer Literacy Project. The project was initiated partly in response to an ITV documentary series The Mighty Micro, in which Christopher Evans of the UK's National Physical Laboratory predicted the coming microcomputer revolution and its effect on the economy, industry, and lifestyle of the United Kingdom.[1]
The BBC wanted to base its project on a microcomputer capable of performing various tasks which they could then demonstrate in the TV series The Computer Programme. The list of topics included programming, graphics, sound and music, teletext, controlling external hardware, and artificial intelligence. It developed an ambitious specification for a BBC computer, and discussed the project with several companies including Acorn Computers, Sinclair Research, Newbury Laboratories, Tangerine Computer Systems, and Dragon Data.[1]
The introduction of a specific microcomputer to a more general computer literacy initiative was a topic of controversy, however, with criticism aimed at the BBC for promoting a specific commercial product and for going beyond the "traditional BBC pattern" of promoting existing information networks of training and education providers. Accusations were even levelled at the Department of Industry for making the BBC "an arm of Government industrial policy" and using the Computer Literacy Project as a way of "funding industry through the back door", obscuring public financial support on behalf of a government that was ostensibly opposed to subsidising industry.[2]
The Acorn team had already been working on a successor to their existing Atom microcomputer. Known as the Proton, it included better graphics and a faster 2 MHz MOS Technology 6502 central processing unit. The machine was only at the design stage at the time, and the Acorn team, including Steve Furber and Sophie Wilson, had one week to build a working prototype from the sketched designs.[3] The team worked through the night to get a working Proton together to show the BBC.[4] Although BBC expected a computer with the Zilog Z80 CPU and CP/M operating system, not the Proton's 6502 CPU and proprietary operating system,[5] the Proton was the only machine to match the BBC's specification; it also exceeded the specification in nearly every parameter.[1] Based on the Proton prototype the BBC signed a contract with Acorn as early as February 1981; by June the BBC Micro's specifications and pricing were decided.[6] As a concession to the BBC's expectation of "industry standard" compatibility with CP/M, apparently under the direction of John Coll, the Tube interface was incorporated into the design, enabling a Z80 second processor to be added.[7] A new contract between Acorn and BBC Enterprises was agreed in 1984 for another four-year term, with other manufacturers having tendered for the deal. An Acorn representative admitted that the BBC Model B would not be competitive throughout the term of the renewed contract and that a successor would emerge.[8]
The machine was released as the BBC Microcomputer on 1 December 1981, although production problems pushed delivery of the majority of the initial run into 1982.[6][10][better source needed] Nicknamed "the Beeb",[11] it was popular in the UK, especially in the educational market; about 80% of British schools had a BBC microcomputer.[12][13]
BYTE called the BBC Micro Model B "a no-compromise computer that has many uses beyond self-instruction in computer technology". It called the Tube interface "the most innovative feature" of the computer, and concluded that "although some other British microcomputers offer more features for a given price, none of them surpass the BBC ... in terms of versatility and expansion capability".[14] As with Sinclair Research's ZX Spectrum and Commodore International's Commodore 64, both released the following year, in 1982, demand greatly exceeded supply. For some months, there were long delays before customers received the machines they had ordered.
A key feature of the BBC Micro's design is the high-performance RAM it is equipped with. A common design note in 6502 computers of the era was to run the RAM at twice the clock rate as the CPU. This allows a separate video display controller to access memory while the CPU is busy processing the data just read. In this way, the CPU and graphics driver can share access to RAM through careful timing. This technique is used, for example, on the Apple and the early Commodore models.[6][43][38]
The BBC machine, however, was designed to run at the faster CPU speed, 2 MHz, double that of these earlier machines. In this case, bus contention is normally an issue, as there is not enough time for the CPU to access the memory during the period when the video hardware is idle. Some machines of the era accept the inherent performance hit, as is the case for the Amstrad CPC, Atari 8-bit family, and to a lesser extent the ZX Spectrum. Others, like the MSX systems, use entirely separate pools of memory for the CPU and video, slowing access between the two.
Furber believed that the Acorn design should have a flat memory model and allow the CPU and video system to access the bus without interfering with each other.[5] To do so, the RAM has to allow four million access cycles per second. Hitachi was the only company considering a DRAM that runs at that speed, the HM4816. To equip the prototype machine, the only four 4816s in the country were hand-carried by the Hitachi representative to Acorn.[44]
The National Semiconductor 81LS95 multiplexer is needed for the high memory speed. Furber recalled that competitors came to Acorn offering to replace the component with their own, but "none of them worked. And we never knew why. Which of course means we didn't know why the National Semiconductor one did work correctly. And a million and a half BBC Micros later it was still working and I still didn't know why". Another mystery was the 6502's data bus. The prototype BBC Micro exceeded the CPU's specifications, causing it to fail. The designers found that putting a finger on a certain place on the motherboard caused the prototype to work. Acorn put a resistor pack across the data bus, which Furber described as "'the engineer's finger' and again, we have no idea why it's necessary, and a million and a half machines later it's still working, so nobody asked any questions".[5]
The Tube interface allowed Acorn to use BBC Micros with ARM CPUs as software development machines when creating the Acorn Archimedes. This resulted in the ARM development kit for the BBC Micro in 1986, priced at around 4000.[46] From 2006, a kit with an ARM7TDMI CPU running at 64 MHz, with as much as 64 MB of RAM, was released for the BBC Micro and Master, using the Tube interface to upgrade the 8-bit micros into 32-bit RISC machines.[47] Among the software that operated on the Tube are an enhanced version of the Elite video game and a computer-aided design system that requires a second 6502 CPU and a 3-dimensional joystick named a "Bitstik"[1].
During 1986, Acorn followed up with the BBC Master, which offers memory sizes from 128 KB and many other refinements which improves on the 1981 original. It has essentially the same 6502-based BBC architecture, with many of the upgrades that the original design intentionally makes possible (extra ROM software, extra paged RAM, second processors) now included on the circuit board as internal plug-in modules.
Not all ROMs offer star commands (ROMs containing data files, for instance), but any ROM can "hook" into vectors to enhance the system's functionality. Often the ROM is a device driver for mass storage combined with a filing system, starting with Acorn's 1982 Disc Filing System whose API became the de facto standard for floppy-disc access. The Acorn Graphics Extension ROM (GXR) expands the VDU routines to draw geometric shapes, flood fills, and sprites. During 1985 Micro Power designed and marketed a Basic Extension ROM,[67] introducing statements such as WHILE, ENDWHILE, CASE, WHEN, OTHERWISE, and ENDCASE, as well as direct mode commands including VERIFY.
When the BBC Micro was released, many competing home computers used Microsoft BASIC, or variants typically designed to resemble it. Compared to Microsoft BASIC, BBC BASIC features IF...THEN...ELSE, REPEAT...UNTIL, and named procedures and functions, but retains GOTO and GOSUB for compatibility. It also supports high-resolution graphics, four-channel sound, pointer-based memory access (borrowed from BCPL), and rudimentary macro assembly. Long variable names are accepted and distinguished completely, not just by the first two characters.
The Plus 3 included an uprated square black power supply unit with mains cord, manufactured by STC, designed and manufactured in England to BS 415 and BS 5850, that was designed to power the Plus 3, in addition to the Electron and the Plus 1 interface as well.[105] This replaced the original cream-coloured "wall wart" style power supply, designed to BS 415 and manufactured in Hong Kong.
The direct origins of the Slogger product appear to be a board designed by Andyk Limited,[128] announced as the Fast Electron Board in late 1985 with a price of 29.99,[90] whereas the Elektuur modification was described in an article in Dutch Electronics magazine Elektuur and intended for users to perform at home.[129]
A conceptually similar predecessor to the software-based simulator was published by Electron User in early 1987, offering a monochrome Mode 4 simulation of the Teletext display, using the lower 25 character lines of the screen to show the Teletext output, reserving several lines at the top of the screen for a representation of Mode 7 used to prepare the eventual visual output. However, the program did not support direct access to Mode 7 memory locations. The author noted that a Mode 2 version would have been possible but would have required a redesigned character set and "too much memory".[140] 2ff7e9595c
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