Bbc Micro

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{{Infobox computer|Name = BBC Model A to Model B+128|Photo = |Type = 8-bit Microcomputer|Memory = 16 [Kilobyte (KiB) - 128 KB]s and associated peripherals designed and built by Acorn Computers Ltd for the BBC Computer Literacy Project operated by the British Broadcasting Corporation.

While twelve models were eventually produced in the range, the term BBC Micro is often colloquially used to refer to the first four (Model A, B, B+64 and B+128), with the later eight models referred to by the BBC Master and Acorn Archimedes names.

Background In the early 1980s, the BBC started what became known as the BBC Computer Literacy Project. The project was initiated partly in response to an extremely influential ITV documentary series The Mighty Micro, in which Christopher Evans (computer scientist) from the National Physical Laboratory, UK predicted the coming computer revolution and its impact on the economy, industry, and lifestyle of the United Kingdom.

The BBC wanted to base its project on a microcomputer capable of performing various tasks which they could then demonstrate in their 1981 TV series The Computer Programme. The list of topics included computer programming, computer graphics, sound and music, Teletext, controlling external hardware, artificial intelligence, etc. It decided to badge a micro, then drew up a fairly ambitious (for its time) specification and asked for takers.

The BBC discussed the issue with Clive Sinclair, who tried to offer the unsuccessful Grundy NewBrain micro to them, but it was rejected. The BBC made appointments to see several other British computer manufacturers, including Dragon Data, Ltd. and Acorn Computers Ltd.

The Acorn team had already been working on an upgrade to their existing Acorn Atom microcomputer. Known as the Proton, it included better graphics and a faster 2 MHz MOS Technology MOS Technology 6502 Central processing unit. The machine was only in prototype form at the time, but the Acorn team, largely made up of students including Sophie Wilson and Steve Furber, worked through the night to get a working Proton together to show the BBC. The Acorn Proton not only was the only machine to come up to the BBC's specification, but also exceeded it in nearly every parameter.

Market impact The machine was released as the BBC Microcomputer in late 1981 and became affectionately known as the Beeb. The machine was popular in the UK, especially in the educational market. As with Sinclair Research Ltd.'s ZX Spectrum, also released later in 1982, demand greatly exceeded supply. For some months, there were long delays before customers received the machines they had ordered. A brief attempt to market the machine in the United States failed, due largely to the predominance of the highly similar Apple II family. The success of the machine in the United Kingdom was largely due to its acceptance as an "educational" computer – the vast majority of UK schools used BBC Micros to teach computer literacy and information technology skills. Some British Commonwealth countries, like India, started their own Computer Literacy programs and used the BBC Micro.

Research Machines had, until this time, been one of the leaders in UK educational computer market. One of the main advantages which helped the BBC Micro in the educational market was its durable construction. The machine's casing and keyboard was solidly built compared to that of the ZX Spectrum, being able to cope with all the abuse that schoolchildren could throw at it.

The Model A and the Model B were initially priced at £235 and £335 respectively, but rising almost immediately to £299 and £399 due to increased costs.http://www.stairwaytohell.com/articles/cr-BBCMicro-CToday.html Acorn anticipated the total sales to be around 12,000 units, but eventually more than 1 million BBC Micros were sold.

The cost of the BBC Models was high compared to competitors such as the ZX Spectrum and Acorn attempted to counter this by producing a cut down version (although it did have the 32 kB random access memory of the Model B rather than the 16 kB of the Model A), intended more for game playing, the Acorn Electron in 1983; games written specially for the Electron's more limited hardware could usually also be run on the Model B.

Description Hardware features, Models A and B

The Model A had 16 KB of user RAM; the Model B had 32 KB of user RAM. A feature of the 6502-based hardware that the Micro shared with other 6502 computers such as the Apple and the early Commodore models was that the RAM was clocked twice as fast as the CPU (4 megahertz), with alternating access given to the CPU and the video display circuits. This gave the BBC Micro a fully unified memory address structure with no speed penalties. Most competing Z80-based micros with memory mapped display incurred CPU speed penalties depending on the actions of the video circuits (e.g. the Amstrad CPC and to a lesser extent the ZX Spectrum) or kept video memory completely separate from the CPU address pool (e.g. the MSX).

The machine included a number of extra Input/output interfaces: Serial port and Parallel port printer ports; an 8-bit general purpose digital I/O port; a port offering four Analog signal inputs, a light pen input, and switch inputs; and an expansion connector (the "1MHz bus") that enabled other hardware to be connected. Extra ROMs could be fitted (four in total without expansion hardware; sixteen with) and accessed via paged memory. An Econet network interface was available as an option; all logic boards had the space for the electronic components, but they were not normally fitted. Model B versions had a disc drive interface. Additionally, an Acorn proprietary interface called the "Tube (BBC Micro)" allowed a second processor to be added; several types of processor were offered by Acorn including 68000 versions. It was later used in third-party add-ons, including a Zilog Z80 board and Disk storage that allowed the BBC machine to run CP/M operating system programs.

The Tube interface allowed Acorn to use ARM_Limited CPU equipped BBC Micros as software development tools when creating the Acorn Archimedes. This resulted in the ARM development kit for the BBC Micro in 1986, priced at around £4000http://www.mcmordie.co.uk/acornhistory/archist.shtml. In 2006 a kit with an ARM7TDMI CPU running at 64 MHz, with 16MB of RAM was released for the BBC Micro and Master, using the Tube interface to turn the old 8 bit micros into 32 bit RISC PCs just as Acorn had done two decades previously.http://www.drobe.co.uk/riscos/artifact1557.html Possibly the best-known software to run on the Tube were an enhanced version of Elite (computer game) (see below) and a Computer Aided Design package which required a second 6502 CPU and a 5 dimensional joystick called a "Bitstick". The Model A and the Model B were built on the same Printed circuit board and a Model A could be upgraded to a Model B without too much difficulty. Users wishing to run Model B software needed only to add the extra RAM and the user/printer MOS Technology 6522 VIA (which many games used for timers etc) and snip a link, a task which could be achieved without soldering. To do a full upgrade with all the external ports did however require soldering the connectors to the motherboard.

Early BBC Micros used linear power supplies at the insistence of the BBC's engineering specification (which was originally designed so that Sinclair would get the contract), but these very hot running PSUs were soon replaced in production by switched mode units.

An apparent oversight in the manufacturing process resulted in a significant number of Model Bs producing a constant buzzing noise from the built-in speaker. This fault could be partly rectified by a soldering-capable person, by soldering a resistor across two pads.http://www.sprow.co.uk/bbc/doctor.htm#bzzzt

Hardware features: B+64 and B+128 Acorn introduced the Model B+ in mid 1985, increasing the total RAM to 64 KB and including floppy disk support as standard, but this had modest market impact. The extra RAM in the Model B+ BBC Micro was assigned as two blocks, a block of 20 KB dedicated solely for screen display (so-called "Shadow RAM (Acorn)" RAM) and a block of 12 KB of 'special' Sideways address space RAM. The much-needed memory increase provided by this new 1985 'Beeb' was a welcome development, but was seen as an eighteen months or so too late to challenge the increased specifications of new rival microcomputer systems. The B+128 came with an additional 64 KB ( 4 × 16 KB "Sideways" RAM banks) to give a total RAM of 128 KB.

The new B+ was incapable of running some original BBC B programs and games, such as, for example, the very popular Castle Quest. A particular problem was the replacement of the Intel 8271 floppy disk controller with the Western Digital 1770 — many game software programmers in particular had used copy protection techniques which involved direct access to the controller, and simply wouldn't run on the new system.

There was also a long-running problem late on in the B/B+'s life infamous amongst B+ owners, when Superior Software released Repton Infinity, which refused to run on the B+. A string of unsuccessful replacements were issued before one compatible with both was finally released.

Software and expandability .Large numbers of games were written for the Beeb, including the original version of the classic Elite (computer game). A range of hardware add-ons and expansions was available, and the machine had provisions for floppy disk drives and Econet networking hardware. There were also sockets for the addition of extra Read-only memory chips. The built-in ROM-resident BBC BASIC programming language interpreter (computer software) was by far the most sophisticated of its time, and wholly supported the machine's educational focus. Advanced programs could be written without having to wade into the jungle of assembly language programming (necessary with many competing computers). Should one want, or need, to do some assembly programming, BBC BASIC featured a built-in assembler.

When the BBC Micro was released competing PCs used Microsoft BASIC, or variants typically designed to resemble Microsoft BASIC. BBC Basic had the following advantages:

Support for named procedures, rather than relying upon GOTO/GOSUB;
Support for IF .. THEN .. ELSE
Support for high-resolution graphics (albeit with a clumsy syntax);
Support for four-channel sound (again, with a clumsy syntax);
In-line support for machine code, rather than requiring the use of a DATA statement and the use of POKE to get the machine code data set-up;
Long variable names (Microsoft BASIC at that stage supported long names, but with only the first two characters recognised, so that effectively it was limited to two-character names);
Support for pointer-based programming, like C, although using a different syntax.

Although appropriate content was little-supported by television broadcasters, telesoftware could be downloaded via the optional BBC Cheese Wedge and the other alternative teletext adaptors that emerged.

As the early BBC Micros had ample I/O allowing machines to be interconnected, and as many schools and universities employed the machines in Econet networks, numerous networked multiplayer games were created. With the exception of a roguelike game and a tank game (Bolo (computer game), for example), few rose to popularity; in no small measure due to the limited number of machines aggregated in one place. It has been suggested, but not verified, that the world's first networked multiplayer game was written for the BBC computer, a strategy wargame of some kind. A relatively late but well documented example can be found in a dissertation based on a ringed RS-423 interconnect.http://bishop.mc.duke.edu/bolo/guides/dissertation/

Successor machines and the retro scene In 1986, Acorn followed up with the BBC Master series, which offered memory sizes from 128 KB and many other refinements which improved on the 1981 original. It attracted more interest than the B+ upgrades, although at heart it was essentially the same 6502-based BBC architecture, with many of the upgrades that the original design had intentionally made possible (extra ROM software, extra paged RAM, second processors) now included on the circuit board.

However, Acorn had produced their own 32-bit RISC CPU in 1985 and were working on building a personal computer around it. This was released in 1987 as four models in the Acorn Archimedes series, with the lower-specified two models (with 512 KB and 1 MiB respectively) released as BBC Microcomputers.

The last model, the BBC A3000, was released in 1989 as essentially a 1 MiB Archimedes back in a single case form factor. The BBC closed the Computer Literacy Project two years later.

As of 2005, thanks to its ready expandability and I/O functions, there are still numbers of BBCs in use, and a retrocomputing community of dedicated users finding new things to do with the old hardware. A BBC B+ was observed running the communications link in an unattended water pumping station in Oxhey in 1995. They still survive in a few interactive displays in museums across the country, and Jodrell Bank apparently uses a BBC Micro to steer one of its satellite dishesThe Register: "My PC is older than yours", . There are also a number of BBC Micro emulators for many OSes, so that even the original hardware is no longer necessary.

Specifications (Model A to Model B+128) {| class="wikitable"! !! width="200" | Model A !! width="200" | Model B !! width="200" | Model B+64 !! width="200" | Model B+128|-| CPU| colspan="2" | MOS Technology MOS Technology 6502 at 2 megahertz| colspan="2" | MOS Technology MOS Technology 6502 at 2 MHz|-| Random-access memory| 16 KB| 32 KB| 64 KB composed of 32 KB standard memory, 20 KB video (Shadow RAM (Acorn)) memory and 12 KB extended (special Sideways) memory.| 128 KB composed of 32 KB standard memory, 20 KB video (Shadow) memory and 76 KB extended (Sideways) memory.|-| Read-only memory| colspan="2" | 32 KB ROM composed of 16 KB Acorn MOS (Machine Operating System), and 16 KB read-only paged space defaulting to the BBC BASIC programming language. Four paged 16KB ROM sockets standard, expandable to 16.| colspan="2" | 48 KB ROM composed of 16 KB MOS, 16 KB Disk Filing System, and 16 KB read-only paged space defaulting to the BBC BASIC.|-| computer keyboard| colspan="4" | Full-travel keyboard with a top row of ten red-orange function keys f_0-f_9.] digital RGB connector +5V/0V, 1v p-p composite colour or monochrome video (link S38) and built-in UHF (PAL) RF modulator.]| As Model B, but Modes 0, 1, 2, and 3 not available due to lack of memory.| colspan="3" | Configurable graphics in Modes 0-6 (see table below) based on the Motorola 6845 Video Display Controller or Mode 7, a special Teletext mode, based a Mullard Mullard SAA5050 Teletext chip and only taking 1 KB of RAM.|-| Sound| colspan="4" | Four independent sound channels (one noise and 3 melodic) using the Texas Instruments Texas Instruments SN76489 sound chip. Dedicated phoneme based speech synthesis hardware optional.]| colspan="4" | compact audio cassette interface (with a relay operated motor control), using a variation of the Kansas City standard data encoding scheme running at 1200 or 300 baud.]| colspan="2" | Optional floppy disk interface based on the Intel 8271 chip, also requiring the installation of the Disk Filing System (disk filing system) ROM (and of soldered connector on Model A). (5.25" floppy drive usually used).] controller based on the Western Digital WD1770 controller and Disk Filing System ROM as standard.|-| Hard disk| colspan="2" | None (lack of memory).| colspan="2" | Additional Advanced Disk Filing System ROM required, external drive unit connected to the 1 MHz Bus interface. (Winchester Hard disk drives in 5 MB, 10 MB or 20 MB sizes. Maximum of 512MB per drive, up to four drives).|-| Serial Interface| Optional upgrade, soldering required.| colspan="3" | 5-pin 'domino'-DIN connector RS-423 serial port.] Centronics-compatible parallel port.] programming language).|-| Analogue interface| Optional upgrade, soldering required.| colspan="3" | DB15 pin with four 8/12 bit analogue inputs based on uPD7002 IC (suitable for two joysticks), two inputs suitable for pushbuttons and an input for a light pen.]®| Optional upgrade, soldering required.| colspan="3" | 40-pin IDC connector for external second CPU. Options included a second MOS Technology 6502, a Zilog Z80, the BBC Cheese Wedge#ARM Evaluation System, or a National Semiconductor 32016 (the latter was either branded "BBC Microcomputer System - 32016 Second Processor" or "Acorn Computer - Cambridge Co-Processor"), other vendors added 6809, 6800, 68000 and 68008 with the addition of a co-processor adapter, it is possible to connect a 10MHz 80186 co-processor, that would normally reside inside a BBC Master, to a BBC Micro, thus enjoying a limited degree of PC compatibility.] (Optional extra)| colspan="4" | Econet large-scale low-cost networking system - around 100 kbit/s using the Motorola Motorola 6854 (standard on US model).|}

The case was designed by industrial designer Allen Boothroyd of Cambridge Product Design Ltd.

Display modes

Mode 7 was a Teletext mode and extremely economical on memory: it also made the computer useful as a Prestel terminal, which made it popular with travel agents, banks and stock traders for a while. Train time displays at UK stations were driven by BBC Master computers until around the late 1990s when they were gradually phased out.
Modes 0 to 6 could display a choice of colours from a logical palette of sixteen, though only eight colours were available; the eight basic RGB color model#24-bit representation colours (0-black, 1-red, 2-green, 3-yellow, 4-blue, 5-magenta, 6-cyan, 7-white) and eight colours in a flashing state, (8-black/white, 9-red/cyan, 10-green/magenta, 11-yellow/blue, 12-blue/yellow, 13-magenta/green, 14-cyan/red, 15-white/black)
Modes 3 and 6 were special software (framebuffer) text modes. To save RAM, the count of lines was reduced from 32 to 25. As this would reduce the height of the frame, filler rows were created between each line of text when the frame was output, where no pixels were read from the framebuffer. This creates characteristic black lines between the rows of text when a different background colour is set, and a blank gap at the bottom of the display with the left-over pixels. The screen mode is otherwise held in memory as a regular graphics mode.
In addition, the BBC B+ and the later Master allowed 'shadow modes', where the framebuffer was stored in 20 KB of extra RAM mapped to location 0x8000 onwards ('shadowing' the BASIC ROM mapped to that area), instead of taking up the user memory below 0x8000. This feature was enabled by setting bit 7 of the mode variable, i.e. by requesting modes 128–135.

Optional extras

Serial ROM cartridge filing system via a slot to the left of the keyboard - usually fitted as part of the Speech Upgrade
Speech synthesis hardware based around the Texas Instruments TMS5220 - standard on US model. The speech chips featured sampled phonemes spoken by BBC newscaster Kenneth Kendall. (Very few people bothered with this upgrade - the synthesiser's abilities were rather limited, and some games programmers succeeded in producing versatile software speech synthesis using only the standard sound hardware)

Use in the entertainment industry

The BBC Domesday Project, a pioneering multimedia experiment, was based on a modified version of the BBC Micro's successor the BBC Master.
Musician Vince Clarke of the British synth pop bands Depeche Mode, Yazoo (band), and Erasure used a BBC Micro (and later a BBC Master) with the UMI music sequencer to compose many hits . In music videos from the 1980s featuring Vince Clarke, a BBC Micro is often present or provides text and graphics such as the clip for Erasure's Oh L'Amour.
Queen (band) used the UMI Music Sequencer on their record A Kind of Magic . The UMI is also mentioned in the CD booklet. Other bands who have used the Beeb for making music are A-ha and the reggae band Steel Pulse.
The BBC Micro provided in-game graphics for the BBC TV show "The Adventure Game", where the BREAK key on the keyboard was covered by a plastic box to prevent accidental pressing.
Numerous 80s episodes of Doctor Who feature text, graphics, and sound effects generated by a BBC Micro computer. Such episodes include The Five Doctors (first broadcast in 1983) and The Twin Dilemma (first broadcast in 1984).