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Useful Notes: BBC Micro
The BBC Microcomputer System (aka "BBC" or just "Beeb"), built by Acorn Computers under the auspices of (naturally) The BBC, was the most popular computer in British primary and secondary schools during the 1980s. The BBC had sought a microcomputer to serve as the cornerstone of their "Computer Literacy Project" and be used to demonstrate a wide variety of features on the educational TV series The Computer Programme; Acorn's microcomputer (known as the Proton in its prototype state) turned out to meet and exceed the BBC's ambitious specifications, but it also became known as a gaming platform and an early technology for computer special effects.

In November 1981, Acorn launched Model A and Model B of the BBC Micro, over a million of which would ultimately be sold. The difference between the two models was that the Model B had twice as much RAM, two more expansion ports and sold for 100 more. The Model A's scarcity of memory was a crippling enough drawback that most were upgraded at some point.

While the Beeb's basic specs were comparable to that of its main competitors, its peripheral interfaces were something else entirely. Like Acorn's previous home computer, the Atom, the Beeb was designed for expandability. True to its lofty goals, the fully-upgraded Model B featured:

  • TTL RGB and composite video output as well as the usual UHF TV modulator.
  • Standard serial and parallel ports (for printers or whatever took your fancy).
  • The best disk interface and filing system of any 8-bit home computer.
  • Logic inputs and outputs for controlling devices.
  • Analogue-to-digital converter inputs for measurements (and analogue joysticks, oh yes!).
  • A 1 MHz bus for fast data acquisition
  • A speech synthesiser
  • Econet (Acorn's proprietary networking system).
  • And last but not least, the Tube an advanced bus which could support and utilise a second processor.

A few of these upgrades were standard features of the rare North American version (whose display hardware was modified for output to NTSC televisions).

Second processors were actually available as well as the official Acorn model (shown off in the promo literature but rarely bought), there was the Torch Systems Z80 board (which could run their version of CP/M and business software), and a few other third-party systems. As it was, the Tube was really a developer feature, included to aid future prototyping the ARM processor was tested on it and the Acorn Archimedes developed with its aid.

Like the Apple ][ and Commodore 64, but unlike the ZX Spectrum and Amstrad CPC, the Beeb clocked its RAM at twice the speed of its CPU and therefore was able to switch alternately between CPU and video circuits without a speed penalty.

Like most 8-bit home computers, this one featured a BASIC interpreter (BBC BASIC) which was accessed directly from the command line. It also featured a native assembler for writing machine code.

Some of the platform's most impressive games—Elite, Exile, and The Sentinel—employed Procedural Generation to create vast universes in extremely limited memory. These titles continued to stand out when ported to far more powerful machines, and Elite launched an enduring subgenre of Wide Open Sandbox space-trading-and-combat sims.

In 1983, a stripped-down version of the Model B, the Acorn Electron (popularly nicknamed the "Elk"), was released to compete in the Spectrum's budget price range.

The Beeb remains a cult classic mainly because of its remarkable customisability. Network interfaces, extra tape and disk drives, and custom peripherals could be added easily. Several prominent early adopters, such as author Terry Pratchett, took this to its logical extreme and ended up with a machine at the centre of a dozen custom circuitboards that would turn the lights on, check the weather via a Teletext adaptor and display it on the screen, and play a fanfare as soon as he entered the room. After a while Pratchett forgot exactly what component did what and the machine seemed like some mysterious organic whole, inspiring the self-aware computer HEX from Discworld.

It also saw use in the entertainment industry, creating visual effects and synthesised music. One prominent use was by Queen in their song "A Kind of Magic". The BBC itself made as extensive use of this facility as it could, probably so they could be seen "eating their own dogfood", but also for practical reasons. While it depended on what you wanted, you could usually whip up programs for producing effects and captions in-house in a very short space of time. These could then be re-used on demand while productions had to jostle for time on one of the BBC's Quantel systems, they could have their own BBC Micro(s) as required.

The BBC Master (AKA Beeb Master or just Master), introduced in 1986, was the successor to the Model B, adding extra memory, upgrades to BBC BASIC, the operating system and the disk filing system, and a built-in word processor and spreadsheet. The BBC Master went through various models before finally being discontinued in 1994.

The Raspberry Pi is often portrayed as a Spiritual Successor, right down to having a Model A and Model B as a deliberate Shout-Out.


Specifications:

Processors
  • CPU: MOS 6502 (Model B+: MOS 6512A; BBC Master: Rockwell R65SC12), 2 Mhz.
  • GPU: Motorola 6845 + custom circuitry. The Electron replaced these with a custom ULA chip that also provided all I/O and sound.
  • Sound: Texas Instruments SN76489. The Electron replaced this with the aforementioned custom ULA, which reduced the number of sound channels from three to one.

Memory
  • Model A: 16K RAM; 32K ROM.
  • Model B, Electron: 32K RAM; 32K ROM.
  • Model B+ (1985): 64K or 128K RAM; 32K ROM.
  • BBC Master: 128K to 512K RAM, with separate video RAM; 64K ROM.

Display
  • 160*256, 320*256, or 640*256 graphical resolution. (Some of the higher-resolution graphics modes used 20K of RAM, and so were unusable on the Model A.)
  • 40*25 "teletext" mode (not available on the Electron).
  • Up to 8 colours. (There could be as many as 16 logical colours, but the second 8 were just flashing versions of the first 8.)

Sound
  • Four channels three square waves, one noise generator.


Games for the 8-bit Acorn family:

Original Titles

Ported, Cloned, or Concurrently Developed


3DO Interactive MultiplayerVideo Game SystemsAcorn Archimedes

alternative title(s): BBC Micro
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