page_title: BBC Master
section_title: Specifications
hierarchical_section_title: BBC Master / Specifications
caption_attribution_description: English: Internal picture of BBC Master 128 showing additional romboard (Vine Micros RomBoard 4), installed ROMs and cooling fan. The fan has been retrofitted by the owner.
context_page_description: The BBC Master is a home computer released by Acorn Computers in early 1986. It was designed and built for the British Broadcasting Corporation and was the successor to the BBC Micro Model B. The Master 128 remained in production until 1993.
context_section_description: 2 MHz Rockwell R65SC12 processor
  128 KB ROM in the Master 128, Master Turbo, and Master 512. Comprising a 16 KB MOS (Machine Operating System), always accessible, and seven 16 KB sideways ROMs, any one of which could be paged into memory at a time:
  16 KB Terminal emulator and MOS extras (such as the cassette filing system) in paged ROM 15
  16 KB Acornsoft View (word processor) in paged ROM 14
  16 KB Advanced Disc Filing System in paged ROM 13
  16 KB BBC BASIC in paged ROM 12
  16 KB Acorn Screen Editor AKA Edit (text/BBC BASIC editor) in paged ROM 11
  16 KB ViewSheet (spreadsheet) in paged ROM 10
  16 KB Disc Filing System and Sideways RAM utilities in paged ROM 9
  64 KB ROM in the Master ET. Comprising a 16 KB MOS (Machine Operating System), always accessible, and three 16 KB sideways ROMs, any one of which could be paged into memory at a time:
  16 KB MOS extras (such as the cassette filing system and Sideways RAM utilities) in paged ROM 15
  16 KB Advanced Network Filing System in paged ROM 14
  16 KB BBC BASIC in paged ROM 13
  128 KB RAM, comprising:
  32 KB main user program/data storage
  20 KB "shadow" video memory (paged over main user RAM)
  12 KB OS workspace (paged over ROM)
  64 KB workspace accessible to user machine code applications (divided into up to four 16 KB regions to act like volatile paged ROMs)
  Full-travel keyboard with a top row of ten red-orange function keys ƒ0–ƒ9 and AT-style numeric keypad. The 'BREAK' reset key could be physically disabled by rotating a small plastic cam, particularly useful in educational environments
  Highly configurable graphics display based on the Motorola 6845. Unlike on the original BBC Micro, separate video RAM was used so that choosing a high-resolution mode did not reduce the amount of available user RAM. (However, user RAM could still be used as the video buffer if required, in order to allow effects such as double buffering.) Eight graphics modes were provided by the system ROM:
  Modes 0 to 6 could display a choice of colours from a logical palette of sixteen, though only eight physical colours could really be generated by the hardware: the eight RGB colours (black, red, green, yellow, blue, magenta, cyan, white) and the same colours in a flashing state;
  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.
  Mode 7's Teletext capability was provided by a Mullard SAA5050 Teletext chip.
  Four independent sound channels (one noise and three melodic) using the Texas Instruments SN76489 sound chip
  Built-in hardware support included:
  pluggable ROMs, directly or via cartridge slots
  floppy disc drives (both DFS and the newer ADFS supported) with WD1770 disc controller
  tape interface (with motor control), using a variation of the Kansas City standard data encoding scheme
  parallel printer port (Centronics compatible)
  serial communication (using RS-423, a superset of RS-232)
  display output for TV, RGB or 1v p-p video monitor
  a 15-pin 'D shaped' port with four analogue inputs (suitable for two joysticks, four digital/contact ports (for buttons) and a special Light pen input
  proprietary "Tube" interface for internal or external second CPU (in the Master 512 model, an 80186 was used; other options included a 3 MHz extra 6502, a Zilog Z80 for e.g. CP/M, an NS32016, an ARM1, and others)
  a 20-pin IDC style "user port" consisting of eight general purpose digital I/O pins (and two special handshaking ones) mapped directly into the 6522 VIA
  generic expansion through the "1 MHz bus", and
  Econet interface, installed by adding a module board and the ANFS ROM (fitted as standard to the Master ET machine)
  Several of the inputs were d
caption: Internal image of a Master 128 showing Vine Micro Romboard4 fitted, meaning the cartridge slots can no longer be used –  a non-standard cooling fan has also been added by the owner.
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