BBC Master
The BBC Master is a home computer released by Acorn Computers in early 1986. It was designed and built for the British Broadcasting Corporation (BBC) and was the successor to the BBC Micro Model B. The Master 128 remained in production until 1993.

Design
The Master series featured several improvements on preceding BBC Micro models. The systems had 128 KB RAM as standard, alleviating the shortage of available RAM which had amongst other things discouraged use of the best graphics modes in the original design. The Master 128 and its variants had two cartridge slots mounted behind the new numerical keypad, these employing sockets that provided a superset of the Acorn Electron Plus 1 cartridge interface capabilities, supporting the use of physically compatible Electron cartridges, but also supporting enhanced electrical characteristics for some of the cartridge connector pins.

Rather than the MOS Technology 6502 microprocessor used by the Model B it ran on the slightly improved 65C12. The cost of this CPU compatibility with the Model B was that the address bus was still only 16 bits, meaning that only 64 KB could be directly addressed at any one time and the remaining memory had to be paged in as required.

This paging occurred via three separate pages, each with a codename, following previous BBC Microcomputer architecture traditions:

However the 65SC12's extra instructions allowed a little more to be shoehorned into the OS and BBC BASIC ROMs, limited by the memory architecture to 16 KB each. The improved version of BBC Basic was named Basic4.

Although the Master series was intended to be compatible with "legally written" software for the older models, there were some problems running older programs, particularly games. Conversely, although few programs were ever targeted specifically at Master series machines (except the Master 512), many later BBC games (and Master versions of earlier classics such as Elite) included enhanced features which took advantage of the extra memory.

An upgrade to the Master 128 operating system ROM was released by Acorn in early 1990, providing bug fixes and some performance and functionality enhancements, with the filing systems benefiting in particular. An input method was provided to permit the input of "foreign characters" or "top-bit-set characters" - character codes in the range from 128 to 255 - from the keyboard, and the View, Viewsheet and Edit applications all saw various levels of enhancement. One notable feature was the introduction of "relocatable" language (or application) ROM support, permitting appropriately written ROM-based software to automatically take advantage of a second processor, if fitted. Priced at around £45, it was noted that since the copyright message in the ROM was dated 1988 and the manual dated October 1989, such an upgrade might have been more widely adopted by users (and the relocatable ROM feature adopted by software producers) had it been released earlier, with the Master Compact ROM having already benefited from some of the featured improvements.

Models 

The Master series consisted of several different models, all of which apart from the Master Compact were variants of the same basic design.

Master 128 
This was the "foundation of the new BBC range" when launched. The 128 in the name referred to its 128 KB of RAM, though it also featured 128 KB ROM. A disc interface was fitted, but the drives themselves were not included in the base product, these being offered by third parties and by Acorn as an official expansion.

Master Turbo 
This was a Master 128 with 4 MHz 65C102 coprocessor card (which could be either bought with the machine or added to an existing Master 128).

Master AIV 
The Master AIV (Advanced Interactive Videodisc) was essentially a Master Turbo model with a SCSI interface and a VFS (Videodisc Filing System) ROM added, and formed the basis of the BBC Domesday System. Although normally supplied as part of a Domesday System, with LaserVision player, Domesday videodiscs, monitor and trackerball included, an upgrade kit was also available to turn a normal BBC Master into a Domesday System.

Master ET 
The ET (Econet Terminal) system was designed for use in a network and as such had no interfaces except RGB and Composite video, plus an Econet interface module and ANFS fitted as standard (it was usually an option). It used the same main circuit board as the Master 128, but the components for missing interfaces were simply not fitted (though there was nothing stopping them being added later by someone with appropriate soldering skills). The internal ROM also contained much less software than that of the Master 128.

Master 512 
This system boasted a coprocessor card with a 10 MHz Intel 80186 and 512 KB memory. It also had the ability to run DOS Plus and the GEM graphical user interface. The coprocessor card was introduced at £499 as an upgrade to the Master 128, but its price was subsequently reduced to £399.

The competitiveness of the Master 512 was constrained by its compatibility with various DOS applications, with this being limited by "protection and direct use of IBM hardware" by some applications. The additional memory requirements of DOS Plus, when compared to those of PC-DOS, and the requirements of the GEM desktop caused potential problems when running some applications, although memory expansions existed to mitigate such problems. System call compatibility was only assured for MS-DOS and PC-DOS 2.1, but other DOS versions were not supported, and undocumented system call usage ("fairly rare, but does include some Microsoft packages") could cause applications to run incorrectly. Software written for later GEM versions would also not necessarily run correctly.

A product by Shibumi Software called Problem Solver aimed to address various compatibility issues related to the increased speed of the coprocessor relative to a traditional IBM PC, display and keyboard differences (also supporting the BBC Model B keyboard for users of that machine with the co-processor attached), the behaviour of "memory resident packages" such as Sidekick, and the behaviour of particular applications. The product reportedly allowed well-known programs such as Ashton Tate's dBase III and Borland's Turbo C and Turbo Prolog to work on the coprocessor.

To remedy compatibility issues caused by a lack of memory, one company, Essential Software, provided an upgrade service augmenting the fitted RAM of the Master 512 upgrade with four 1 megabit devices providing 512 KB to yield a total of 1 MB of RAM. Priced at £99, and also compatible with Problem Solver, the upgrade overcame the elevated memory requirements of DOS Plus relative to MS-DOS and also allowed the system to meet the requirement of some applications to have 640 KB of memory available. Consequently, GEM 3, Ventura Publisher, WordPerfect 5.0 and dBase IV were all reported as being compatible. The company also produced a selection of utilities for the Master 512, including the Co-Processor Filing System (CPFS) which allowed the 512 KB of coprocessor memory to be used as a RAM disc by the computer when operating in its "native" BBC Micro mode.

Along with compatibility issues, the pricing of the Master 512 upgrade also inhibited its competitiveness. The estimated price of an IBM PC clone of £500-£800 compared "very favourably with the £900 needed for a complete Master 512", this being the Master 512 upgrade together with the base system, monitor and disk drives, considering that the clone would also include a monitor and drives in the price. The price was further reduced to £199 plus VAT in early 1987, with GEM Desk Top, GEM Write and GEM Paint being provided free with the upgrade, and a "final price cut to £99" was reported in 1989, effectively exhausting the remaining stocks. Although largely abandoned by Acorn as the company shifted its emphasis to the Archimedes range, one commentator considered it "one of the most exciting products Acorn has ever developed".

Master Scientific 
The Master Scientific was announced at the time of the BBC Master's launch, but was not produced. It was to have an 8 MHz 32016 coprocessor with 32081 floating point processor and 512 KB of RAM, running the PANOS operating system. This was similar to the previous external 32016 Second Processor. Ultimately, Acorn dropped the Scientific due to unspecified technical problems with the co-processor, also indicating that 512 KB of RAM appeared to be insufficient for the target audience, whose applications tended to need 1 MB of RAM, this already being provided by the upgraded 32016 Second Processor product known as the Cambridge Co-Processor.

Master Compact 

This model is, as the name indicates, a compact version of the Master 128 (ostensibly known as the "Baby B" during development) with some expansion functionality removed and other expansion options added, and with different bundled software. Unlike previously released Acorn microcomputers, it was sold by Acorn as a complete system bundled with disk drive and monitor (and the first high-volume system from Acorn to do so, preceded by the unreleased Acorn Business Computer and low-volume Acorn Cambridge Workstation), aiming to provide a "one plug" solution that had, at the time of release, been successfully popularised by manufacturers such as Amstrad. Indeed, one reviewer gave credit to Amstrad for having engineered the delivery of "an innovative, cheap machine for education" – the Compact – through robust competition with Acorn in the sector.

Although the Compact has a "three box" arrangement, the main functionality of the system is actually provided in the keyboard unit, much like the Master 128, but rather reduced in size in comparison to the Master 128 and Model B, being styled on the Acorn Communicator. The unit under the monitor housed a -inch floppy disk drive and the system power supply. Both monitors supplied with the Compact were Philips models: a "green screen" monochrome monitor for high-resolution applications connected using "an Electron-style phono socket", whereas the colour monitor provided a 0.42mm dot pitch "generally billed as high resolution" and offered the traditional RGB monitor connector used by previous Acorn machines. However, the colour monitor also provided a SCART connector, anticipating "future applications" employing more colours and even "overlaying video pictures".

The cartridge and cassette ports were removed as a space saving measure, and RS-232 hardware not populated on the circuit board as standard. A multifunction mouse and joystick port was provided as a 9-pin D type with its function configured in software. A Centronics printer interface was also provided. The 1 MHz bus and analogue port were not provided on the Compact. Additionally, no internal sockets were provided for adding a co-processor or 2nd processor. However, the machine did include a 50-way expansion edge connector on the right side of the keyboard, that was similar to cartridge socket #3 on a Master 128. Various third-party suppliers restored some of the removed functionality via this connector such as support for Electron and Master 128 cartridges and the provision of various BBC Micro expansion connectors.

Unlike the other models in the series which provided a battery-backed clock and memory for configuration settings, the Compact utilised EEPROM storage for its configuration with support for only a limited number of writes, making the EEPROMs "a consumable, like a battery" requiring "replacement at intervals". Hence, it had no built-in real-time clock facility, although the time could be fetched via Econet where available, being applied to ADFS file timestamps. As a result of this, the *TIME and TIME$ commands returned dummy values. Only the ADFS Version 2 filing system was supplied as standard, running via a Western Digital 1772 chip (a faster version of the widely used 1770), though it is possible to load a 1770 DFS ROM into sideways RAM, or to insert a ROM or EPROM containing it.

The User Port signals, although not available directly via a dedicated User Port connector such as provided on the other BBC models, could be accessed via the following method:

The (9-pin joystick) port is derived from port B of the user VIA, without extra buffering, and may thus also be used for output as well as input. For applications requiring the use of the 'USER PORT' as used in other BBC computers, the three signals that are not provided on the joystick port (PB5, PB6 and PB7) are available on the expansion port.

The keyboard on the Compact was the first to move away from using the traditional "sprung-key" keyswitch design used by the rest of the BBC Micro family. Instead, it used a rubber-plastic moulding membrane.

The chip-count was also reduced vs. the rest of the Master range, via the use of 4x custom gate array chips.

The version of BASIC on the Compact included re-coded mathematical routines, said to provide a 30% speed increase over the version included in the rest of the Master series. This version of BASIC was called Basic4(1986), aka 'BASIC41'. This was later replaced with version 'BASIC42' in 1987. This later BASIC ROM included the updated message (vs previous BBC BASIC ROMs):

 Roger Wilson & R.A. Sack

Software for the Compact was comparatively expensive (typically £20 for a game) due to the much lower demand for the -inch disk format (-inch was the standard for the Master and earlier BBC Micro).

The Compact included Acorn's first publicly available GUI. Little commercial software, beyond that included on the Welcome disk, was ever made available for the system, despite the claim by Acorn at the time that over 100 titles would be "set for distribution on 3.5in disc format for the Compact launch". The most avid supporter of the Master Compact appeared to be Superior Software, who produced and specifically labelled their games as 'Master Compact' compatible.

The machines were built by Rank Xerox in Hertfordshire. Ultimately, the Compact was discontinued in 1989 with "over eighty thousand Compacts and Olivetti's Prodest version" having been sold, with Acorn shifting its focus to the Master 128 as "its core 8-bit machine".

Olivetti Prodest PC128S 

Olivetti were named as being interested in releasing a version of the Master Compact in Italy under the Olivetti Prodest brand, subsequently announcing the model as the PC128S aimed at the home and small business markets.

Specifications

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 directly wired to specific registers in order to allow the hardware to do some of the heavy lifting. For example, the light-pen input would directly halt a counter which was started by the start of the vertical sweep of each display refresh, making calculation of where the lightpen was touching the screen little more than a simple divide/remainder operation. Likewise, the motor control relay for the audio cassette tape was controlled by a simple command and could be readily used in numerous control applications.

See also
RISC OS character set for the code page layout of the BBC Master

References

External links
 http://bbc.nvg.org/doc/

Acorn Computers
6502-based home computers
Home computers
Master