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The BBC Master was 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 featured several improvements on its predecessor. The systems had 128Kb RAM as standard, alleviating the shortage of available RAM which ''inter alia'' discouraged use of the best graphics modes in the original design, and had two cartridge slots mounted above the numerical keypad. Rather than the 6502 Microprocessor used by the Model B it ran on the slightly improved 65C102 : the cost of this CPU compatibility with the Model B was that the address bus was still only 16 bits, meaning that only 64Kb could be directly addressed at any one time and the remaining memory had to be paged in as required. However the 65C102's extra instructions allowed a little more to be shoehorned into the OS and BBC BASIC ROMs, limited by the memory architecture to 16Kb each. Although the Master 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. MODELS The Master was available in several different models. Master 128 This was the standard issue computer. The 128 in the name referred to its 128Kb of RAM, though it also featured 128Kb ROM. Master Turbo This was a Master with 4MHz 65C02 second processor card (which could be either bought with the machine or added to an existing Master 128). Master ET The ET (Econet Terminal) system was designed for use in a network and as such had no tape or disk interfaces but had the Econet interface fitted as standard (it was usually an option requiring the addition of extra chips). It was based on a Master 128 main board and the components for missing interfaces were simply not fitted (though there was nothing stopping them being added later by someone with appropriate soldering skills). Master 512 This system boasted a second processor card with an 8MHz Intel 80186 and 512Kb memory. It also had the ability to run DOS+ and the GEM graphical user interface. Master Compact in a separate unit underneath the Display .]] This model separated the keyboard from another unit which could be placed under the monitor. Only the ADFS file system could be used, preventing backward compatibility with DFS disks (though it was possible to load a 1770 DFS ROM into sideways RAM, or to insert a ROM or EPROM containing it). The Master Compact also utilised a limited re-burn EEPROM, instead of the battery backed CMOS memory found in the other models. The unit under the monitor housed a 3.5 inch Floppy Disk drive and the system power supply. The remainder of the system was housed in the same unit as the keyboard, much like a conventional Master 128. The cartridge and cassette ports were removed as a space saving measure. The loss of the latter was a move Acorn later came to regret. Software for the Compact became very expensive (typically £20 for a game) due to the small user base. The Compact included a copy of Acorn's first public GUI interface. No commercial software or utilities, others than those included on the Welcome disk were ever made available for the system. NOTABLE APPLICATIONS The BBC Master Turbo was the basic hardware platform required to run the 1986 BBC Domesday Project . Also required were a SCSI interface and Videodisc player, both of which were designed specifically for this application. SPECIFICATIONS
Several of the inputs where specialy wired up to specific registers as to allow the hardware to do some of the heavy lifting. For example the ' {Link without Title} ' input would directly halt a counter which was started by the start of the vertical sweep of each display refresh; hence making the calculation of where the lightpen was touching the screen little more than a simple divide/remainder operation. Likewise the motor control of the audio cassette tape was easily controled by a command; and as it powered a relay; could be readily used for all sorts of experiments. |
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