The BBC Master computer was released by Acorn Computers in 1986 as a successor to the BBC Micro, model B. The machine was built around the MOS technology 65SC12 processor. This is an enhanced CMOS version of teh nMOS-based 8-bit 6502. It uses less power than the 6502 and has an increased instruction set. Also, a few problems that existed in the 6502 were fixed with the 65C12. The BBC Master came in a few different models. One of the strengths of the architecture was that it could be expanded using a co-processor, that enabled it to run DOS Plus or the GEM graphical user interface.

The system was designed and built for the BBC as part of the push to enable computing in the British education system. The computer was backwards compatible with the BBC Micro, except for some games that used features on the BBC Micro that were not part of the standard.

The BBC Master was produced in a few variations. Not all were produced in large quantities, and some of them are hard to find.

• Master 128 - First model of the Master series
• Master Turbo - Featured a 65C102 co-processor @4MHz
• Master AIV - Master Turbo with a SCSI interface and a Videodisc
• Master ET - For use on a network, only had RGB and Econet connectors
• Master 512 - Intel 80186 co-processor @ 10MHz to run DOS Plus and GEM
• Master Scientific - Prototype, NS32016 co-processor @ 8MHz
• Master Compact - Compact version of the 128

• ECO-Net connector
• Audio Out
• Cassette port
• RS 432 communications port
• Analoge port
• RGB Monitor connector
• Composite Video connector
• RF Output for TV

The 6502 is an 8-bit MicroProcessor designed by MOS Technology. The team was led by Chuck Peddle and had also worked on the Motorola 6800. The 6502 is a simplified, but faster and cheaper design than the 6800.

The 6502 was introduced in 1975 and was the cheapest microprocessor on the market. Together with the Zilog Z80, the 6502 helped start the home computer revolution of the 1980s. The 6502 was used in a wide range of devices: the Atari 2600, the 8-bit Atari home computers, the Apple II, the Nintendo Entertainment System, the Commodore 64, the BBC Micro and many others. All used the 6502 or a variation of it.

The 6502 is a 1MHz design, while the 6502A is designed for 2MHz. The 6502A is 100% compatible with the original 6502.

Commodore soon bought MOS Technology, but conitnued to sell the microprocessor to competitors and licensed the design to other manufacturers.