In January 1986 Acorn released the successor to its popular BBC Model B computer: the BBC Master. These microcomputers were backwards compatible with the Model B, allowing upgrading users to continue to use there existing software and hardware, but contained a number of enhancements.

The most popular model, the BBC Master 128, shipped with 128k of RAM (4 times as much as in a Model B), an enhanced operating system, the Advanced Disc Filing System, View and ViewSheet (Acorn's popular word processor and spreadsheet applications) built into its ROM and an updated version of BBC Basic.

Many of the Master 128s enhancements over the BBC Model B had there roots in third party expansions that were available for the Model B. For example on a Model B video memory was taken out of main RAM which could leave as little as 12k for applications and games but by adding Shadow RAM video memory would be taken from that instead leaving the full 32k for software to work with regardless of what video mode was in use. 32k of Shadow RAM was fitted as standard on the Master 128. Similarly Sideways RAM was memory you could fit into the Model Bs ROM expansion slots. This RAM was initially used by users to load ROM images from disc to prevent the need from having to swap ROMs in and out but over time a variety of novel uses were found for Sideways RAM including RAM discs and data storage for applications. Like Shadow RAM this was fitted as standard on the Master 128: it was supplied with four banks of 16k, for a total of 64k of Sideways RAM. To aid with the swapping of ROMs the Master included a expansion slots that essentially allowed ROMs to be plugged into the system without taking the lid off.

Expanding on the BBC Model B in this way provided the Master series with a very high degree of backwards compatibility. Unfortunately it also meant that the full 128k of RAM was difficult to access for most users and that applications like View and ViewSheet still found themselves limited to a working space of 32k.

Another enhancement over the Model B was the inclusion of an internal co-processor socket in addition to the Tube socket it retained from the Model B. In the same way as the Tube this allowed additional processors to be fitted to the Master to expand its power and abilities. There were a number of co-processors released to take advantage of this socket including a 65C102 based co-processor and a Intel 80186 based co-processor (more on the latter later!).

BBC Basic also contained minor upgrades to the version supplied with the Model B. The version supplied in ROM with the Master was able to be used with the systems Shadow RAM to give users access to 32k of program memory regardless of video mode but the system's remaining 64k of RAM would be unused (though it was possible with a bit of clever coding to page data and code in and out of Sideways RAM). However a version of BBC Basic was supplied on the Welcome disc called BAS128. This gave Basic programs access to 64k of RAM but, in my own experience, was significantly slower than the ROM based version - presumably because it was paging data in and out of Sideways RAM.