of the Master series features an integrated display, which had been criticised in some reviews of the ABC series. Around two years after the unveiling of the ABC range, the Master Compact eventually introduced the practice of bundling a display and storage into Acorn's traditional product range. Whereas the different models in the ABC range were combinations of a "host" computer based on the BBC Micro and a second processor fitted inside the display unit, the equivalent Master-series variants were generally accommodated by plug-in coprocessor cards fitted inside a Master 128 or Master Econet Terminal (ET), these models being the foundation of the range. It was therefore possible to acquire and upgrade the Master 128 or ET to one of the other models by installing the appropriate coprocessor card, and unlike the ABC whose models could be purchased as complete systems, only the Master 128 and ET were offered by Acorn as systems with the coprocessors offered separately as "modules" to realise the desired variants. A more direct legacy of the range concerns the BBC Model B+ whose motherboard has its origin as the BBC Micro "host" found in the different ABC models: a design using 64-kilobit RAM chips, an updated disk controller, and support for shadow RAM. Given perceptions of one ABC model as the BBC Model C, the Model B+ could be regarded as delivering the basis of that widely expected model. Having successfully pursued a similar strategy to that of the Acorn Business Computer, Torch were said to be "actively evaluating the B+ motherboard", having used the previous BBC Micro motherboard as the basis of the company's earlier products. Torch's own Graduate product had been noted as potentially filling a gap within the ABC range, this being the "big jump" from the Z80-based ABC 100 systems to the 80286-based ABC 300 models. The 1982 vision of microcomputers acting as terminals to a "Universal Gluon" expansion did eventually come to pass through the availability of a number of third-party expansions for the BBC Micro such as the Cambridge Microprocessor Systems 68000 second processor, Flight Electronics 68000 processor board, and the Micro Developments MD512k Universal Second Processor System. Meanwhile, various companies pursued the development of Tube-based second processor solutions involving the 68000, neglected by Acorn in its own offerings, such as the CA Special Products Casper board and the HDP68K board featured in the Torch Computers Unicorn, the latter