sideways and shadow RAM present on the B+. Releases 3 to 5 MOS 3 to MOS 5 shipped with the BBC Master Series systems, in the Master 128, Master ET, and Master Compact models respectively. The initial release of MOS 3 expanded upon the facilities provided in MOS 2 on the B+ to support additional hardware, provide a command line facility and extend the VDU driver code with enhanced graphics plotting abilities. Two notable versions were made public: version 3.20 being the most common, and version 3.50 (although this had more functionality and bug fixes it was not 100% compatible with some popular applications software so was offered as an optional upgrade only). MOS 4 was a stripped down version of MOS 3 intended for the similarly minimized Master ET, and a few minor bugs fixed. MOS 5 shipped with the Master Compact, and was much altered with some functions removed or highly amended. Credits With the exception of MOS 3.50 where the space was reclaimed for more code, the area normally hidden by the input/output memory locations (the 768 bytes from 0xFC00-0xFEFF inclusive) in the MOS ROM contained a list of names of contributors to the system. This could be recovered by extracting the ROM and reading its contents in an EPROM programmer. Those who did not have such a device could access the ROM on a Master by setting a test bit of an access control register, then using a machine-code program to copy the ROM directly to text-mode screen memory. The full text of the credit string in MOS 1.20 is as follows; no spaces occur after the commas to save memory: "(C) 1981 Acorn Computers Ltd.Thanks are due to the following contributors to the development of the BBC Computer (among others too numerous to mention):- David Allen,Bob Austin,Ram Banerjee,Paul Bond, Allen Boothroyd, Cambridge,Cleartone, John Coll,John Cox,Andy Cripps, Chris Curry, 6502 designers,Jeremy Dion,Tim Dobson,Joe Dunn,Paul Farrell, Ferranti, Steve Furber,Jon Gibbons,Andrew Gordon,Lawrence Hardwick,Dylan Harris, Hermann Hauser, Hitachi, Andy Hopper, ICL,Martin Jackson,Brian Jones,Chris Jordan,David King,David Kitson,Paul Kriwaczek, Computer Laboratory,Peter Miller, Arthur Norman,Glyn Phillips,Mike Prees,John Radcliffe,Wilberforce Road, Peter Robinson, Richard Russell,Kim Spence-Jones,Graham Tebby,Jon Thackray,Chris Turner,Adrian Warner, Roger Wilson,Alan Wright." Reception In interviews in 1993 and 2001, Acorn cofounder Hermann Hauser recounted that Microsoft's Bill Gates, having noticed that 1.5 million BBC Micros were sold, tried to sell MS-DOS to Acorn, but Hauser considered that adopting MS-DOS would have been a