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Microsoft launched DOS on 12 August 1981 – the day IBM debuted its Personal Computer. Known as PC DOS on that machine (and marketed as MS-DOS on compatibles), its series of commands and programs soon became the standard for PCs, paving the way for Windows in November 1985.
But that first version of Windows was appalling. How did Microsoft achieve operating system dominance and how did it see off rivals as strong as CP/M, which had been around since the mid-1970s? As always in such battles for supremacy there were key moments – and a lot of luck – that worked in favour of the winner.