ICL 2900 Series

The ICL 2900 Series is a range of mainframe computers built by the British manufacturer International Computers Limited, formed in 1968 through a merger of several British computing companies, and unveiled on October 9, 1974. Rather than extend any of ICL's existing machines, the 2900 was designed from scratch under what ICL called the Synthetic Option, drawing on ideas from Burroughs mainframes, the Multics operating system and the Manchester University MU5 machine, and it was not built for compatibility with earlier ICL systems or competitors' equipment. Each program ran in its own protected virtual machine environment, with sixteen hardware protection levels and a hardware supported call stack, an advanced design for its time; ICL marketed the same underlying architecture through the mid-1980s as the Series 39 and later as Trimetra.