ICL 2900 Series

The ICL 2900 Series was a range of mainframe computer systems announced by the UK manufacturer ICL on 9 October 1974. The company had started development, under the name "New Range" immediately on its formation in 1968. The range was not designed to be compatible with any previous machines produced by the company, nor with any competitor's machines: rather, it was conceived as a synthetic option combining the best ideas available from a variety of sources.

In marketing terms, the 2900 Series was superseded by Series 39 in the mid-1980s; however, Series 39 was essentially a new set of machines implementing the 2900 Series architecture, as were subsequent ICL machines branded "Trimetra".

When ICL was formed in 1968 as a result of the merger of International Computers and Tabulators (ICT) with English Electric Leo Marconi and Elliott Automation, the company considered a number of options for its future product line. These included enhancements to either ICT's 1900 Series or the English Electric System 4, and a development based on J. K. Iliffe's Basic Language Machine. The option finally selected was the so-called Synthetic Option: a new design starting with a clean sheet of paper.

As the name implies, the design was influenced from many sources. These included ICL's own earlier machines. The design of Burroughs mainframes was influential, although ICL rejected the concept of optimising the design for one high-level language. The Multics system provided other ideas, notably in the area of protection. However, the biggest single outside influence was probably the MU5 machine developed at Manchester University.

The 2900 Series architecture uses the concept of a "virtual machine" as the set of resources available to a program. The concept of a "virtual machine" in the 2900 Series architecture should not be confused with the way the term is used in other environments. Because each program runs in its own virtual machine, the concept may be likened to a process in other operating systems, while the 2900 Series process is more like a thread.

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