System X (telephony)

System X was the 2nd national digital telephone exchange system to be used in the United Kingdom. The first was a UXD5-Glenkindie Scotland 1979.

System X was developed by the UK Post Office (later to become British Telecom), GEC, Plessey, and Standard Telephones and Cables (STC) and first shown in public in 1979 at the Telecom 79 exhibition in Geneva Switzerland. In 1982, STC withdrew from System X and, in 1988, the telecommunications divisions of GEC & Plessey merged to form GPT, with Plessey subsequently being bought out by GEC & Siemens. In the late 1990s, GEC acquired Siemens' 40% stake in GPT and, in 1999, the parent company of GPT, GEC, renamed itself Marconi.

When Marconi was sold to Ericsson in January 2006, Telent plc retained System X and continues to support and develop it as part of its UK services business.

The first System X unit to enter public service was in September 1980 and was installed in Baynard House, London and was a tandem junction unit which switched telephone calls amongst around 40 local exchanges. The first local digital exchange started operation in 1981 in Woodbridge, Suffolk (near BT's Research HQ at Martlesham Heath). The last electromechanical trunk exchange (in Thurso, Scotland) was closed in July 1990—completing the UK's trunk network transition to purely digital operation and becoming the first national telephone system to achieve this. The last electromechanical local exchanges, Crawford, Crawfordjohn and Elvanfoot, all in Scotland, were changed over to digital on 23 June 1995 and the last electronic analogue exchanges, Selby, Yorkshire and Leigh on Sea, Essex were changed to digital on 11 March 1998.

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