System X (telephony)

Type of telephone exchange in UK System X is the digital switching system installed in almost all telephone exchanges throughout the United Kingdom from 1980 until the 2020s. History Development System X was developed by Post Office Telecommunications (later to become British Telecom), GEC, Plessey, and Standard Telephones and Cables (STC), and was first shown in public in 1979 at the Telecom 79 exhibition in Geneva, Switzerland. STC withdrew from the project in 1982. In 1988, the telecommunications divisions of GEC and Plessey merged to form GPT, with Plessey subsequently being bought out by GEC and Siemens. In the late 1990s, GEC acquired Siemens' 40% stake in GPT. GEC renamed itself Marconi in 1999. 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. Implementation The first System X unit to enter public service, in September 1980, was installed in Baynard House, London and was a 'tandem junction unit' which switched telephone calls amongst some 40 local exchanges. The first local digital exchange started operation in 1981 in Woodbridge, Suffolk (near BT's Research HQ at Mart