Editing System X (telephony) (section)

==History==

===Development===
System X was developed by [[Post Office Telecommunications]] (later to become [[British Telecom]]), [[General Electric Company|GEC]], [[Plessey]], and [[Standard Telephones and Cables]] (STC), and was first shown in public in 1979 at the Telecom 79 exhibition in Geneva, Switzerland.<ref>{{Cite web|title=Exhibits: System X|url=https://www.communicationsmuseum.org.uk/systemx/|access-date=2021-05-27|website=The Communications Museum Trust}}</ref> STC withdrew from the project in 1982. In 1988, the telecommunications divisions of GEC and Plessey merged to form [[GEC Plessey Telecommunications|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 Electronic Systems|Marconi]] in 1999.

When Marconi was sold to [[Ericsson]] in January 2006, [[Telent|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|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 [[Adastral Park|BT's Research HQ]] at [[Martlesham Heath]]). BT's 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, South Lanarkshire|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.

In addition to the UK, System X was installed in the [[Channel Islands]], and several systems were installed in other countries, although it never achieved significant export sales.

=== Small exchanges: UXD5 ===
Separately from System X, BT developed the UXD5 ("unit exchange digital"), a small digital exchange which was cost-effective for small and remote communities. Developed by BT at Martlesham Heath and based on the Monarch [[PABX]], the first example was put into service at [[Glenkindie]], Scotland, in 1979, the year before the first System X.<ref>{{Cite web|last=Ames|first=John|date=2015-12-09|title=Memories of the Glenkindie telephone exchange|url=https://blog.nms.ac.uk/2015/12/09/memories-of-the-glenkindie-telephone-exchange/|access-date=2021-05-27|website=National Museums Scotland}}</ref> Several hundred of these exchanges were manufactured by [[Plessey]]<ref>{{Cite web|title=History of Plessey|url=https://www.britishtelephones.com/histples.htm|access-date=2021-05-27|website=www.britishtelephones.com}}</ref> and installed in rural areas, largely in Scotland and Wales. The UXD5 was included as part of the portfolio when System X was marketed to other countries.