Editing System X (telephony) (section)

===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.