At that point in history, British Telecom was a state monopoly, and even by 1982 BT only allowed (via approval) the four British manufacturers (STC, GEC, Plessey, and Thorn-Ericsson) to supply its twenty five types of phone through them, and not independently.
When first acquired, the clubs membership was only open to employees and ex-employees of Plessey's and J. Samuel White & Co.
Plessey was also the lead contractor for the Ptarmigan communications system supplied to the British Army that adopted the Plessey System 250 architecture.
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After the sale of the Roborough site in Plymouth to Xfab, the original Plessey Semiconductors site at Cheney Manor, Swindon continued to operate under the Zarlink Semiconductor name until it was sold to MHS Industries in early 2008.
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By 1972 Plessey designed the first industrial Capability-based security computer, a fault-tolerant multiprocessor system called Plessey System 250.
The development of electronic systems however took longer than anticipated and the British equipment manufacturers, particularly Automatic Telephone & Electric (ATE), which later became part of the Plessey group feared that continuing to focus the bulk of their production on Strowger equipment would harm their export sales as Crossbar had already become popular throughout the world.
It was installed by Plessey and the first of many TXE2 type exchanges.
A variant of Coral 66 was developed during the late 1970s/early 1980s by the British GPO, in conjunction with GEC, STC and Plessey, for use on the System X digital telephone exchange control computers, known as PO-CORAL.
DPNSS was an active (and successful) collaboration between PBX manufacturers and BT which started relatively slowly (BT & Plessey) but quickly snowballed with MITEL, GEC, Ericsson, Philips and eventually Nortel all joining to create a powerful and feature rich protocol.
(The earlier Plessey 250 was one of the few other computers with capability architecture ever sold commercially).
In 1988 GEC announced a new partnership with the German electronics group Siemens to once again bid for Plessey.
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In 1971 Clark succeeded Field Marshal Lord Harding as chairman of Plessey.
A number of large scale manufacturing applications were developed in RPL, including that which was in use at Plessey/GPT limited in Liverpool and also the Trifid suite of manufacturing software.
In May 1996 the Marconi Type 91 'Martello' radar at Trimingham was sold to the Turkish Ministry of Defence and it was replaced by what used to be known as No 86 Signals Unit, with a Type 93 (Plessey type ADGE-305, NATO designation TGRI 50011) that had been moved from Hopton when that base was closed.
A number of large scale manufacturing applications were developed in RPL, including that which was in use at Plessey and GEC-Plessey Telecommunications limited in Liverpool and also the Trifid suite of manufacturing software.
MESAR 1 development commenced in 1982 as a partnership between Plessey, Roke Manor Research and the Defence Evaluation and Research Agency.