Mark Pack

BTW I am the only person ever to write software that was used in BOTH System X and System 12! There were strict rules preventing STC passing any software between the UK System X and ITT's System 12, but my software was not intended for System X so was legally used by a System 12 group. Meanwhile, GEC had a copy of it, and THEY used it for some System X work. As they were not part of ITT they were not restricted in using it - though I was never quite sure how they got a copy in the first place! (I think it was due to some other joint project which had a copy.)

Digital switches (telephone exchanges) were not called all system X! That was the name of the system specified by BT and designed and built by GEC/Plessey/STC. Competitors included Nortel's DMS-100 (Canada), AT&T's 4ESS (USA) and the ITT System 12 (Belgium/France? Germany). 4ESS was the world's first digital switch in 1976. Meanwhile optical fibre transmission was being invented at STL in Harlow (the R&D Labs of STC/ITT), leading to trials with BT and then STC becoming a major fibre manufacturer, and responsible for many of the international and intercontinental cables the internet still depends on. Sadly, NONE of the manufacturing companies mentioned above still exist in anything like their original form.

You could of course have added that Colossus was built by the Post Office research establishment (at Dollis Hill) using standard "PO Type 3000" relay sets and "Strowger pre-2000" equipment as any ex-PO/BT engineer who worked on them, like me, could tell you. :-)) As an aside the Research etablishment later moved to Martlesham where it became the world leader in fibre optics and what we now know as digital telephone exchanges (or "system X" as they were called initially); and the former head of BT is now Lib Dem peer Lord Valance.