Time Sharing Limited

Time Sharing Limited (TSL) was founded in 1967^[1] by Richard ("Dick") Evans who had been impressed by Digital Equipment Corporation's minicomputers. It started service from a small office on Great Portland Street, London, with a dual, fault-tolerant system consisting of a front-end switch directing traffic to two units, each consisting of a PDP-7 and a PDP-8. The PDP-7 interpreted messages and the PDP-8 ran the appropriate application. A PDP-9 controlled access to persistent storage based on NCR CRAM Memory. The system used the TELCOMP interpretive language that had been developed by Bolt, Beranek and Newman.

Customers leased a modem from the General Post Office (later British Telecom) and a Westrex Teletype Model 33 from TSL. Line speeds were limited to 110 Baud (about 10 characters per second [CPS]). Customers were charged for each minute that they were logged onto the system.^[2] The initial persistent storage system was based on NCR CRAM units, which used magnetic cards hanging from a digitally addressed set of rods.

TSL quickly developed a range of applications for business, scientific and engineering customers. The most highly used were the PERT^[3] application, for critical path network planning, and an embryonic corporate modeling tool that could be regarded as a forerunner to spreadsheets. TSL soon licensed programs from other DEC customers, including the Nastran finite element modeling system and an early Database Management System called Oliver. TSL's Consultancy Division also developed applications, or modified services, for its customers. The most advanced applications used the MACRO-10 assembly language.