[2] The Modular One was a 16-bit computer built with Emitter Coupled Logic (ECL) and was competitive with other first generation minicomputers.
A key feature, from which it derived its name, was that it was composed of separate processor, memory and peripheral modules sharing a common interface and physical form factor, so allowing them to be put together in any combination, housed one or two high in modular racking.
Every interaction over these interfaces comprised a 3-way handshake, which in the case of a processor accessing a memory module, consisted of send address, receive data, and send new data, a scheme well suited to the destructive read followed by rewrite required by magnetic-core memory of the time.
Processors naturally had a number of interface slots bussed together, allowing connection to memory and peripheral modules as required.
[3] Distinctive features of the processor were memory-mapped I/O and an early version of segmented memory (similar to the later Intel 8086 but having both base and limit).
Many universities were equipped with Modular One systems, in part due to the government of the time having a 'buy British' policy.
[5] Acting as a front-end processor for the ICL 1900 mainframe, driving multiple online terminals or as a remote batch job entry station, was a major market for the Modular One.
E4, first in-house release around 1973, written entirely in assembler, was a multitasking kernel using Dijkstra semaphores to protect internal data structures from conflicts.
It was based on an early version of object-oriented principles, though lacking most of what are now considered essential features of the paradigm, such as inheritance.
Objects included Activities (now more commonly known as tasks or processes), Segments (of memory), Files, Semaphores and Clocks.
E4 had a primitive command line interface but a multi-access operating system known as Modus was built on top of it for much greater flexibility and ease of use.
In 1984 all the subsidiaries were merged into the holding company Information Technology Limited (ITL), replacing the CTL name.
[citation needed] The company was taken over by ACT in 1989, primarily for its customers and extensive support network, which effectively ended CTL's era as a computer manufacturer.
[1] In 1969, Computer Technology hired then up-and-coming architect Norman Foster to design their new headquarters north of London, in Hemel Hempstead.
Foster responded to the company's need for an open office plan, as well as a compressed building schedule, by designing an innovative inflatable structure or "air tent" that was critically lauded by the architectural press at the time of its unveiling.