Computer Technology Limited

Computer Technology Limited or CTL, was a British computer company google founded slightly later than Digital Equipment Corporation (DEC) in the United States.

Founder Iann Barron had worked for Elliot Computing but left to form CTL when he couldn't persuade Elliot to incorporate his ideas in their next generation of computers. He left CTL in 1971, going on to form Inmos and develop the transputer.

The first CTL computer (the Modular One) appeared for sale in 1969.

The Modular One

This was a 16-bit computer built with Emitter Coupled Logic (ECL) and was competitive with other first generation minicomputers. Its most distinctive hardware features were memory-mapped I/O, and an early version of segmented memory (similar to the later Intel 8086 but having both base and limit). The latter, together with two execution states (Normal State and Special State) made possible the implementation of a self-protecting operating system kernel (known as the Executive, or Exec). Such ideas were popular in British computer academia at the time and later were adopted by some US designs such as the aforementioned Intel 8086. Also, the power system was set up as a peripheral with interrupt capabilities which gave the machine the ability to power down gracefully in an emergency.

An important idea in Modular One was that the main memory was much like another peripheral, for instance a printer, but was both input and output. When an instruction (or data) was retrieved from memory, the request went out over a cable one or two metres long to another (memory) box, also about one metre cubed. It was thought that a voltage edge was faster than a pulse, so a request was represented by a single voltage transition. The word being read would travel the one or two metres, and then because reading magnetic-core memory destroys it's contents it would be sent to be re-written back to where it had been.

The Modular One was comparatively expensive. It was somewhat exotic in that its modular design resulted in almost every system delivered being somewhat different, which created a high maintenance burden. It never sold widely outside of the UK, and even in the UK it was surpassed in sales by DEC and Data General before the end of the 1970s. The systems were cost reduced with new technology over the mid '70s to mid '80s but never gained a significant market share.

Many universities were equipped with Modular One systems, in part due to the government of the time having a 'buy British' policy. ^[1]

Operating system

The Exec was known as E4. (E1, E2 and E3 were much simpler execs used only in the first few years of the company). E4 was based on an early version of object-oriented principles, though lacking most of what are now considered essential features of the paradigm. Objects included Activities (now more commonly known as tasks or processes), Segments (of memory), Files, Semaphores and Clocks. Another object type, the Sphere, was a run-time protection domain within which all other object types (including other Spheres) existed. There was some similarity to Unix in the use of serial byte oriented streams in the file system and interprocess communication, in contrast to the record-oriented file systems then dominant in commercial data processing. E4 also supported real-time priorities and virtual memory at the Segment level. It was a relatively elegant OS for its time but was never ported to other hardware, having been written entirely in assembler. (Appropriate and effective high-level language implementations were not readily available at the time.)

Later history

During the mid '80s, the company realised that the future lay in open systems and attempted to make the transition to Unix with re-badged systems from Motorola and Sequoia, however, sales of the proprietary systems fell off before the new systems could be ramped up to replace them, and the company was taken over by ACT in late 1989.^[2]

References

1. ^ Birmingham University School of Computer Science History - with photo,
2. ^ Scott, Anthony P.; Product Information Officer, Computer Technology Ltd., 1969-1971, edits of August 26, 2008