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arbitrary quantities, and were each referenced through a Run Time Name, or RTN. Since an object could be referenced by several RTNs belonging to different spheres, they could easily be shared between programs, and were deleted only when the object's reference count of RTNs fell to zero. Linked lists were used very extensively within E4 to manage data structures, in fact the RTN list was about the only linear list there was. (The system generation process included a phase prosaically called "knitting" comprising a combination of macro expansion and procedural elements, by which the initial data structures were dynamically "knitted" together to create an input file for the assembler.)
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which prevented both processors operating simultaneously in special state, and a very minor modification to one of the processors' interface to store zero, allowing each processor to address a small dedicated memory area for processor-specific variables such as the current activity. However, the results were somewhat disappointing as E4 naturally spent a significant proportion of its time in special state even though efforts had always made to limit special state routines to 100uS at a time. Even running processor-bound user programs, the performance achieved was only of the order of 150% of that of a single processor, and no dual processor E4 systems were ever sold.
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roughly 50 cm wide and deep, 70 cm tall, and complete with power supply, typically weighed in excess of 25 kg. Modules were interconnected using a single type of interface, comprising two identical cards to be plugged into two modules to be connected, these cards themselves linked by a flat ribbon cable either one or two metres long. Thus, memory was just another peripheral (such as a printer) but was both input and output.
27:
309:) 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. Furthermore, the power system was set up as a peripheral with interrupt capabilities that gave the machine the ability to power down gracefully in an emergency.
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processed work from a queue, for example taking print jobs from a print queue and printing them. A special case was the Read Engine, which was the command processor. This was either associated with a terminal device (in which case it had a terminal device but no queue), or was a batch processor (in which case it had a queue but no device).
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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. This consisted of a "Nucleus" which looked after a collection of "Engines". An Engine was typically associated with a peripheral device and
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which created a price competitive small system for CTL. In 1984 all the subsidiaries were merged into the holding company
Information Technology Limited (ITL), replacing the CTL name. Nominally this was an efficiency measure, but it also positioned the company better for a possible public offering
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The ease with which multiple processor, store and peripheral modules could be built into a system, plus the need to extend the upper capability limits, prompted the development of a dual processor variant of E4. This was built entirely from standard modules except for a small synchronisation board
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Processors naturally had a number of interface slots bussed together, allowing connection to memory and peripheral modules as required. Memory modules had several, allowing them to be accessed by more than one processor as well as by disc controllers for DMA. Disc controllers could be connected to
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of the time. These three phases were mediated by voltage edges rather than pulses, as this was thought to be faster. Furthermore, the input and output impedances of ECL were comparable to the characteristic impedance of ribbon cable. This, together with the small voltage swings between the "0" and
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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. Standard modules were
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but having both base and limit). The processor had 3 segment registers referred to as X, Y and Z. The X segment was read/execute only and used to map code segments (corresponding to CS in the x86 architecture). It was not possible to execute code in the Y and Z segments, which were used for data
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in the use of (mainly) device-independent 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.
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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. Objects could be created in
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two processors as well as memory modules. All modules had a "1.x" type designation, for example, the original processor module was 1.11, memory modules were 1.2x, character peripherals were 1.3x, discs were 1.4x and magnetic tape devices were 1.5x. The standard interface was designated 1.01.
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The filing system, SDFS, was not part of the kernel but was a separate program. A multi-key indexed file system MKFS was also developed, and together with a transaction processing system and a report generator, formed the basis of many sales into commercial applications.
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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
493:. 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.
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In 1981 entrepreneur Tony Davies became
Managing Director. Under Davies CTL began buying in hardware, to be re-badged as CTL systems, recognising CTL could not afford to develop hardware at all levels. The first was a
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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.
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The operating system kernel was referred to as the Exec. Several simple ones (E1, E2 and E3) were developed in the early years of the company. E4, first in-house release around 1973, written entirely in
446:, increased market share. In 1980 two sibling companies Office Technology Limited (OTL) and Network Technology Limited (NTL), and a holding company Information Technology Limited (ITL) were created.
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Many universities were equipped with
Modular One systems, in part due to the government of the time having a 'buy British' policy. Acting as a front-end processor for the
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and
Sequoia Systems. However, sales of CTL's proprietary systems fell off before the new systems could be ramped up to replace them. The company was taken over by
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298:(roughly corresponding to DS and ES in x86). There were 8 addressing modes allowing access to data mapped by the segment registers in various ways.
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and 8-bit microprocessor communications controllers, retreating from the radical modular design, but it never gained a significant market share.
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but left to form CTL when he couldn't persuade
Elliott to incorporate his ideas in their next generation of computers. CTL was financed by the
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in 1989, primarily for its customers and extensive support network, which effectively ended CTL's era as a computer manufacturer.
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During the 1970s CTL operated modestly successfully in a number of niche markets, while larger
American competitors, such as
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mainframe, driving multiple online terminals or as a remote batch job entry station, was a major market for the
Modular One.
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Distinctive features of the processor were memory-mapped I/O and an early version of segmented memory (similar to the later
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principles, though lacking most of what are now considered essential features of the paradigm, such as inheritance.
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Very few Modular One computers now remain, possibly only the example being that restored by Redhawk Systems Ltd.
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semaphores to protect internal data structures from conflicts. It was based on an early version of
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Founder Iann Barron left in 1971, following the collapse of a major customer. He went on to form
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It never sold widely outside of the UK, and even in the UK it was surpassed in sales by
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Continuous Path: The Evolution of ProcesControl Technologies in Post-War Britain
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Modus and many of the applications were written in the high level language
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The various building blocks could be assembled and configured to produce a
547:(Thesis). University of Warwick. pp. 115–116, 120, 123, 127, 138–140
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Over the mid 1970s to mid 1980s the systems were cost reduced with TTL
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598:. 20th Annual AIAA/USU Conference on Small Satellites. p. 1.
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During the mid 1980s, the company decided that the future lay in
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In 1969, Computer Technology hired then up-and-coming architect
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279:"1" states made for low noise, reflection-free communication.
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The memory segmentation, together with two execution states (
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SpaceWire: Key principles brought out from 40 year history
257:(ECL) and was competitive with other first generation
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to design their new headquarters north of London, in
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51:. Unsourced material may be challenged and removed.
718:. Council of Industrial Design, The Design Centre.
253:The Modular One was a 16-bit computer built with
750:Defunct computer companies of the United Kingdom
648:Redhawk Systems Modular One conservation project
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610:"Computer Technology Ltd. and the Modular One"
627:"The History of Computer Science 1970 - 1979"
232:American Research and Development Corporation
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660:"Lucid language may help European computers"
465:and CTL attempted to make the transition to
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615:. Version 4. February 2023. pp. 14–16.
633:. University of Birmingham. Archived from
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411:were also available for the Modular One.
188:Tony Davies (Managing Director 1981-1989)
111:Learn how and when to remove this message
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745:Computer companies established in 1965
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49:adding citations to reliable sources
755:Defunct computer hardware companies
364:, was a multitasking kernel using
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427:. He was replaced as Chairman by
305:and non-interruptible privileged
740:Companies based in Hertfordshire
592:Paul Walker; Barry Cook (2006).
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666:. 30 November 1972. p. 513
36:needs additional citations for
735:1965 establishments in England
545:Department of Computer Science
288:fault-tolerant computer system
213:Information Technology Limited
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440:Digital Equipment Corporation
383:There was some similarity to
336:before the end of the 1970s.
330:Digital Equipment Corporation
245:, appeared for sale in 1968.
60:"Computer Technology Limited"
534:Hamilton, Ross (June 1997).
469:with re-badged systems from
241:The first CTL computer, the
16:British minicomputer company
205:Computer Technology Limited
124:Computer Technology Limited
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631:School of Computer Science
567:"Compact machine launched"
712:"Office beneath the skin"
686:"Survey of minicomputers"
433:London Weekend Television
452:Convergent Technologies
458:on the stock markets.
255:Emitter Coupled Logic
186:(Chairman 1971-1975),
276:magnetic-core memory
45:improve this article
637:on 7 February 2007.
341:bitslice technology
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228:Elliott Automation
442:(DEC) with their
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635:the original
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573:. 2 May 1968
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549:. Retrieved
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43:Please help
38:verification
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455:8086 system
249:Modular One
243:Modular One
224:Iann Barron
179:Iann Barron
151:Iann Barron
729:Categories
509:References
425:transputer
409:FORTRAN IV
332:(DEC) and
295:Intel 8086
174:Key people
71:newspapers
690:Computing
444:PDP range
362:assembler
497:See also
471:Motorola
401:Coral 66
366:Dijkstra
323:ICL 1900
265:Features
222:Founder
193:Products
129:Industry
696:8 April
670:8 April
577:9 April
551:6 April
431:, from
147:Founder
139:Founded
85:scholar
716:Design
347:Legacy
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613:(PDF)
541:(PDF)
421:Inmos
405:COBOL
92:JSTOR
78:books
698:2019
672:2019
579:2019
553:2019
467:Unix
407:and
385:Unix
234:and
142:1965
64:news
475:ACT
219:).
217:ITL
209:CTL
47:by
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