1.4 - Hardware technology in the ICT/ICL 1900 Range.

(Based on the talk given by Brian Procter at the London 1900 Seminar May 1996. Edited by Keith Crook and Virgilio Pasquali -  November 2003)

 

This section outlines the technology changes which took place during the lifetime of the 1900 and traces some of their impacts on machine specifications and design. Like most successful product ranges the 1900s exhibited a mixture of innovative leaps forward followed by periods of consolidation and evolution. Initially in contrast to today's position ICT had to do almost everything itself. ICT engineers selected circuit families, designed the Printed Circuit Board (PCB) technology for mounting and connecting the logic circuits then the next level of connection between the boards and finally the cabling, power, cooling and cabinets to make up the complete processor product.

 

Design tools were needed to aid the designers and to present information to manufacturing. Over the period of the 1900 series there was a great increase in the complexity of the design process made possible by a continuing investment in design tools. Manufacturing faced various challenges. Technologies demanded increasingly complex structures with tighter tolerances. At the same time volumes increased tenfold and average product costs reduced by perhaps threefold. It is a tribute to the skill and dedication of the designers that such an undertaking could be sustained by a relatively small workforce in comparison to our competitors.

 

Deliveries started in 1965 and continued until it was superseded by the 2900 series in the 1970s. There were five sub-series - the original, E&F, A, S and T. The 2903/2904 and ME29 were derivatives of the 1900. The initial priority was to expand the FP6000 and to introduce a broad range of systems quickly. The technology chosen was a derivative of that used for FP6000. This technology was an evolution of that previously used by Ferranti and was robust and well understood. The circuits were based on the FP6000 but used more reliable silicon transistors. The PCBs were simple with two-sided tracking and without plated through holes to interconnect the sides. The logic design was done manually. The wiring design for the 1902 used a CAD system which ran on the EMIDEC 2400. The backplane was connected using direct point-to-point wiring. Wires were pre-cut to standard lengths. To make the wiring process semi-automatic, a machine presented the wiring list one wire at a time. An operator on one side of the machine inserted the wire. An operator on the other side used a jig to test that the wire had been connected between the correct pins.

 

The Original 1900 Series

The original series built using this technology comprised the 1901, 1902, 1903, 1904 and 1906 for commercial applications, spanning a wide performance range, and the 1905, 1907 and 1909 for scientific and engineering work. The scientific machines were variants of the commercial systems with added hardware for floating point operations. The larger members of the range carried different model numbers, while the smaller members just had a feature number for the added hardware. This approach to the scientific market and the nomenclature was carried forward to subsequent members of the range.

The mid-range 1904 was the FP6000 with the 1900 Standard Interface and using silicon technology. The 1906 was a new design with hardware registers and additional data flow to boost the performance to some 50% higher than the 1904. A variant with a faster store gave a further 35% performance boost. The 1903 was a simplification of the 1904. Extracodes were substituted for expensive hardware operations, and smaller configurations were supported to give performance about 40% that of the 1904. The 1902 was a 1903 with a slower store and performance about half that of 1903. The 1901 used a serial/parallel data flow with performance 50% of the 1902.

 

 

System

First Del.

Proc.

Clock ns

CORE store

I/O

Cycle us

Size KWs

Max no of Channels

Est. Max Rate kch/s

1907 (1μs)

1967

750

1.1

32-256

no limit

3200

1906 (1μs)

1967

750

1.1

32-256

no limit

3200

1907 (2μs)

1967

750

2.1

32-256

no limit

2000

1906 (2μs)

1967

750

2.1

32-256

no limit

2000

1909

Aug. 1965

1000

6

16-32

23

 

1905

May-65

2

16-32

23

264

1904

1965

2

16-32

23

264

1903

Jul-65

2

8-32

8

340

1903 EMU*

2

8-32

8

340

1902

1965

6

4-32

8

220

1902 EMU*

6

4-32

8

220

1901

Sept. 1966

4000

6

4-16

6

220

*EMU = Extended Mathematical Unit

 

Peripherals were in general connected via the 1900 Standard Interface. This made it possible to separate the development and lifespan of the peripherals from the processors and to use them on every machine in the range. Early systems offered a comprehensive range of peripherals with the exception of exchangeable discs. Many of these had long lives and continued in active use over several processor generations. Punched card readers and punches were ICT designs drawing on the company's traditional skills in card equipment. The 80-column card punch used a mechanism which was essentially unchanged from its design in 1910. The printers were also ICT designed and built. Tape transports came from a variety of suppliers including DRI (UK), C des C (France) and CDC (USA). Manufacturers of drums and fixed disc stores included Data Products and Bryant. Exchangeable discs, introduced about 1966, were from CDC and DRI.

The E/F Series

 

 

First Del.

Proc.

CORE store

I/O

System

Clock ns

Cycle us

Size KWs

Max no of Channels

Est. Max Rate kch/s

1907 E/F

1968

750

1.8

32-256

 

2400

1906 E/F

1968

750

1.8

32-256

 

2400

1905E

1967

750

1.8

32-128

 

1200

1905E (H/W Registers)

750

1.8

32-128

 

1200

1905F

750

0.75

32-128

 

1200

1904E

750

1.8

32-128

 

1200

1904E (H/W Registers)

750

1.8

32-128

 

1200

1904F

750

0.75

32-128

 

1200

 

The first development was the E/F series - the 1904E, 1905E, 1906E, 1907E and the similarly numbered F machines. It used the same technology as the original 1900s with several architectural improvements. The extended addressing modes introduced with the 1906 were applied to the upper half of the range, allowing programs (and their data) larger than 32K words, reinforcing the requirement for the larger physical stores which were offered.

 

Dual processors were introduced.  The 1906E was a dual 1904E which provided increased throughput compared with the original 1906 with the additional benefits of resilience against CPU failure and the ability for customers to upgrade from installed 1904Es. A 1904E was used to develop the 1900 paging feature which was incorporated in the large A‑series machines.

 

The E/F series was a mini-range centred on a single design core. Variants included optional hardware registers for the accumulators (20% performance gain), alternative stores of 1.8μs and 0.75μs (the difference between E and F worth about 25%), a floating point unit and dual processors as mentioned above. The economies in development of this approach yielded benefits in price and timeliness to market.

 

Evolution of internal control

A processor typically has to perform a sequence of internal operations in order to obey an instruction in a program. During each step in the sequence it is necessary to tell internal controls what action to take. There are typically hundreds of internal controls and their operation will depend on factors like the type of program instruction, its position in the sequence and the results so far. The implementation of these control mechanisms is a crucial part of the overall design, strongly influencing speed and cost. They can easily occupy as much as half the processor logic.

 

There are two main types of control schemes. In a hardwired scheme the sequences and derived controls are implemented using the standard logic family. Optimisation techniques can reduce the size, but often at the expense of increased complexity. The "microprogram store" approach regularises the controls into a single store analogous to the storage of instructions in a program.

 

The early machines used discrete component logic which was relatively expensive. Designing a specialised fixed store was good value where there were large numbers of controls as in the 1906/7 and the E/F series. The 1906/7 used a classical bit-mapped approach where controls are mapped directly to bit positions in the microprogram word (96 bits wide in this case).

 

The E/F series used a coded approach where fields in the microprogram word controlled groups of actions. The E/F store was 48 bits wide.

 

The A, S and T machines used Small to Medium Scale Integration (SSI/MSI) integrated circuit families. They offered cheaper logic but did not provide any fast and cheap storage components so it was more cost effective to implement hardwired control in those machines.

 

By the time of the 2903 and ME29, integrated circuit technology could provide memory components to hold microprograms. Their relatively low cost allowed large microprogram stores and they had the great benefit of being soft-loadable. This allowed a blurring of the distinction between low-level control microprogram functions and parts of the Executive functionality. This was used to great effect in such areas as the 2903 Direct Data Entry feature.

 

The 1900 A Series

 

 

First Del.

Processor

Clock ns

CORE store

I/O

System

Cycle us

Size KWs

Max no of Channels

Est. Max Rate kch/s

1906A

1970

100

0.75

32-256

 

6500

1904A

1969

500

0.75

32-128

 

3000

1903A

1968

720

1.5

16-64

12

600

1903A SCF†

1968

720

1.5

16-64

12

600

1902A

1968

1500

3

8-32

8

520

1902A CCF‡/SCF†

1968

1500

3

8-32

8

520

1901A

1969

 

4

4-16

 

220

1901A CCF‡

1969

 

 4

4-16

 

220

‡ CCF= Commercial Computing Feature (Group 4 instructions- Fixed Point Multiply/Divide and I/O conversion)

†SCF= Scientific Computing Feature (Group 13 FP instructions – held FP Accumulator)

 

The 1900 A-series machines were a landmark as they marked the move to integrated circuit technology. By the time of their design there were two integrated circuit families with the speed required to meet the needs of the 1900s. The TTL family was pioneered by Texas Instruments and subsequently taken up by many semiconductor companies. Stevenage led the early ICT work with an experimental TTL 1900 built in 1966. Motorola had been developing the MECL2.5 range. Manchester engineers developed a novel way of using these circuits and collaboration between ICT and Motorola led to the development of the Motorola MECL10k range which was still being made in 1996.

 

The speed and small size of ICs forced a fundamental re-examination of the whole packaging technology. Two approaches were developed. For TTL, a modular approach to PCBs was adopted with four different board sizes. Much of the interconnection moved from the backplane to tracking on the PCB. The benefit was increased speed. The disadvantage was that there were now many board types to design and support. PCBs were four layers and had plated-through holes. The backplane was wrap-wired. For MECL10k the interconnection used "series matched transmission lines". One or two ICs were mounted on plug-in cards which contained the series matching resistors. The plug-ins were interconnected by a multi-layer platter which matched the transmission line.

 

The handling of the complexity of the new technologies was made possible by equally significant advances in design tools. Particular mention can be made of the tracking system used to route interconnections in the platters automatically. Handling the multi-layer boards demanded a massive jump in manufacturing capability so the PCB plant in Kidsgrove embarked on a series of process developments and investments which moved it into world-class, a position it has continued to maintain. Computers that used ICs were termed "Third Generation". ICT was among the first companies worldwide to adopt these IC technologies and turn them into products with the A-series which had the effect of moving the 1900 technology base from conservative to leading edge. TTL technology was used for the 1901A to 1904A. The fast but more expensive MECL10k was used for the 1906A.

 

All machines had optional floating point capability. The 1904A and 1906A had a paging capability and optional High Speed Mode I/O channels which were used to attach fast drums for this purpose. The 1902/3A machines were one processor with different stores. The 1902A used cheaper timing circuits and ran at a slower clock rate. The 1901A used a new compact design incorporating a printer in the same housing as the processor. It had a new, low cost Twin Exchangeable Disc system. To optimise performance the 1906A used a system of asynchronous timing in which the internal beat rate of the machine changed according to the operation it was performing.

The 1900 S Series and 1900 T’s

 

System

First Del.

Processor

Clock nS

 

Store

I/O

Speed uS

Size Kws

 

Max no of Channels

Est. Max Rate kch/s

1906S

1973

100

0.3

32-512

 

11000

1904S

1972

300

0.5

32-256

 

5000

1903S

1971

640

1.5

16-128

18

1400

1903T

1973

 

0.8

32-128

 

2500

1902S

1971

1500

3

16-64

 

1100

1902T

1974

1000

3

16-64

 

830

1901S

1971

 

4

8-16

 

235

1901T

1974

 

4

16-64

13

630

 

The S-series was the last to span the entire 1900 range. By the time of the T-series the larger machine requirements were being fulfilled by the new 2900 range. However as 2900 was being introduced with the larger models first, the lower part of the 1900 range continued to sell and was refreshed by the T-series. The S-series was a comprehensive upgrade across the range. The enhancements were all evolutionary but significant in their scale. The 1906S received a spectacularly fast store made by Plessey using plated wire technology and cycling in 250ns, more than twice the speed of previous stores, which gave it a 40% performance uplift. The 1904S made selective use of the new, faster Schottky STTL logic for a 30% performance gain. The 1903S had extended store capability and a fast peripheral scheme with more Standard Interfaces. The 1902S and 1901S grew their configurations and their throughput.

 

The purpose of the T-series was to keep the lower members of the range competitive. Performance upgrades were achieved by regrading higher machines; the 1903T was based on the 1904A and so on. All machines had semiconductor stores. The 1901T and 1902T had Integrated Disc Controllers to reduce costs and floor space.

 

The 2903 Series

 

The 1900 machines were positioned as what we today would call mainframes.

ICL was determined to enter a rapidly growing new segment characterised by companies which were too small to have a DP department. Computing needed to be made simpler. The 2903 range and ME29 range were developed for this segment. A robust but inexpensive architecture was needed and the elegance and simplicity of the 1900 architecture fitted the bill well. The naming, market positioning and projection of the machines distanced them from the 1900 range. From a customer viewpoint they were not 1900s. However, from an architectural and engineering viewpoint it is clear that under the Hot Tango skin there beat a 1900 heart.

 

The 2903 employed an evolution of the TTL technology used in the A-series. Semiconductor store components were just becoming available from Intel and it was decided to exploit them with a soft microprogrammed design. The 2903 was one of the first machines in the world to use this technology, as we became painfully aware when Intel ran into difficulties - truly the "bleeding edge". The 2903 innovations were formidable including a semiconductor main store, a semiconductor control store addressed as part of the main store, a video console compared with the teletype console of the 1900 range, Direct Data Entry in parallel with other operations, new Fixed and Exchangeable Discs, a new shape and the 2900 colour. And it was an overnight success. Later the 2904 provided a twofold power boost. The 2903 was designed with data routes capable of upgrading to eight bits for compatibility with 2900. An experimental 2900 version was developed at Dalkeith but did not go into production.

 

System

First Del.

Processor

Clock nS

 

Store

I/O

Speed uS

Size Kws

Max no of Channels

Est. Max Rate kch/s

2903/25

May-76

540

1.14

Up to 64

 

 

2903/40

Mar.-74

540

1.14

Up to 64

 

520

2904

May-76

540

1.14

Up to 96

 

 

ME29

1980

 

 

 

 

 

 

The ME29 succeeded the 2903 and was also a soft microprogrammed machine. It resulted from collaboration with Palyn Associates on an emulator known as Emmy using MECL technology. The model 35 had similar performance to 2904 while the 45 was 80% faster.

 

The 1900 range was sold over a period of more than a decade from 1964. The architecture continued in the 2903 and ME29 ranges, extending the total lifetime to some 25 years. 30 years on, orders were still being taken in 1997 for 1900 applications to run on Series 39 machines under the CME* operating system. The range was undoubtedly a success story for ICT and later ICL. While many people and groups contributed, its success owes a great deal to the skill and dedication of engineering teams throughout the company. The hardware and software product engineers, tools and support engineers and manufacturing engineers created and sustained a complete range. And they did it with a fraction of the resources employed by our main competitor.