inMOS and the Transputer

🌈 Abstract

The article discusses the history and development of the inMOS company and the Transputer, a unique microprocessor architecture created by the company. It covers the founding of inMOS by Iann Barron, the creation of the Transputer and the accompanying Occam programming language, the challenges faced by inMOS in establishing a semiconductor fabrication facility, and the eventual decline and sale of the company. The article also explores the lasting impact of the Transputer design and its influence on subsequent interconnect standards and processor architectures.

🙋 Q&A

[01] inMOS and the Transputer

1. What was Iann Barron's background and how did he become interested in computing?

• Iann Barron was born in 1936 in Watford, UK. At age 16, he read a news article about computers and realized that computers would be his future. He wrote to Lord Halsbury at the NRDC, who invited him to the NRDC offices and suggested he go work at Elliott Brothers, an early computer company.

2. How did Barron's early career at Elliott Brothers shape his path?

• Barron worked as a programmer at Elliott Brothers, where he proved his programming skills by rewriting a paper tape punching and conversion program to run at twice the speed. He continued to work at Elliott Brothers during breaks from university.

3. What led Barron to found his own company, Computer Technology Limited (CTL)?

• After being asked to build yet another high performance computer at Elliott Brothers, Barron suggested the company license the DEC PDP-8 instead. When the company refused, Barron quit and started his own company, CTL, in 1965.

4. What were the challenges faced by CTL, and how did Barron's focus shift to microprocessors?

• CTL's first computer, the Modular One, did not do well in the UK market dominated by DEC. To keep the board happy, the financial director was cooking the books. When Barron brought this to the board's attention, he was fired. Barron then spent time learning about the newly emerging microprocessors.

[02] The Transputer and Occam

1. How did Barron's expertise in microprocessors lead to the creation of the Transputer?

• Barron organized a panel on the future of computing for an IFIP conference in 1977, where he met Richard Petritz. Petritz proposed starting a new semiconductor company, which led to the founding of inMOS in 1978 with funding from the UK's National Enterprise Board.

2. What were the key features and design choices of the Transputer?

• The Transputer was a unique processor architecture that combined RISC and CISC elements. It had an integer processor, on-chip static RAM, four bidirectional serial links for communication, a memory interface, real-time process scheduling, and in later models, an on-chip floating point unit. It was manufactured using CMOS technology.

3. How did inMOS develop the Occam programming language to support the Transputer?

• Occam was a parallel-first, imperative programming language developed by David May and others at inMOS to take full advantage of the Transputer's architecture. It featured constructs for parallel and sequential execution, as well as message passing through named channels instead of shared memory.

[03] Challenges in Establishing Semiconductor Fabrication

1. What were the difficulties faced by inMOS in setting up a semiconductor fabrication facility in the UK?

• The UK lacked a rich pool of talent for building semiconductor fabs, unlike the US. There were also tensions between the US and UK branches of inMOS, with the US branch taking over management of the UK fab despite issues caused by the local water supply.

2. How did the financial challenges impact inMOS's operations?

• The sharp fall in the value of the pound further strained the company, even as it struggled to keep its RAM chip business running and continue the Transputer research and development.

[04] The Rise and Fall of the Transputer

1. What were the different models of Transputer chips released by inMOS, and how did they evolve over time?

• inMOS released several Transputer models, including the 16-bit T212/M212, the 32-bit T414/T424/T425, and the T800 series with an on-chip floating point unit. The chips were available in different clock speed variants and featured improvements in on-chip RAM and other capabilities.

2. How was the Transputer used in various systems and products?

• Transputer systems were often used as coprocessors or accelerators, with the Transputer handling specific parallel workloads while a host machine handled other tasks. Transputer-based products included add-in cards for PCs and workstations, as well as the ill-fated Atari Transputer Workstation.

3. What led to the decline of inMOS and the Transputer?

• As the Transputer became less competitive against other processors like the Intel 80386 and Motorola 68030, inMOS's memory chip business declined. The company was eventually sold to SGS Thompson, who attempted to redesign the Transputer but ultimately failed to revive it.

4. What is the lasting impact of the Transputer and inMOS?

• While the Transputer itself did not achieve widespread commercial success, its interconnect technology became the basis for the IEEE 1355 standard and later influenced the development of standards like HyperTransport and PCI Express. Former inMOS employees also went on to found companies like XMOS, which continue to explore multicore and parallel processing architectures.