UK micro pioneer Chris Shelton: The mind behind the Nascom 1

Massively parallel processing

The whole thing was built out of some 90,000 transistors, a fraction of the number found in rival CPUs: the PowerPC 601 had a million, the Pentium three million. The die was a mere centimetre-squared in area. Today, Shelton reckons, even fabbed using CMOS rather than bipolar, it would be barely a millimetre in size yet capable of clock speeds of many gigahertz. With so few transistors - in chip terms - yields would be in the order of 95 per cent, he claims, and so the cost of each chip “next to nothing”. It would be so economical and consume barely any power that it would be cheap to implement large arrays of chips operating in parallel. “It would find a huge home in internet nodes managing internet traffic at blazing speeds.”

Arrays, because Sinclair had always been keen on the potential of parallel processing - “Clive was always keen on arrays; parallelism as a way to bigger things was always part of his thinking” - so Shelton had designed the PgC7000 with processor-to-processor communications in mind. The PgC would ultimately form the basis for the massively parallel computers-on-wafers that Sinclair’s ill-fated wafer-scale integration endeavour, Anamartic, would produce. In part, that’s where the notion of the core reading a buffer independently filled by the memory controller had come from: “You could squirt masses of data from one processor to another at the RAM-RAM level. You could construct a matrix of channels all running at blazing speeds Ram to Ram with no processor downtime,” says Shelton.

Parallel systems would require a smart OS. Fortunately, Shelton had found one: TAOS from Tao Systems, “a wacky bunch of people” he had discovered when searching for emulation software. TAOS was a microkernel-based hardware-independent, object-oriented OS with multi-threading, asynchronous process-process messaging and load-balancing. It could have been made for the PgC7000. Indeed, Shelton tweaked the 7000’s instruction set to better support TAOS.

The prospects for the new processor looked rosy, and Sinclair formed a new company in 1991, PgC Ltd., to sell it. Now upped to 250 MIPS, the chip would go on sale as the PgC7600. It would cost $100 in quantity. PgC also announced a cheaper version to help get the chip’s foot in computer makers’ doors: a $40 part fabbed using CMOS technology and thus only capable of 80 MIPS - still impressive compared to the competition.

Ahead of its time

PgC promised it would have a 1000 MIPS CMOS part, the PgC7700, out by the middle of 1993 and sell it for $400. A bipolar version with less on-board memory but rated at a staggering 2000 MIPS yet costing a mere $200 would follow soon after, it pledged. Handheld computers, desktops, terminals and many an embedded application would all be homes for PgC parts, the company boasted.

In Sinclair Research’s 1991 annual report, Sir Clive wrote: “PgC Ltd continues to develop its very high speed computer chip and has received an injection of capital from outside investors. Progress is very promising.” Among those putting in money was Chris Shelton himself. Most of the rest came from Sinclair.

PgC took its processor to market. Shelton recalls talking to Toshiba. “We also talked to IBM. It used the same fab for processors and Dram, so [the PgC] would have been a great product for them. They could have put down one piece of silicon with the processor and the video ram on and made a Transputer that would have blazed away and been tiny, but they were too tied to producing the PowerPC for Apple.

“We did get working silicon, that was the exciting thing. We were able to go out and sell it on the basis that we could show it working. At the time, it was one of the fastest things ever.

”I’m still excited about it... it was way ahead of its time.”

Fast but unorthodox, and PgC failed to persuade any of the big-name chip companies to buy into its processor technology.

“[Sinclair had] given it a certain budget and a certain time to prove itself. But he was quite firm: when the budget was up, the budget was up, and that’s quite right,” SHelton remembers. “I put my own money in, and so did another friend. Eventually we sold it to a company in Seattle. We got some of our money back, but not all of it.”

Too revolutionary?

In April 1994, Sinclair announced he had “licensed” the PgC design to Microprocessor Technology, inc (MTI) in Seattle, which was seeking funding to put the CPU into production. In Sinclair Research’s 1994 annual report, Sir Clive noted: “This looks highly promising, we have received a first payment of £100,000, but it is too early to make predictions.”

It was, and MTI proved unable to get the PgC to market. The powerful laptops Sinclair hoped to make with the new processor wouldn’t arrive either, and neither would his office automation systems.

Chris Shelton largely turned his back on computers. He’s long held a love of mucking about in boats, and during the late 1990s he focused his engineering skills on marine technology. He designed the “submarine telepresence vehicle” Spyfish leisure RoV for Nigel Jagger’s H2Eye to “allow you to enjoy the water without getting wet”, as he puts it. Just over ten years ago, he acquired Autonnic Research, an Essex-based firm that designs and manufactures fluxgate magnetometers used in many a ship-board instrument.

Now in his late 60s, he hasn’t stopped working. Indeed, he’s currently investigating a system to improve the performance of the power systems that need to feed modern boats’ many different devices from motors to sensors to communications kit. “I live in the future,” he says, “not the past.” ®