Microprocessor History
Foundations in Glenrothes, Scotland

Jim McGonigal


It is widely accepted that a small company in California called Intel developed the world's first microprocessor in 1971. In the late 60s and early 70s there was significant interest from calculator companies to further reduce the size and cost of desktop calculators, and to create a new market for personal calculators. Calculators had for some time used discrete transistors, and latterly discrete logic and custom MSI ICs, but a single chip calculator was only a vision. However, there was another microprocessor development happening in Glenrothes Scotland, also designed for the burgeoning calculator market which may have beat Intel to the market, both in timing and performance.

Toshiba Model from 1969

Disassembled Calculator

100 MSI ICs and 82 Transistors

Elliott MOS Research Laboratory 

The Formation of Pico Electronics Ltd

Elliott Automation was a significant British computer maker who in the 1960s realised the need to progress its own semiconductor technology. In 1966 the company established a facility in Glenrothes to manufacture Resistor-Transistor Logic and Diode-Transistor Logic , followed by the establishment of a MOS research laboratory. Geoff Brookes, Alan Strath and George Stevenson relocated from Borehamwood to Glenrothes to establish the MOS facility
(1). One of their first tasks was to produce an 8-bit computer using MOS technology, with George as the computer expert. In 1967 Elliott Automation merged with English Electric, and when GEC bought English Electric in 1969 they decided to close their production plant in Glenrothes.
Alan Strath had predicted the closure in 1967. "Since English Electric had recently completed a new microelectronics factory in Chelmsford, Essex, we expected that the Glenrothes facilities would be closed, so we successfully offered our services to General Instrument to establish a new facility". The Glenrothes facilities were complemented by the Hughes Aircraft factory that had been established in 1960 to produce germanium and silicon diodes and transistors, before moving into MOS design and production during 1967/1968.

In the summer of 1970 four General Instrument design staff  left to form Pico Electronics Ltd. They were George Stevenson, David Campbell, Harry McLennan and Les Leech. George was the Director of Engineering and the others were young, bright designers. All had previously been at Elliott Automation. Moses Shapiro, the CEO of GI advanced some startup capital on the basis that GI would get exclusive rights to the manufacture of  the single chip calculator ICs that the new company were planning to develop. They set up in a rented office in the Postgate in Glenrothes and very quickly put their design ideas into practice. The team already had a significant legacy in successful calculator chip design with one of the last jobs they had completed in GI being a five chip set for a Facit calculator. The team had designs for calculators going back to the Elliott days for Bell Punch.

Location of Pico's First Design Office


David Campbell remembered the first IC development at Pico Electronics.

"We were certainly not aware that any other company in the world was working to develop a single chip calculator at that time.  George Stevenson was the project leader and it was he who came up with the advanced and novel architecture used in that first calculator chip. I have always admired that achievement and give him full credit for it. The other guys, myself included had the job of converting his design ideas to a working chip using a 4 mask 10 micron metal gate PMOS technology. My own contribution was the design and layout of the program ROM and the dynamic RAM memories and the timer. This first machine was really advanced for its time, because it was a Reduced Instruction Set (RISC) processor. For example an 8 bit floating point addition of 2 numbers required just one line in the ROM. The whole program for the calculator was only 70 lines of ROM. The ROM was wide to allow the different parts of a calculation to be done in parallel. This meant that although the clock speed of the ROM was very low, the time to perform calculations was much quicker than other calculator chips which emerged in the years after our chip. The layout of the chip was done by hand because there were no software design tools for layout at that time. The layout was done by drawing the 4 layers of the PMOS transistors at 500 X scale onto a stable mylar film with a grid pattern. The transistors were represented by rectangular boxes for the drain, source,  gate and contact,  and the metal interconnection layer was drawn as rectangular lines.   There was also no computer simulation of the design prior to layout. To prove the design concept we built a fully functional but not very reliable breadboard using off the shelf  TTL logic chips soldered onto a number of stripboards which were just connected together by wires."
David Campbell continues. "The Pico calculator chip had stored program memory in the form of a ROM which worked in the same way as the ROM inside a microprocessor to perform a series of pre-programmed instructions. Remember in those days there was no OTP which could allow a microprocessor chip to be re-programmed. All the initial single chip microprocessor applications had hard wired mask ROM code. Applications which used external ROM or RAM for program memory and scratch pad memory were not single chip applications". Re-programming was still possible through a change in the ROM mask.

The design was completed very quickly and fabbed at GI's facility. David remembers the fab cycle time being a few weeks. GI's process in those days was state of the art and the design worked very early on. By the end of 1970 they had working silicon and a working calculator prototype to demonstrate to potential US and Japanese customers. Very quickly the Monroe Calculator Company (Litton Industries) of New Jersey became Pico and GI's  first major customer of  the IC in early 1971. Pico also designed the styling and all the electronics for Monroe's consumer models. Later in 1971 or 1972 Clive Sinclair also used Pico's chips  in his calculators Sinclair Calculators. (Alan Strath remembers Clive Sinclair visiting GI in Glenrothes not knowing anything about the technology, and two weeks later he was back, an expert !)
Intel announced their 4004 microprocessor in November 1971 Intel 4004 Website. This had been designed into a Busicom calculator earlier in 1971 but had been an exclusive design. If you compare Pico to Intel in those early days, the guys who formed Pico had significant design experience on calculator chipsets for a number of different calculator manufacturers. Their vision in setting up their independent company was to develop single chip processor ICs for calculators. Intel had a couple of designers in a new lab who happened to take on a design from Busicom. It was Busicom's idea to develop a calculator platform on which a wide range of calculators could be made. However in reality they couldn't develop follow-on machines with better capabilities, and couldn't compete with other solutions coming onto the market. It was this  failed strategy that encouraged Intel to seek alternative markets for their device. Calculators were becoming the largest single market for semiconductors and attracting increasing competition.

Busicom Calculator CCA With Intel Chipset

Royal Digital III With Pico/GI Chip from 1971

Texas Instruments had also been designing more integrated versions of their ICs for calculators, however they were behind Pico. David Campbell remembered visiting TI in Houston after the Pico chip had been in production at GI for some time.

"I remember visiting TI in Houston with George Stevenson in 1972 after our chip had been in volume production for some time when they told us about their one chip calculator. The chip size was huge and it was very slow compared to ours. They called a chip a "Bar" rather than a die which I thought was odd at that time. The visit was arranged by Monroe in response to TI's effort to try to replace our chips in the Monroe calculators."

If you examine Pico's patent 4,001,556 (GB version filed in March 1971, US version in July 1971) and compare with the often cited patents of Intel (3,821,715 and 3,753,011 Intel 4004 Patent Webpage) and TI (3,819,921 3,757,306), the Pico one presents a strong case. Both the Pico and second TI patents are the only ones to make claims on single chip devices but Pico's pre-dates TI's and is more integrated, having the processor on chip with ROM and RAM. Much later on, TI invested a huge amount of effort to get Michael Cochran and Gary Boones' patent 6650317 filed which must have been in response to the claims of Gilbert Hyatt on the invention of the microprocessor. The patent is incredibly well researched and cites a massive amount of prior claims and publications including George Stevenson's "Single Chip Calculator" and "documents produced as exhibits to the deposition of George Earley Stevenson".

             TI's single chip calculator                                                                gi logo

Michael Cochran and TI's Single Chip Calculator                              GI Manufactured and Marketed Pico's Chip Designs

George Stevenson and his team moved on to more complex chips including a single chip scientific calculator and went on to design all of GI's calculator chips. Pico eventually moved from the rented office in the Postgate to the vacated Elliot Automation MOS Laboratory building on the Eastfield Industrial Estate. Pico Electronics Ltd is still in existence as part of X10 Ltd. David Campbell and Pico continued to produce a number of innovations including the de-facto X10 standard for Home Automation. George Stevenson and Les Leech are still at X10 in Hong Kong. Further Pico and X10 history can be found at Pico and X10 History. Pico Electronics still own the Elliott building, however most business is now operated out of Hong Kong. Until his recent retirement, Harry McLennan still worked at Pico in Eastfield. Another early Pico employee, Dave Thompson who worked with David Campbell on the first X10 automation chips is still at Eastfield. David Campbell has been an independent IC design consultant for a number of years.
General Instrument in Glenrothes continued to produce a number of Pico's calculator IC designs and other consumer chips including the X10 ICs. GI eventually moved their US Hicksville NY facility to Arizona, from which they spun out the PIC microcontroller business into Arizona Microchip in 1989. The GI wafer fab in Glenrothes still operates as an independent wafer foundry.

(1) Alan Strath remembers, "I joined Elliott Automation in 1965. We started up in Scotland in 1966 and I think the EE takeover was in 1967.
We started with GI in the same year, with temporary accommodation  in two adjacent Glenrothes Development Corporation terraced houses in South Parks road. George and some of his recruits worked on designs on the ground floor while we pursued the conversion of a standard advance factory as a semi plant and ordered equipment. The Daily Express printed that the MD shared a bedroom in the house with his secretary ! I believe that GEC took over EE in 1968 or 1969, although I'm not sure. As you may know, Elliott Auto had taken a licence with Fairchild,  initially for DTL. During this period we met Robert Noyce, CEO of Fairchild and Gordon Moore, R& D manager. They left Fairchild saying that it had mushroomed out of control.
The production unit at Queensway closed in 1968 or 69 and partially moved to the R&D factory at Eastfield (now Pico)."

An interesting if trivial footnote is that the Elliott Automation production facility was established in part of the Cadco "pig factory" in Queensway Industrial Estate. Cadco was an investment by the actor George Sanders. Sanders was well known for playing the "cad" in films, and in a remarkably ill-conceived business venture in the early '60s, having always harboured dreams of becoming a tycoon, threw his name and most of his money into a sausage-making scheme that went belly-up, taking his company, Cadco Ltd., with it. He was ruined financially and barely escaped prosecution.

This article was originally written by Jim McGonigal and posted at his Web site located at http://www.spingal.plus.com/micro/. It has been posted in this Web site with the permission of its author.



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