Ex-IBM staffer Peter Plinston formed Positron Computers in 1979 along with Peter Loftus (also ex-IBM) and Edward Ellis, Peter had designed a single board computer based around the Motorola 6809 CPU and had already received sponsorship from glass makers Pilkington Glass. In 1982 new government initiative called the National Enterprise Board started up with the aim of funding local businesses. The provided an extra £265,000.

The two Peters (pictured above) were joined by Simon Peacock on the software side of things. Soon after, Ron Murphy joined as hardware engineer. Their machine was called the Positron 9000 and it ran the unix-like OS9 from Microware. It was aimed at local schools initially because that was the government drive at the time.

The resulting machines were pretty unique in that they were truly multi-user and the only example of a Motorola reference design that used Motorola 6829 MMUs to accommodate up to 32 users on serial terminals, 4 per MMU.

OS9 is an environment that provides each user their own memory space but with shared executables, so if multiple users were running (for example) BASIC09 there'd be one copy of the executable in RAM and each user would have their own reserved memory to use. When the last user exited, the executable would be removed from RAM. The entire OS is on 5 2764 ROMs, so the external floppies and 5MB hard drive were for userspace programs, though obviously booting from either was supported. The storage hooked up via the GPIB port on the back of the machine and each storage module was given its own address.

Over to Simon:

"Peter (the owner of Positron) seemed to do most of the fault-finding by touching a chip and seeing how hot it was. In the early days, we had an oscilloscope before moving on to a logic analyser and ending up wit an in-circuit emulator. We worked closely with Microware and had visits from Ken Kaplan and Larry Crane a couple of times. They liked what we were doing with the MMU, although that was problematic since supplies from Motorola were very scarce. From memory, most systems were sold to a call logging company and a CNC company for use in their own systems. A college (Llandrillo) bought a large multi-user system that had 8 9000/4 boards in it for use by the whole college. It was also used by Channel 4 as the basis of their teletext service."

A little company history from Ron:

"Positron was registered in 1979, but as far as I'm aware the first offices were on Haydock Lane, WA11 9XS, as in the pic attached. Simon joined them here, and I did too, not long after Simon. At the time there was Peter Plinston, the originator of the systems, and Peter Loftus, Sales, both ex-IBM. Peter Loftus was listed as one of the original members. The company later moved to the industrial estate in Earlestown.
 
I joined on 2 November 1981 after completing my PhD, on multiple-processor systems. My role was hardware development and production, so both Simon and I basically assisted Peter Plinston. As I joined the two Peters where getting in samples of cases, and as some were dreadful, the big off-white monster you now have was the best of the lot. Can't remember the supplier, but it always had problems with the finish. Around the same time we were trying various hard drives and floppy drives.
 
With the move to Earlestown and the addition of more people the 9000 desktop format was being sold into some university/college departments, while the metal case systems went to industrial applications, such as Datapulse, which you already know about.
 
The IBM-PC killed any prospect of this line continuing. Though OS-9 was a decent OS, the commercial preference was for the PC - which resulted (in part) with Peter Loftus leaving to form his own business based on spreadsheet and accounting systems on the PC. By 1984 Simon and I had decided to leave and form Mentat Systems Limited."

Thanks, Simon and Ron!

Positron 9000, ostensibly a Teletext authoring single user machine.
Positron 900, multiuser business/scientific machine with two 68B09E CPUs

Positron 9000 OS9 ROM images, 5x Fuji MBM2764.
Positron 900 ROM images, bespoke data logging software, 5x Mitsubishi 2764.
Positron 9000 PCW Benchtest review, page 1, 2, 3, 4, 5, 6, 7
Press release detailing the NEB's involvement with Positron.
Advert-style newsletter listing the benefits of the 9000/4 board.
A Brochure for the Positron 900 range.
News! from Positron.
Advert for the Positron 900.
Microcomputer Development Systems brochure featuring Mr Peter Plinston himself.