The UK 1970s Big Board Computers
The UK 1970s Big Board Computers
Written by Historian   
Tuesday, 17 July 2012
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The UK 1970s Big Board Computers
Naked PCBs


At the time the growing home computer market was still lead by the electronics enthusiasts. Most of the information to be had was in magazines like Electronics Today International (ETI) - simply because there were no computer magazines. The first UK computer magazine, Personal Computer World (PCW) appeared in 1978.

There were various “build-it-yourself” projects and many of these made it into commercial production. The philosophy was that you could soften the blow of buying a full system by breaking it down into little bits. You bought the components for the processor card, then the RAM then some I/O and put it all into a box and you probably ended up spending as much as a commercial system but you didn’t notice.

As electronics progressed things became cheaper and there came a time when a different approach was possible. Instead of breaking the system into little bits and joining it together using an expensive system bus you could do the same thing for less money by putting it all onto a single PCB. By eliminating the components needed to implement an external bus and all of the interface devices needed to connect each module you really could build a low cost machine.


The first and most successful of the “big-board” computers was the NASCOM 1. The project started in the summer of 1977. Although the company selling the NASCOM 1 was Lynx Electronics, the UK subsidiary of North American Semiconductor (NASCO) the design was subcontracted to Shelton Instruments a London based company.

John Marshall, head of NASCO, had noticed that the UK wasn’t really well served by the higher priced US products and had decided that a special product was needed. The NASCOM 1 was based on the Z80, mainly because Mostek provided a lot of free help for the project and it was targeted to be less than £200 ($300)  and usable.

The machine took the form of a single large PCB which contained the Z80, 1Kbyte of EPROM, and 2Kbytes of RAM. What made it special was that for not much more than a price of a microprocessor trainer it included a TV display and full keyboard.

Admittedly the TV display used 1Kbyte of the RAM to hold its 48 character x 16 lines output but it was cheap and you could actually make it do something. Soon there was a 2Kbyte Basic interpreter, a 4Kbyte Basic interpreter, an editor/assembler called Zeap, a letter editor written by ICL and even a CP/M based floppy disk system.





You could buy a case for the NASCOM and for the many similar systems that followed but most users simply “nailed” the PCB to a sheet of plywood and got on with using it!

In the USA the same trend toward single board machines resulted in the Apple II but it certainly wasn’t just a PCB nailed to a block of wood. At the same time that the Apple II was gaining ground in the states budget machines costing about a quarter as much were the staple home computer in the UK.

The NASCOM 1 lead on to the NASCOM 2 but before that there was the Ohio Scientific Superboard (6502) which was quickly copied as the UK101 (6502), The PowerTran PSI Comp 80 (Z80), the Triton (Z80) the Tangerine (6502).





The number of one-board computers being developed at around the £200 ($300) marked the start of the personal computer revolution in the UK, even to the extent that the general press and TV started to run stories about the “computer craze” that was sweeping the nation.

The one-board computers started the move away from kits that only the electronics enthusiast would consider building to machines that could be bought for the fun of programming or even for the fun to be had running programs. For example the UK101 came complete with 8K Microsoft Basic in ROM. You simply added a TV set and cassette recorder, switched the machine on and started programming.

The mystery of these later machines is why they continued to be sold as naked PCBs?

For a few pounds more the manufacturers could have put them into pretty boxes and had a low cost competitor to the Apple II or the Commodore PET which where both on the market at about the same time. I can only speculate that to be recognized as a low-cost computer a product had to look as unadorned as possible. Another reason may have been that to start a company building a PCB based computer didn’t take much investment but the cost of manufacturing a box to put it in raised the stakes too high!

What is clear is that the number of single board computers that were designed and built in the UK at the end of 1979 created a market quite unlike that in the US. With lots of small companies with experience of designing personal computers it was inevitable that each one would attempt to design a mark II to capture a share of a market that was about to go from rapid to explosive growth.

The next round of the revolution was about to begin and this time the products would have boxes to live in!



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