What software could you hope to run on this sort of machine? The answer was a BASIC interpreter written to fit into only 3Kbytes so that a 4Kmachine would just have room to run a program. This was loaded from cassette and could save programs back to cassette.
There was also an assembler/editor and some very simple games such as Star Trek - a character based game played on a grid much like battleships. While the rest of the world was working with Microsoft Basic the UK had already struck a blow for freedom by mainly using SWTP Basic!
An original SWTP ad - click to enlarge.
The system grew from a simple cassette based machine to one that had disk drives - and disk drives need an operating system.
Again the UK opted for something other than the standard. SWTP standardized on an operating system called Flex produced by a little known company called TSC. Flex used an elegant design and was easy to use. The first version used a linked list filing system that only used a basic directory and made sequential file reads fast. Its only problem was that the disk filing system didn’t handle direct access files at all - but in those days you were pleased to get a computer, let alone one that would let you build a database system!
Later versions of Flex solved the problem, by adding a mapping table to the front of the files, but to a certain extent its day was already numbered.
One morning the trade magazines suddenly announced that an operating system called CP/M was the standard. What they really meant was that it was the standard in the US. In the UK when a machine had disk drives it probably used Flex but suddenly CP/M became important here too and guess what - CP/M didn’t run on 6800 systems. The SWTP product was now well and truly isolated.
The momentum of the number of installed SWTP machines ensured that the UK carried on using Flex, SWTP Basic and the 6800 for some time to come. SWTP even set up its own factory in Peterborough and switched to supplying completely built units to order. Its next generation of machines were based on the 6809, a hybrid 8/16-bit processor.
The final round of machines incorporated memory bank switching and a new operating system called UniFlex, a completely rewritten operating system modeled on Unix. The machine was beginning to look like the minicomputers of the time.
For example its hard disk was a 10” model built into a case the size of a blanket box and too heavy to be picked up by one person.
By this time SWTP was no longer of interest to the hobby market or the professional market. The hobby market had cheaper and more fun machines to occupy itself and the professional market was beginning to benefit from the mass production of CP/M machines imported from the States.
The SWTP machine may have been an imported US design but ironically it isolated the UK and produces an individual market identity both for hardware and software. After the initial seed the UK more or less went off at a tangent, largely ignoring although occasionally worrying about what the US was doing. Without SWTP we probably wouldn’t have had a home computer industry in the 80s and no home computer boom.
Gordon Bell is responsible for many things, but the design of the most successful range of minicomputers, the PDP range, is probably the thing he is best known for. This is a story about when computer [ ... ]