The story of Lyons Electronic Office, LEO, is one of the more remarkable ones in the field of computing. Somehow, an English company that ran corner tea shops became a pioneer of business computing. This is well-documented elsewhere, and there is an organisation, the LEO Computers Society, which preserves the history of this far-sighted company. Their Web site contains lots of information about the company and its machines. More detail can also be found in the book "LEO The First Business Computer" ISBN 0-9521651-0-4.

Click to enlarge The LEO III was LEO Computers Ltd's first (and only) transistorised computer, first installed in 1962: shortly afterwards the company was taken over by English Electric Ltd. I possess a number of logic cards from the LEO III. The image shows one of them in side view: click on the thumbnail image of the card to see a larger version (61KBytes).

The card is made of brown paxolin, 9 inches by 7and 1/4 inches with the back corners removed to make a 28-way edge connector, although only strips in use are gold-plated. It has a pale blue plastic front handle bearing the LEO logo. Twelve metal tags through the handle provide test points, although not all are used on all cards. This particular card bears four Mullard OC23 power transistors, four RCA 2N1091 transistors, and four Texas Instruments 2G302 transistors, as well as Mullard OA10 diodes and Hughes HG5009 miniature diodes. The population of transistors on my LEO III cards is very varied, including many US devices. There are few of the classic British Mullard transistors like OC77, reflecting the later age of the machine compared to others for which I have cards.

I did offer my cards to the LEO Computers Society, free of charge, but I was told that they "would not be welcome" because about half of them have been damaged by someone breaking off the edge connectors for gold recovery and also removing some of the components. In view of the rarity of the cards, and the fact that half are undamaged, this surprised me, however that was their decision.

The LEO III was a successful machine with a large number of installations, and English Electric also developed another successful transistorised machine, the KDF9.