80-Bus News


May–June 1984 · Volume 3 · Issue 3

Page 38 of 51

The 80-BUS 800 Series

by P. A. Greenhalgh

In these hallowed pages in the past you must have come across various 800 series numbers (e.g. “I use a GM802 plus EV814.....”) and wondered what the writer was referring to. Well, fear no longer. This is the first part of an ‘article’ describing what physical products these magic incantations refer to.

So what is an ‘800 Series’ product? Well, the 800 series was started by Gemini Microcomputers some considerable time ago, and consecutive numbers were given to each product as it was developed. An 800 number is allocated by Gemini only to major 80-BUS related items, and this therefore includes all of their 80-BUS boards, power supplies, keyboards, assembled motherboards etc. All of these Gemini numbers are given a ‘GM’ prefix. Gemini also decided to include other ‘preferred’ products from other manufacturers, and therefore the ‘EV’ referred to above means that the product comes from EV Computing. Similarly Belectra, Climax Computers, IO Research, and Microcode Processes have all had 800 series products.

So what is special about 800 series products? Well basically these are all built and tested products (there are one or two exceptions, and these have a ‘K’ suffix, meaning ‘kit”), any 800 product should run with any other 800 product, and software support is available for most permutations. This is a somewhat over-simplified view, as, because of the exceedingly high number of permutations, there will inevitably be some exceptions, but for example to the question “Will a GM813+​GM832+​GM829+​GM888+​GM833+​IO828+​IO830+​EV814+​GM862+​GM825+​GM835+​GM816+​GM818+​MP840 system run, and is there software for this?” the answer would be “Yes, if you can afford it, and if you have Battersea Power Station at your disposal.”!!! However, if the question substituted that string of 800 numbers for just “GM813+​MAP256+​GM812+​Nascom-AVC” then the answer would be a resounding “NO”, as the AVC and GM812 are set to conflicting ports, the AVC memory has to overlay the MAP256, the GM813 and MAP256 have different uses of port 0FEH, etc. Now the problem is not, at the end of the day, totally insoluble, but you would have to have a very good working knowledge of all of these products, and you are certainly going to face a severe challenge in finding any software that will run straight away, even if you overcome these ‘slight’ problems.

So the point is that if you have an 800 series based system then you will certainly find life much easier if you stick with 800 series add-ons, and hopefully the following list will give you a much greater insight into what these are..... (Please note that the following information is NOT guaranteed to be correct, although it hopefully is! Contact your dealer if you have a specific requirement.)


A complete 64K twin disk CP/M computer based on a single board designed by Gemini and sold to British Micro, who later released it as the ‘Mimi’.


80-BUS 64K dynamic RAM board from Gemini incorporating Nascom style ‘page-mode’ to allow up to four of these boards to be used in a system. Also available as a kit in 16K form and minus page-mode circuitry. Does not support the ‘Extended Addressing’ mode later introduced by Gemini (see GM813).

Page 38 of 51