Many of the Gemini expansion boards were unsuitable to the NASCOM-1 due to insufficient I/O decoding on the main board. Also the lower clock speed of this machine meant that it couldn’t really be used with disk systems. However, with a bit of hardware modification and a little luck in running the NASCOM-1 at 4MHz, both these problems were solvable.
Several of the cards are coded Gnnn on the actual card, whereas they are advertised as GMnnn. This may be irrelevant, but I thought I’d better mention it. Where other codes, e.g. EV are used they are for a manufacturer other then Gemini.
The official numbering for Gemini products was GMxxx. The idea of the 800 series was that they were already built and tested, all the components would work together (in theory – it’s probably impossible to test every combination fully) and there was software support to enable them to do so. The numbers were issued in order of development.
Note that the Gemini Galaxy 2 and Quantum 2000 computers were advertised as using two Z80 processors. They didn’t happen to mention that only one was used as the system processor and the second as the graphics processor. Was this the beginning of “imaginative advertising” in computers?
I’ve included various pages of information; pictures, circuit diagrams etc. Almost all of these are items in my collection. However, there is a lot of information that I don’t have. One of the best (and only!) sites that I’ve found for 80-Bus stuff in particular is 80bus.co.uk (opens in a new window/tab) where Richard has archived some very nice stuff.
19in Frame GM610 Not intended for use with the NASCOM system as it only accepted 8 inch deep cards.
19in Frame GM656 Suitable for use with all systems.
5-Slot Motherboard GM654 Suitable for use with all systems.
8-Slot Motherboard GM655 Suitable for use with all systems.
5-board frame GM662 Not intended for use with the NASCOM system as it only accepted 8 inch deep cards.
6-Slot motherboard GM682 Suitable for use with all systems.
EPROM Board GM803 Sold without EPROMs!
(dated May 1982) 48/96TPI – replaced later by GM829. This was not suitable for use with the NASCOM-1 due to the slow processor.
GM824 A-D GM824 Re-badged version of an IO Research unit.
RAM Disk GM833 512k dynamic RAM. Virtual disk operation.
Network Adapter GM836 Adaptor for their proprietary networking system.
Colour vector graphics GM837 Re-badged version of a Climax board. 256×256 display. 16 colours. Much cheaper than the PLUTO system!
EPROM Programmer GM860 “Bytewide” programmer with built-in mains supply.
Monitor Badged 12in Phoenix unit with green or amber phosphor.
Pluto graphics card (1982) IO828 High power (for the time) graphics board. This was a basic version of the IO Research board.