CP/M relies on having a full 64k of clear RAM so it is completely incompatible with the Nascom system of “punching holes” in the memory map for video mapping and EPROMs. Consequently, although it was possible to use CP/M on a Nascom system, it wasn’t the most popular way to use it. CP/M was also an expensive route to take! It also made your Nascom incompatible with all Nascom software – you had to start again. However, the Gemini system was intended to run CP/M right from the start.
Initially CP/M 1.4 was available for modified Nascom-2 systems using the Lucas disk system. The Nascom-1 wasn’t a good candidate for disks (although some people managed it).
A special EPROM (either RP/M or SIMON) was used to start the system on the G811 and GM813 CPU cards. This was paged out of memory during the boot process, leaving blank memory for CP/M.
Various versions of CP/M-80 (Version 2.2) were available for the Gemini machines.
GM512 – For Multiboard with GM815 350k/drive
GM513 – Suitable for Nascom with GM809 controlling GM815
GM532 – For Multiboard with GM825 800k/drive
GM555 – for GM849 with BIOS 3.4 or later or GM849A with BIOS 3.5 or later
QDDS format (Quad density, double sided, 96tpi for the base drive)
GM578 – A version of CP/M-86 for systems using the GM849 with the GM888 8088 processor board was also available.
GM815(?) – for GM849 with BIOS 3.4 or later or GM849A with BIOS 3.5 or later
DDDS format (Double density, double sided, 48tpi for the base drive)
Suitable for GM815 drives
nascom.info 