Gemini 80-Bus Resource

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HELP NEEDED!..... I am desperately seeking to archive Gemini 80-Bus software before it is lost forever. I am particularly interested in CP/M bios versions, GEMSYS and any disk images that may be around. I am also keen to preserve as much hardware as I can (finances allowing). Please get in touch if you can help or have a similar interest.

John, August 2019


This page is designed to bring all of my Gemini software and firmware into a single resource. It will be updated as more items come to light.

Disk Images

Unless otherwise stated, these disk images are raw, track interleaved images in GEMQDDS 80 track 788k format and include a 64K Version of CP/M. They can be used with CPMTOOLS and the Gotek disk emulator using the configurations detailed in the article The_Gemini_80-Bus_Saga.

System Disks and Utilities

The following system disks are based on the Gemini GM512 CP/M release. This product was CP/M Version 2.2 using Gemini Bios version 1.4. This BIOS did not support Winchester disks.

The disk includes original files supplied by Gemini plus a few other useful utilities including T-NET see The_Gemini_80-Bus_Saga#Installing_T-Net.

Two changes have been made to this BIOS as follows:

  • CP/M has been relocated for use with a 64K system.
  • The floppy disk definition has been changed to support GEMQDDS 80 track 788K drives rather than the 35 track DDDS disks.

File:GM512 64K.80.ZIP

This system image is a 32K CP/M image in GEMDDDS 35 track format that has been patched to work over the G811 serial port rather than the IVC/SVC video card and is useful in cased where the video card is faulty or not present. See The_Gemini_80-Bus_Saga#CP.2FM_Via_the_Serial_Port for details.


Useful Disk Utilities


GemZap Assembler and GemDebug.



DBase 241


Turbo Pascal 3.0 updated for the IVC Video Card (see Configuring_Turbo_Pascal_3.0_for_the_Gemini_IVC_Card).


Wordstar 3 updated for the IVC Video Card (see Patching_Wordstar_3.0_for_the_Gemini_IVC_Card).

File:WS3 IVC.80.ZIP




ROM Images

This is the last RP/M ROM image produced and includes ASC files with the serial default set for 300 and 9600 baud.


Simon 4.1 taken from a Gemini GM925 Multi-Format system.

File:SIMON V4.1

This version 2.2 of RP/M was (supposedly) never released, the version numbers leapt from V2.1 to V2.3 to avoid confusion with version 2.2 of CP/M, this was confirmed in an article written for 80-bus news by RP/M's creator Richard Beal (80-BUS vol. 3 iss. 6 p. 9). However, this image was discovered on a Multi-Board machine in 2019 and attempts to boot in a different way to the normal RP/M. It is presented here for completeness.


The following ROMs were taken from various G812 IVC Video cards.



File:IVC-GEN V1.0

The following ROM was taken from a G832 SVC Video card.


Gemini CP/M Bios

The source code for the Gemini Multiboard Auto Density System (1.4) BIOS is located in the following GIT repository. Whilst the BIOS isversion 1.4, the CP/M version is 2.2.

The repository contains both the original version (1.4) and the version adapted for the GEMQDDDS 788k 80 track disk format (1.4 - QDDS). Each version of the BIOS reports its version as shown below.

   Gemini Multiboard Auto Density System (1.4)   
   64k CP/M vers 2.2   
  Gemini Multiboard Auto Density System (1.4 - QDDS)
  64k CP/M vers 2.2




80-Bus News

Volume 1

Volume 2

Volume 3

Volume 4

Scorpio News

Volume 1

Volume 2

Volume 3


At the moment this is just a list of my Gemini related bookmarks, I will sort these out and add some descriptions soon...