UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Gemini 80-Bus System

john_newcombe · 7th Dec 2019, 2:46 pm

I have some documentation that may shed some light on the GM849 changes.

The previous owner of this machine bought it from new and had an annual support contract for some years. During that time (Oct 1986) the machine was returned for modifications.

I also have an un-dated letter that suggests that one of the updates included a 'new' disk controller, although it does not mention any details. The new controller was apparently changed to allow for many 'non-standard' disk formats to be supported, e.g. 'U' format, unconventional side fields, reverse sides, either physical or logical non-standard sector lengths, logical skewing on both sides of the disk, deleted data marks.

The un-dated letter also suggests that this new controller allowed for 4 external floppy disks and user configurable Winchester partitioning with an alternative OS on track 1 and refers to the previous system as MFB 1. As I also have an MFB 2 software manual I am wondering if the modified GM849 is the 'new' controller mentioned.

7th Dec 2019, 2:46 pm	#275
john_newcombe Hexode Join Date: Apr 2019 Location: Skipton, North Yorkshire, UK. Posts: 252	Re: Gemini 80-Bus System I have some documentation that may shed some light on the GM849 changes. The previous owner of this machine bought it from new and had an annual support contract for some years. During that time (Oct 1986) the machine was returned for modifications. I also have an un-dated letter that suggests that one of the updates included a 'new' disk controller, although it does not mention any details. The new controller was apparently changed to allow for many 'non-standard' disk formats to be supported, e.g. 'U' format, unconventional side fields, reverse sides, either physical or logical non-standard sector lengths, logical skewing on both sides of the disk, deleted data marks. The un-dated letter also suggests that this new controller allowed for 4 external floppy disks and user configurable Winchester partitioning with an alternative OS on track 1 and refers to the previous system as MFB 1. As I also have an MFB 2 software manual I am wondering if the modified GM849 is the 'new' controller mentioned. Last edited by john_newcombe; 7th Dec 2019 at 2:54 pm.