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keirf / greaseweazle

Tools for accessing a floppy drive at the raw flux level
The Unlicense
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Add support for BBC DDFS disks/drives #427

Closed LinuxJedi closed 6 months ago

LinuxJedi commented 7 months ago

BBC Micros had the possibility for 80T disks that were FM formatted. The drives typically have a 40/80T switch for this. Typically this would be called DDFS by most manufacturers, although Acorn's 1770 DFS falls into this category.

This commit adds a profile to read disks when hooked up to a BBC Micro disk drive in 80T mode.

Note that there is no DS option as interleaved DS was not really a thing on BBC Micros, sides were given separate drive numbers.

drdpj commented 6 months ago

DDFS was a double density DFS, deployed by Watford (and others) with their 1770 disk interface - it's an MFM format, and could be 40 or 80 track, single or double sided (not interleaved). 80 track FM was simply 80 track DFS format (again, single or double sided not interleaved). Check here for more detail: https://stardot.org.uk/forums/viewtopic.php?p=390348#p390348

On Fri, 31 May 2024 at 09:16, Keir Fraser @.***> wrote:

Merged #427 https://github.com/keirf/greaseweazle/pull/427 into master.

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LinuxJedi commented 6 months ago

DDFS was a double density DFS, deployed by Watford (and others) with their 1770 disk interface - it's an MFM format, and could be 40 or 80 track, single or double sided (not interleaved). 80 track FM was simply 80 track DFS format (again, single or double sided not interleaved). Check here for more detail: https://stardot.org.uk/forums/viewtopic.php?p=390348#p390348

DDFS had multiple meanings depending on vendor. Watford was not the only vendor who used the name "DDFS".

drdpj commented 6 months ago

80 track drives could be used with any DFS, they were always referred to as 80 or 40 track. We've been archiving beeb disks for years, SSD represents a 40 or 80 track single sided FM image (100/200kb) and DSD a double sided image at 40 or 80 tracks - these have always been interleaved sector images although as you rightly say, that's not true to how DFS treats the disks. It is, however, how they've been archived since time immemorial, probably down to how they were originally captured on PC drives. DDFS has always referred to double density - MFM as opposed to FM. Solidisk and Watford produced DDFSs, and probably others. Lots of discussion scattered through stardot over the years, but I promise that DDFS has never been used in the mainstream to differentiate between 40 or 80 track DFS formatted disks (FM, 256byte sectors, 10 sectors/track). It will cause confusion if it is.

On Fri, 31 May 2024 at 20:09, Andrew Hutchings @.***> wrote:

DDFS was a double density DFS, deployed by Watford (and others) with their 1770 disk interface - it's an MFM format, and could be 40 or 80 track, single or double sided (not interleaved). 80 track FM was simply 80 track DFS format (again, single or double sided not interleaved). Check here for more detail: https://stardot.org.uk/forums/viewtopic.php?p=390348#p390348

DDFS had multiple meanings depending on vendor. Watford was not the only vendor who used the name "DDFS".

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