#321 Raw DD disk image format

[Martin Rosenau]

I'm currently testing a "raw" DD disk image file format for the 1581 (but it could also be used with MFM disks in the 1571).

The file contains the "raw" data, 6250 bytes per track, as it would be read by the "read track" command of the 177x IC.

This file format allows representing non-standard formatting such as 640, 720 or 880 KiB, defective sectors, non-standard sector numbering (as used by Amstrad CPC) and different sector sizes (128,256 or 1024 bytes per physical sector).

My idea is to run some "data transfer" tools that allow reading and writing disks of other systems (such as MS-DOS) on a 1581 drive in VICE.

Would it make sense to support such a file format?

[Ingo Korb]

Ignoring any possible benefits of the format, I think "DD" is a really bad name for it. dd is the name of a Unix tool that can be used among other things to create sector-dump images, so there is a large chance that people will confuse such images and your format.

As for the format itself, wouldn't it be better to go even lower and store pulse stream timing relative to the index hole for more generality? I'm not familiar with the 177x FDCs, but if there are any copy protection mechanisms that rely on information being read differently in every attempt a single "read track" dump wouldn't be sufficient to represent them, but a pulse stream could.

[Martin Rosenau]

"DD" was not intended to be the name of the format; I wanted to say that the format describes a double density floppy disk, which was labelled "DD" in the 1980s.

Storing the single pulses would allow to use such a format for RLL disks instead of MFM disks so 1541 disks could also be described by this format. On the other hand I saw that VICE (I had a look at the 3.2 sources) internally already uses the file format I suggested to store. The data sheets of the WD177x and the uPD7xx65 disk controllers name that format "raw" or "low level".

[gpz]

my first question would be: is there any software that requires this to work?

but sure, such format would be needed (i'd opt for some already existing format). properly supporting 1571 would be even more fun, since we can mix gcr and mfm on a disk :)

[Martin Rosenau]

I started the work on this format because I wanted to test data transfer tools. One example would be "Big Blue Reader", which is a tool that can read, write and format MS-DOS disks on a 1581.

Especially when a sector size of 256 or 1024 bytes is used (which would be the case for Acorn disks), such tools won't work with any of the present disk formats.

[Martin Rosenau]

(Deleted; posted comment as "Reply" instead)