[Coco] The .DSK format/structure

[Aaron Wolfe]

OS9 (and nitros9) file systems use the RBF format and are relatively easy
to detect by looking for a valid RBF volume header in the first few
sectors.  There are a number of sanity checks that can be done to validate
an RBF filesystem.

DECB filesystems are harder to be sure of, but by looking for reasonable
values in the directory sector and cluster chain you can still be fairly
sure (also, the fact that a disk does not contain an RBF filesystem makes
it likely to contain a DECB filesystem, though there are certainly some
exceptions.)

DriveWire uses a system of checks and votes to determine what filesystem is
present in a .DSK image.  It is not foolproof in theory, but in practice
seems to be accurate with real world situations.

The code can be found here and used or adapted in any way anyone would like:

http://drivewireserver.cvs.sourceforge.net/viewvc/drivewireserver/drivewireserver/java/src/com/groupunix/drivewireserver/dwdisk/filesystem/
 On Aug 22, 2014 10:03 PM, "Salvador Garcia" <ssalvadorgarcia at netscape.net>
wrote:

> Ok, I'm curious. If the DSK is just a raw image of the disk then it
> follows that its "format" is that of the operating system that wrote that
> image. So this begs the next question (at least for me). How would I go
> about knowing the format of the disk? In MS-DOS there was the boot sector
> (for floppies), followed by 2 copies of the FAT and finally the directory
> structure. Is such information available for DECB and OS/9? (Assimng that
> NitrOS9 shares the same disk format with OS/9). Salvador
>
>
>
>
>
>
>
>
> -----Original Message-----
> From: Mark McDougall <msmcdoug at iinet.net.au>
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> Sent: Fri, Aug 22, 2014 6:26 pm
> Subject: Re: [Coco] The .DSK format/structure
>
>
> On 23/08/2014 12:56 AM, Tony Cappellini wrote:
>
> > I want to look at the differences between the Apple2 and coco .DSK
> images.
> > Would someone point me to the following:
>
> Differences - absolutely none!
>
> Both are raw dumps of sector data.
>
> > I want to write a small program that will detect the image type and dump
> > the contents of either disk image.
>
> The DSK files *are* dumps of the disk image.
>
> Regards,
>
> --
> |              Mark McDougall                | "Electrical Engineers do it
> |  <http://members.iinet.net.au/~msmcdoug>   |   with less resistance!"
>
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