Re: File format of .dsk???

[Rubywand <rubywand@swbell.net>]

Theusch writes ...
> 
> I would like any and all information pertaining to the file format of .dsk
> image files.  Specifically, I want to know how to tell where files start and
> end, so I might make a program to add and extract files to/from .dsk files.
> 
 ....

     Here is some additional info ...

     Suppose you look at a standard 5.25" .dsk file on a PC using a Hex editor
(like Hex Workshop).  Each 256-byte block of memory displayed corresponds to the
data contained in a Sector of a 16-sector Apple II diskette. Each 4096-byte block
corresponds to the data in a Track.

     A .dsk disk image file is supposed to use DOS 3.3 sector ordering. What this
means is that the 256-blocks of data will be arranged in sequence corresponding to
sectors DOS 3.3 would call $00-$0F (0-15).  For example, bytes at locations $00000
through $000FF would be the contents of Sector $00 on Track $00. Bytes at locations
$00100 through $001FF would be the contents of Sector $01 on Track $00. The
contents of the last sector on Track $00 would be found (in the hex editor) at byte
locations $00F00 through $00FFF.

     If the disk image is of a DOS 3.3 diskette, you can look at the DOS 3.3 VTOC
for the disk image starting at byte location $11000-- the beginning of Track $11
(17). The first Catalog sector would be displayed at locations $11F00-$11FFF (Track
$11, Sector $0F).  DOS 3.3 Catalog sectors work downward in Track $11; so, the next
Catalog sector starts at location $11E00.

     So, working with DOS 3.3 disk images in DOS 3.3 order is pretty easy. For
ProDOS disk images in DOS 3.3 order, you have to use a table to locate both halves
of a particular 512-byte block.



Rubywand