Re: IIGS Partitions

["Peter Watson" <paw77@NOhotmailSPAM.com>]

"ground.ecn AppleII Librarian" <apple2pd@garp3.icaen.uiowa.edu> wrote in
message news:9c6njr$9ca$1@server05.icaen.uiowa.edu...
> In article <3ae63d83.286726005@news1.on.sympatico.ca>,
> Jeff Blakeney <CUTjefbla@bconnex.net> wrote:
> >
> >Actually, Mark is correct that the MS-DOS FST only supports floppy
> >disks so it is currently limited to 1440 KB.
> >
> >To access anything larger you have to use Peter Watson's MS-DOS
> >Utilities or MUG!.
>
> Jeff, I agree with your answer as a 'practical' answer, but I do think the
> MS-DOS FST can read larger volumes.  I know that I use 2880K MS_DOS
> volumes with the MS_DOS FST and Kegs emulator and haven't noticed
> problems.  I have also made larger (20Meg) MS_DOS volumes for use with
> Kegs, but I can't recall if I can use the MS_DOS FST or need MUG! to read
> those volume images.  I haven't tried accessing a Zip disk in MS_DOS
> format on a IIGS so I can't comment on 100MB (or 250MB) MS_DOS volumes.
>
> On a IIGS floppy, 1440K is max because I don't think the SuperDrive
> controller will handle 2880K volumes.  Thus, you gave the true 'practical'
> answer :-), but that is a hardware constraint - not a FST constraint.
>
>  --Steve  (apple2pd@ground.ecn.uiowa.edu)

(Disclaimer: I probably actually looked at the code many years ago, but
I don't remember so this is all just supposition. Also, for me it's the
early
hours of the morning and I don't have my source code handy!)

MS-DOS pretty much relies on the boot parameter block to define the
characteristics of a disk. I can vouch that there's very little additional
work to support the various 3.5" and 5.25" disk formats once you've
written the code (properly!) for any one of them.

The real issues are:
1) partition tables
2) a disk large enough to require a 16-bit (or greater) FAT. The MS-DOS

I *know* that the MS-DOS FST can't handle (MS-DOS) partitions, and I'm
fairly certain it can't handle a 16-bit FAT. This means the largest volume
it
should be able to handle will have around 4080 clusters and/or 65536 blocks.
That implies a maximum volume size of 32Mb, although my memory keeps
telling me that volumes over 12Mb are usually formatted with a 16-bit FAT.

The 21Mb Floptical drives may be recognised because they don't use a
partition table, but I can't remember whether they use a 12-bit or 16-bit
FAT.

The MS-DOS Utilities and MUG! went to great lengths to be able to handle
*any* disk (although 32-bit FAT suuport was just too much work to add!)
for reading and writing. Formatting I had to limit to fixed sizes,
unfortunately.

My understanding is that Apple (I think it was Greg Branche) just wanted to
have something to read MS-DOS floppies in the SuperDrive, so that's all it
was written for. (Just to make us all wistful, Greg had a prototype MS-DOS
FST with support for *writing*, but it never made it past the powers-that-be
at Apple. My guess is that they didn't want to put the resources into
testing
that a 'writeable' FST would entail. If a read-only FST doesn't work, no
damage
is done and the user can just find a real PC. But if you mess up writing to
a
disk, users get *very* unhappy...)
--
Peter Watson
-- Write to MSDOS disks on the Apple IIgs?
-- Impossible!  ;-)