Re: Why won't DOS 3.3 work with a ProFile?

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <3qt5ea$bpp@acme.freenet.columbus.oh.us>,
Dave Althoff <dalloff@freenet.columbus.oh.us> wrote:
> 
> I think the truth is that nobody has bothered to write a device driver for
> the ProFile under DOS 3.3.  I mean, the ProFile is a block device as far
> as ProDOS is concerned, but based on what little I know of 3.3 internals,
> there is no reason that DOS 3.3 couldn't be hacked to handle the ProFile.

It wouldn't be easy.  DOS 3.3's maximum volume size is 400K (50 tracks
with 32 sectors per track).  This is why the various programs that
patch DOS 3.3 to work on a 3.5" disk must split it into two 400K
volumes.

To use a ProFILE with DOS 3.3, you would have to arrange some way to
"partition" it into 400k or smaller volumes.

Many DOS 3.3-compatible hard drives do this by usurping the "volume
number" parameter.  On a 5.25" disk, this is very rarely used.  Its
intended function is to ensure that the correct disk is in the drive,
by assigning a unique volume number to the disk at format time.  If no
volume number was specified, the disk defaults to volume 254.  If you
have a volume number set and you try to access a disk with a different
volume number, you get a "volume mismatch" error.

On a hard drive with this patch, the "V" parameter selects the
partition number, and subsequent DOS commands will access the selected
volume.

To do this on a ProFILE would require squirrelling away a reasonable
amount of code inside RWTS, in such a way that it didn't interfere
with 5.25" disk accesses.  This might be tricky (you'd have to disable
the INIT command, at the very least).

Using the volume technique, DOS 3.3 can support up to 253 volumes of
140K each (35420K) or 253 volumes of 400K each (101200K), but managing
it all is a bit of a nightmare.


If you were careful, you could even arrange for DOS 3.3 and ProDOS to
share the same hard drive, by placing the DOS 3.3 portion at the end
of the volume, and leaving the rest for ProDOS.  The DOS 3.3 area
should be marked as used in the bitmap, and appear as a "Pascal area"
file in the ProDOS directory.

It might be possible to extend this further and also support Apple
Pascal on the same volume (only possible with a ProFILE and the Apple
Pascal ProFILE Manager), by setting aside logical Pascal volumes as
DOS 3.3 volumes, and avoiding their use from Pascal.


Why go to all the trouble, though?  DOS 3.3 was not designed to work
with a hard drive, and you have to bend over backwards to get it to
work.  Even then, there will be a fair number of programs that won't
work on a hard drive.

> One problem you might run into, though, is if the programs in question
> access the disk directly rather than going through RWTS.

Or it makes assumptions about the disk organisation, e.g. catalog on
track 17, number of sectors per track, etc.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand