Re: IIGS - Mac - ProDos

["bieling@terra.es" <bieling@terra.es>]

On Feb 27, 8:58 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> Unfortunately, that isn't going to work.
>
> There is no way that the Mac can know that the non-standard MicroDrive
> partition table is written to the first few blocks of the device.
>
> Unless you write a custom driver, a Mac will never be able to mount
> the device as 8 ProDOS volumes.
>
> The Mac *requires* that partitioned volumes have a *Mac standard*
> partition table (in its own partition!) written to the device, and
> such a table contains a Mac driver for the device!
>

More or less. The Mac will start by looking for the signature bytes in
a block device. If it's signed as Mac-formatted, then yes, it will
look further for an Apple Partition Type partition table, and then, if
there's not a correct partition table, will post a message saying that
the volume is "not formatted" or "could not be read" or something. If
the partition table is found and is correct, it tells the mac where do
the patitions begin and end. These partitions can hold a driver, or
nothing at all, or any other filesystem that the Mac knows about, for
example one HFS patition, one HFS+ partition, one FAT partition, one
ProDOS partition, one UFS partiton can all live at the same time in
the same device and all of them will mount and be readlily available
in the desktop at the same time.

But, if that (Apple) signature is not found, it will try to guess what
kind of format the device has, be it MSDOS-like, or UFS, or a ProDOS
volume, etc.

You can plug for example a ProDOS or an MSDOS formatted drive that has
never seen a Mac and the Mac will mount it perfectly, even though it
lacks the Mac signature and Apple partition table type, because ProDos
and MDOS volumes have their own "signatures" too that the MacOS will
recognize and it will therefore choose and use the proper filesystem
extension to deal with the device.

If what the Mac sees in the first block of the device matches the
pattern that the Mac looks for when searching for a ProDOS volume, it
will try to mount that device as a ProDOS volume.

As you can see, it is not mandatory to find an Apple Partition.

The problem in this case is that the signature in the first block is
not being properly recognized for some reason as belonging to a ProDOS
formatted volume. The reason may be that the ProDos volume itself is
non-standard in some way, or that the ProDOS volume itself is shifted
a block for some reason, most likely the MicroDrive's fault. My other
best guess is that the Mac is not expecting to find a ProDOS volume in
such a huge device, and is therefore not even looking for a ProDOS
signature in it.

OTOH, yes, you're right that it will be very dificult to get any
ProDOS partition mounted beyond the first one. But the first one at
least should get mounted, I believe.

Jorge