Re: firmware for the PseudoDisk

[Andy McFadden <fadden@fadden.com>]

Michael J. Mahon <mjmahon@aol.com> wrote:
>> What is the partitioning scheme for multiple ProDOS partitions?
>> I *think*  CiderPress can only access a single ProDOS volume on
>> a physical device. And Windows only maps one partition to a logical
>> device.
> 
> There are actually several different methods, depending on the
> controller card.
> 
> Apple's SCSI cards implement a Mac-style partition table.
> 
> CFFA implements "hard" partitions set by the controller, with
> no partitioning table.
> 
> Other IDE cards implement a partition table on disk, but I
> don't know what standard, if any, was used.

The RamFAST SCSI card also uses the Mac-style table.  It's also found
on many Apple CD-ROMs.  (Some are just plain HFS.)

The MicroDrive and FocusDrive have custom formats that allow 30-ish
partitions.

Windows maps one physical partition and multiple logical partitions to
drive letters.  The Windows partition map has space for 4 physical partitions,
only one of which is designated "active"; after that it's chaining "extended"
and "logical" partitions around.

The Mac version is the most generally elegant, but the MicroDrive/FocusDrive
formats are more compact and are better suited for the specific application.

CiderPress will access every partition that can be found.  Not always in
the most aesthetically pleasing manner, but it works. :-)

> This approach essentially replaces Apple partitions with
> FAT files, so only a single FAT partition is needed, with a
> file for each Apple "partition".  Of course, the FAT files
> may not remain physically contiguous, so multiple levels of
> block mapping are required (Apple to FAT and FAT to physical).

Presumably FAT32 would be employed for the larger volumes?

Motivated individuals could use a defrag utility, and the code could
fast-path to direct block read routines when files are contiguous, so
whatever gains are to be achieved by side-stepping the filesystem are not
necessarily lost.

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