Re: ProDOS Kernel Rewritten

[mjmahon@aol.com (Michael J. Mahon)]

Bryan Parkoff wrote:

>    I am working on ProDOS Kernel that will support hard drive up to 4GB.  I
>understand that some IDE controller card such as Turbo IDE controller card
>(from //SHH Systeme) can only support up to 2GB.  I will allow ProDOS Kernel
>to use 2GB.  I don't know SCSI controller card since I don't carry it with
>me for Apple IIgs.
>    If I get SCSI controller card in my own, I will be able to write device
>driver of ProDOS Kernel that will support 100MB and 250MB Zip Drive.  It may
>be 750MB Zip Drive unless USB controller card will be built for Apple //e &
>IIgs.
>    If SCSI hard drive supports maximum of 4GB, it will be wonderful for me
>to rewrite ProDOS Kernel to handle 4GB.  I do not worry that current ProDOS
>still use 16 bit that handle only 32MB (from block $0000 to block $FFFF).
>New ProDOS Kernel will use 32 bit that handle 4GB (from block $00000000 to
>block $FFFFFFFF).
>    This allows new ProDOS Kernel to be compatible to all original ProDOS
>Kernel that handles 32MB.  I suspect that new ProDOS Kernel might be
>incompatible to GS/OS v6.0.1 unless new FST will be written.  I try to allow
>some GS/OS System files be modified to support 4GB instead of using ProDOS
>FST.  For example, the hard drive will be formatted 2GB before GS/OS v6.0.1
>will be installed.  It gives an ability to be very flexible to overcome the
>limitation of 32MB.
>    I don't know the maximum capacity that HFS (Macintosh Format) handles
>perhap 2GB or 4GB.  Macintosh Utilities will be rewritten to support ProDOS
>4GB for transferring files.  I don't know if Mac OS X still use HFS since I
>understand that it uses Unix format.
>    Please comment your ideas suggesting to handle 4GB of ProDOS format
>while I am working on my project to rewrite ProDOS Kernel.  Thanks a lot...

Bryan,  it is not necessary for a disk to be addressed below the block level,
which for ProDOS is 512 bytes.  Simply adding another high-order disk
address byte will get you 256x32MB or 8GB addressable capacity.

But there are complications.  Compatibility would certainly not extend to
utility programs that require knowledge of the file system data structures
on disk, since they would have to change to accommodate the 3-byte
disk addresses.  As a result, you would need to write new utilities for
disk diagnosis, repair, optimization, and file examination.  You may
find that Macintosh utilities are not the best fit for this purpose.  (But
it would be nice to have an HFS test/fix/optimize utility for the IIgs.  ;-)

Of course, all the ProDOS routines that manipulate file system data
structures would have to be adapted to the new address size and 
24-bit arithmetic.

It isn't that it can't be done--it's a question of usefulness.  As others
have pointed out, a few 32MB ProDOS partitions seem to do the job.

-michael

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