Re: trying to get an Apple II GS going for fun...

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

Supertimer <supertimer@aol.com> wrote:

> wizard@direct.ca (Astro) wrote:
> 
> >You load ProDOS by using a boot disk? You would use a ProDOS boot disk
> >as opposed to, in my case [given my hardware limitations] the System
> >5.0.4 system disk? If this is yes, is the ProDOS boot disk itself a
> >disk image?

[Various snippages from SuperTimer's excellent description of FSTs]

> Think of GS/OS as having an additional layer.
> 
> Graphically, MacOS and Win 95 are like this:
> 
> Program -> MacOS (hardwired HFS or HFS+) -> disk
> 
> Program -> Win95 (hardwired FAT or FAT32) -> disk
> 
> But GS/OS is like the following, just like OS/2 and Linux:
> 
> Program -> GS/OS -> FST -> disk

I thought I should point out that WinNT works like this as well.

> Under GS/OS, you can drop a new FST module file into
> the FST folder and access a new kind of file system.  To
> the program, it'll be the same thing because it does not
> know or care which file system it is.

Just to flesh this out somewhat:

ProDOS and HFS are supported fully for both read and write, and for
native storage of GS/OS applications and data files.  The only
limitations of HFS support are an inability to boot the IIgs from an HFS
disk, and lack of IIgs-based tools for handling disk repair and
optimization.

There is also the AppleShare FST, which supports full read/write (and
boot) access to an AppleShare server, or a Mac running File Sharing (but
this doesn't support booting the IIgs over the network).

System 6.0.1 also has FSTs which implement read-only support for several
file systems, allowing files to be imported to the IIgs:

DOS 3.3 (the older Apple II operating system)

Apple II Pascal

MS-DOS (FAT) - generally requires special disk hardware due to
formatting incompatibilties

High Sierra and ISO9660 (CD-ROMs)


The DOS 3.3, Pascal and MS-DOS FSTs are limited to supporting floppy
disks.  I suspect HighSierra/ISO is limited to supporting CD-ROMs
(probably a moot point, as it is almost never used anywhere else).

The only major omissions are a CP/M FST (for Apple II CP/M 5.25" disks)
and limited features of the MS-DOS FST: ideally, it should have write
access, support for hard drives, and (now) long(ish) filename and FAT32
support.

> The same thing can be done in OS/2 and Linux.  But under MacOS, for
> example, you'd need to basically patch the OS, which is what PC Exchange
> does.

The Mac does have limited support for installable file systems, which is
used for CD-ROM support, for example.  (It might be limited to read-only
access.)  PC Exchange has to go somewhat further than this, in
particular to deal with retaining Mac-specific information like resource
forks and directory information on an MS-DOS or ProDOS disk.

> So why does removing the ProDOS FST prevent GS/OS
> from accessing ProDOS disks?  Because GS/OS would
> no longer know how to access a ProDOS disk.  Remember,
> the FST sits between GS/OS and the disk.  The ProDOS
> file system is not hardwired into GS/OS.

It is worth noting that the local boot mechanism is tied to ProDOS, for
compatibility with ProDOS-8.  The boot block contains the same code for
ProDOS-8 and GS/OS: it looks for a file called PRODOS in the root
directory, loads it and jumps to it.

In the case of ProDOS-8, this file is the actual ProDOS-8 operating
system.

In the case of GS/OS, this file is the first stage OS loader, which
deals with getting the main parts of the operating system into memory
(particularly Start.GS.OS).  Apart from the boot sector and ProDOS FST,
this is the only component of GS/OS which is hard-wired to the ProDOS
file system.  (In effect, the PRODOS file has a read-only implementation
of the ProDOS file system, which only supports reading files from the
System folder on the boot volume.)

Start.GS.OS uses code provided by the generic OS loader to deal with the
file system and load the corresponding FST, which then takes over
handling the file system.

This system was designed to be able to support booting on other file
systems in future, but Apple never went anywhere with it.

The AppleShare boot mechanism is somewhat different, but ends up going
through the same general mechanism.

HFS can't be booted on the IIgs anyway, given the existing firmware,
because the organisation of HFS block 0 conflicts with the boot sector
definition for the Apple II.  In theory, Apple could have added HFS boot
support in a future revision of the IIgs ROM firmware (or the SuperDrive
card and SCSI card firmware), by doing a pre-boot check for an HFS disk
and using a ROM-based OS loader in the same manner as the existing
PRODOS file.

The same applies to an MS-DOS (FAT) disk, to a lesser extent: a floppy
disk could be set up to boot either a PC or an Apple II, but not both
(without firmware support in the Apple II), since the boot code lives in
the same place for both platforms.  Booting from an MS-DOS hard disk
would require support for the PC's partitioning scheme in the interface
card firmware, so a special method could be used to avoid interference
with the PC boot process.

> If you boot over an AppleShare server over a LocalTalk
> network, I think you can even remove the ProDOS FST
> completely, but then you can no longer read ProDOS
> disks on your local drive.

Correct.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand