Re: SOS file system information

[schmidtd <schmidtd@my-deja.com>]

On Mar 23, 2:06 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> Linards Ticmanis wrote:
> > On 03/22/2011 03:21 PM, schmidtd wrote:
>
> >>On boot, ROM loads block 0 into $A000 (the upper S-bank, always
> >>present) and control is passed to it.  It's straight code; there's no
> >>header, counters or signatures.  There's something else that happens
> >>to enable dual-booting - ProDOS boot can be in block 0, while SOS boot
> >>is in block 1.  I don't recall what that is.
>
> > AFAIR, it has to do with the fact that Apple II booting passes control
> > to the second byte of block 0 (loaded at $0800), while Apple III goes to
> > the first byte. So with some tricky code you can have it do different
> > things.
>
> Interesting.
>
> But I thought that Block 1 was the SOS boot block...

It is, with the early ProDOS formatted disks.  If SOS formats it, it's
in block zero.  If ProDOS formats it, ProDOS is in block zero, SOS is
in block one.  And as Linards says, the difference is the length byte
that ProDOS puts at the beginning, where SOS doesn't.