Re: Native /// bootstrapping?

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

On Feb 23, 9:10 pm, demp...@actrix.gen.nz (David Empson) wrote:
> Drive-by curiosity makes me ask...
>
> How does that tally with the original layout of ProDOS 5.25" boot disks,
> which have the ProDOS boot loader in block 0 and the SOS boot loader in
> block 1?

The /// seems to be able to consume a boot loader in either block 0 or
block 1.  (A simplifying assumption Jeppson didn't discuss.)  The SOS
Utility Disk will format a disk with the loader in block 0, but early
ProDOS formatters will put ProDOS in block 0 and SOS in block 1.

> Is there some trick the Apple /// is doing to recognise valid code in
> block 0 and if it can't find it, trying block 1 instead, or is part of
> the ProDOS boot block actually a SOS stub loader (at some offset into
> the block) which fetches and executes block 1?

It's probably just in the ROM - to check for something valid before
accepting and executing it.