Re: Disks that boot on 13 and 16 sector ROMs?

["josephoswaldgg@hotmail.com" <josephoswald@gmail.com>]

Paul Schlyter wrote:

...
>
> The 13-sector format "Sector 0" is special: it contains the equivalent
> of the 16-sector boot PROM, bot relocated to address $300 (where the
> 13-sector boot PROM loads sector 0).
>
> Booting such a disk with a 13-sector boot PROM works like this:
>
> 1. The 13-sector boot PROM loads the special 13-sector Sector 0 at
> address $300 and then executes the code there.
>
> 2. The code at $300 does the equivalent of the code in a 16-sector
> boot PROM (except recalibrating the disk drive - that has already
> been done by the 13-sector boot PROM and need not be done a second
> time): read in the normal 16-sector Sector 0 at address $800 and
> execute the code there.

Maybe I'm missing something simple, but how can a 13-sector controller
read the 16-sector disk contents?

Seems like it would have to be the other way around: 16-sector
controller reads one sector (or so) in 16-sector format, enough to load
a 13-sector RWTS routine for the completion of the boot.