Apple ][ (clone) disk booting

Tony Duell ard at p850ug1.demon.co.uk
Tue Oct 2 13:34:25 CDT 2007


> Hmm, I don't see the heads move (other than stepping to the outside track at 
> power-on if I've manually moved them) - no luck with PR#6 either (same 
> behaviour; starts the spindle motor, then briefly rattles the heads against 
> the end - outer - stop before just sitting there with the motor turning).

Couild this be a 13 sector .vs. 16 sector issue? 

IIRC, the early Apple disk drives used a 13 sector format. Apple worked 
out a modification (basically allowing some bit patterns that were 
illegal before) to pack 16 sectors on to each track. The modifications to 
a real Apple cotnroller were 2 new PROMs, one was the state machine logic 
(the modified state machine could physiaclly read both 13 and 16 sector 
disks), the other was the bootstrap firmware, and IIRC the new firmware 
would only boot 16 sector disks. Of course an unmodified controller could 
only boot (heck, could only read) 13 sector disks.

> (The DOS disk I have is 3.2 incidentally... the wikipedia article on the A2 
> suggests there was a tweak available for genuine Disk ][ interface cards 
> post-3.2 to allow more sectors per track; I presume that  such 'tweaked' cards 
> will still boot 3.2 and earlier media though? I've got no idea which 'type' of 
>   interface this clone copies)

Aha... IIRC, 3.2 is 13 sector, 3.3 is 16 sector. If your clone is 
expecting 16 sector disks, it will not boot 3.2 AFAIK.

-tony



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