Re: ADTgs issues

[pausch@saaf.se (Paul Schlyter)]

In article <4537767d$0$30328$9b4e6d93@newsspool1.arcor-online.net>,
Linards Ticmanis  <ticmanis@gmx.de> wrote:

> Alex Freed wrote:
> 
>>> Michael, I always wondered if DOS3.3 and ProDOS disks were essentially
>>> formatted in the same way.
>> 
>> Yes at some level: the physical format of the sectors is mostly the same
>> (apart from interleaving). However
>> ProDOS treats pairs of sectors as 512 byte blocks.
> 
> No, the interleaving is the same (namely none) on the physical sector
> level. The sector numbers in the sector headers on the disk increase in
> steps of one on every track.
> 
> The two systems both renumber the physical sectors into logical sectors
> in two different ways, and ProDOS additionally treats pairs of sectors
> as logical blocks, but all that has nothing to do with the low-level format.
> 
> Only DOS 3.1 / 3.2, i.e. 13-sector disks, use physical sector level
> interleaving; on the other hand, they don't do any logical renumbering
> of sectors.

Actually, 13-sector Apple CP/M used physical interleaving too.... yes,
there was a 13-sector version of SoftCard CP/M for a short time after
its initial release (I still have a 13 sector SoftCard CP/M master
disk).  It used an interleaving suitable for CP/M (every 3rd sector in
ascending order, rather than every 2nd sector in descending order as
used by DOS 3.1/3.2).

On top of that, Apple CP/M had a logical renumbering of sectors, but in
the other direction: while ProDOS and Apple Pascal treated pairs of sectors
as 512-byte logical sectors, Apple CP/M did split each physical sector into
two logical sectors of 128 bytes each, since that was the norm in the CP/M
world.

> The only difference in 5.25 inch low-level format between DOS 3.3 and
> ProDOS disks is that DOS 3.3 disks are usually formatted with a volume
> number of 254 (but this is changeable), while ProDOS uses volume number
> 1 (not easily changeable).

Apple CP/M always wrote volume number 0 onto the disks when formatting
them, and ignored the volume number while accessing the disks.

-- 
----------------------------------------------------------------
Paul Schlyter,  Grev Turegatan 40,  SE-114 38 Stockholm,  SWEDEN
e-mail:  pausch at stockholm dot bostream dot se
WWW:     http://stjarnhimlen.se/