Date   : Thu, 09 Apr 2009 11:05:08 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Writing BBC Disc Images on Linux

"Mark Haysman" wrote:
> > DSD is a binary dump of the contents of an interleaved disk image.
> > It does track 0 sector 0..9, track 1 sector 0..9, track 0 sector
> > 0..9, etc.
> Can you clairfy that, or is that a typo? I was to understand that .DSD is:
> Side 0 - Track 0 - Sector 0..9
> Side 2 - Track 0 - Sector 0..9
> Side 0 - Track 1 - Sector 0..9
> Side 2 - Track 1 - Sector 0..9
> Side 0 - Track 2 ......etc
> 
> Or is that not right?
 
Disks have two sides, either side 0 and 1 or side 1 and 2 depending
on how you want to count them. Computers tend to count from 0, so
disk sides are 0 and 1, selected with bit 2 of the BBC B+ drive
control register or bit 4 of the Master control register or bit 7
of the 8271 control register.
 
An interleaved disk image goes:
 
Side 0, Track 0, all sectors
Side 1, Track 0, all sectors
Side 0, Track 1, all sectors
Side 1, Track 1, all sectors
Side 0, Track 2, all sectors
Side 1, Track 2, all sectors
Side 0, Track 3, all sectors
Side 1, Track 3, all sectors
Side 0, Track 4, all sectors
Side 1, Track 4, all sectors
Side 0, Track 5, all sectors
Side 1, Track 5, all sectors
...etc...
until you run out of disk.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
RISC OS Internationalisation - http://mdfs.net/Software/RISCOS