Date   : Tue, 15 Jun 1999 01:00:55 +0100 (BST)
From   : Mr M F Scholes <mavhc@...>
Subject: Re: BBC software to grab DFS disc images

On Mon, 14 Jun 1999, Steven Flintham wrote:

> On Mon, Jun 14, 1999 at 10:58:54AM +0200, Robert Schmidt wrote:
> > With your suggested scheme, such space saving is not too easy:
> [...]
> > - you'd need to extend the format to tell any reading tool how many
> >   tracks there are (if you'd like to support 40T).
> 
> I'm pretty sure this information (more precisely, the number of
> sectors) is embedded in the first two sectors of track 0 on each side.
> If this is correct, I think this limitation could be worked round
> without extra data, although it would be slightly tedious having to
> work out the size of the first side before accessing the second side
> (if there is one).
Yes Track 0, Sector 1 Bytes 06 and 07, the high nibble of btye 06 is the
opt, the low nibble*256+byte 07 = number of secotrs on one side a the
disc, usually &320 for 80 track and &190 for 40 track.
> 
> This assumes standard DFS format, but I'm not sure that's a problem in
> itself as only protected discs would be different (AFAIK) and I doubt
> any format along these lines will work in this case.
Double density discs will have different numbers there, eg a 16 sector per
track 80 track disc would have &500

Me, spend days editing discs with a sector editor? Only when Solidisk
decided to write over the catalouge!

Mark Scholes