Date   : Mon, 14 Jun 1999 10:58:54 +0200
From   : "Robert Schmidt" <robert@...>
Subject: Re: BBC software to grab DFS disc images

Jonathan Graham Harston wrote:
> > The double sided format uses interleaved tracks:
> >  track 0,head 0, sector 0,
> >     .
> >  track 0,head 0, sector 9,
> >  track 0,head 1, sector 0,
> >     .
> >  track 0,head 1, sector 9,
> >  track 1,head 0, sector 0,
> >     etc
> 
> Horrible, horrible, horrible!

I think the idea behind this is to conserve disk space.  BeebEm
supports SSD/DSD images that have been "cut short" - i.e. the file ends
after the last sector with actual data in it.

This also caters nicely for 40/80 track disks - i.e. the number of
tracks is easily determined from the size of the file.

With your suggested scheme, such space saving is not too easy:

- a DSD image will be at least the size of one 80T side, even if only
  the flip side has data.
- you'd need to extend the format to tell any reading tool how many
  tracks there are (if you'd like to support 40T).
 
Though I agree a cleaner format could be desirable.

--
Robert Schmidt <robert@...           > Software Engineer
Technoguide AS: http://www.technoguide.no
Tel: +47 22510463  Fax: +47 22734749
Private: http://www.nvg.unit.no/~rsc
Tel: +47 22606076 

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