Date : Wed, 08 Apr 2009 17:00:43 +0100
From : jgh@... (Jonathan Graham Harston)
Subject: Writing BBC Disc Images on Linux
Alex Taylor wrote:
> I've often wondered if there's any technical reason why you can't just
> write an identical copy of each track twice when writing a 40-track
> disk with an 80-track drive, rather than double-stepping. This might
'cos every second track will be half-way between the other tracks.
You end up with:
-96-dpi-track-0-------- -48-dpi-track-0---
-96-dpi-track-1--------
-96-dpi-track-2-------- -48-dpi-track-1---
-96-dpi-track-3--------
If you write the same track twice in a 96-dpi drive, then the
48-dpi drive will pick up data from the previous track:
-96-dpi-track-0-------- -48-dpi-track-0----
-96-dpi-track-1-------- -copy-of-track-0---
-96-dpi-track-2-------- -48-dpi-track-1----
-96-dpi-track-3-------- -copy-of-track-1---
When the 48-dpi drive positions its head over where it thinks track
1 should be it will pick up the 48-dpi-track-1 with overlap from
the adjacent copy-of-track-0 and copy-of-track-1.
--
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