Date   : Wed, 16 May 2012 09:35:17 +0100
From   : afra@... (Phill Harvey-Smith)
Subject: Torch discs.

On 16/05/2012 08:53, Jim Hearne wrote:
> It happily reads the disks when set to 40 or 80 tracks, the drive has a
> switch for 40 or 80 track (not labelled) but i think it's in the 80 track
> position or when i tried to read 80 tracks it would hit the endstop on the
> drive.
> How can i be sure if they are 40 or 80 track discs ?
> Would a 40 track disc read as 80 tracks have duplicated data for every other
> track or would it come up with read errors ?

Grab yourself a copy of Sydex's Anadisk, the old DOS version, such as :
http://sta.c64.org/dosprg/anad207.zip

Anadisk can analize the disk and will tell you if there is data on all 
the tracks, generally a 40 track disk in an 80 track drive would come 
read as good tracks interleaved with unreadable or unformatted tracks.

Something like :

Track 0
bad
track 1
bad
track 2
bad

etc

The one exception to this however would be if the disk was initially 
formatted as 80 track and then re-formatted as 40. However in this case 
the track numbers in the sector headers would be out of sequence so 
you'd get :

Track 0 <40
Track 1 <80
Track 1 <40
Track 3 <80
Track 2 <40
Track 5 <80

etc...

Cheers.

Phill.