Fred Cisin cisin at
Wed Feb 3 19:47:16 CST 2021

On Wed, 3 Feb 2021, Fred Cisin via cctalk wrote:
. . . 
> Then try cylinder 36.
> If the disk had been written on a 48tpi 35 track drive (SA400/SA390 used on 
> TRS80 and Apple), then cylinder 72 of a 96tpi/cylinder 36 of 48tpi would not 
> have been used.  If cylinder 72 does not read, but 36 gives a valid read that 
> identifies itself as track 18, then it is most likely from a 35 track 48tpi 
> drive, such as SA400.

That second attempt should have read cylinder 54/27, not 36/18
Again, to try to do most of the analysis on the less likely to be in use 

THIRD attempt should be 36/18

Then, if you are feeling bold, cylinder 0
Cylinder 0 may be a different format than other parts of the disk, such 
as the continuation of FM for system tracks of CP/M even after the rest 
of the disk went to MFM.

Watch for what looks like it might be a DIRectory in the low tracks, OR 
for some formats the MIDDLE tracks (17,20, etc) for variants of TRSDOS, 
Microsoft Stand-Alone BASIC, etc.

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