🚀 go-pugleaf

Well, at long last we've got a 3.5 inch drive for one of our IBM/PCs.  I've
determined the following..  Using a disk formatted on the IBM, you can
write files on the IBM to be read by the ST, and you can write files on the
ST to be read by the IBM. At least as far as I tried it, you can 'mix and
match'.  That is, you can write some files on the IBM, add some more on the
ST, add some more on the IBM, and so on, and everything works.  (Though
NOTE, keeping Moshe's comments in mind, so far I've only tryed playing
with files on the ROOT of the disk.  Haven't tried folders/subdirectories.

As an experiment, I tried putting some files (on the ST) onto a STANDARD ST
formatted disk (formatted from the desktop menu command).  As rumoured, the
PC could not cope with this disk.  However, our PC guru determined that by
patching 4 bytes in the disk header, the disk could be made to work on the
PC.  These were (all values in HEX):

     offset in boot sector (sector 0)    change
                 00                    from 00 to EB
                 01                     from 00 to 34
                 02                    from 4E to 90
                 36                    from 4E to FA

(Again, note that's 36 HEX.)  The first 3 bytes are a JUMP instruction for
an 8086 family micro.  It is possible that this change might mean you could
not BOOT from this disk on the ST.  Byte 36 is the 'media description byte'
for a 720K (formatted) disk.  A different value is probably required if you
are using a single sided disk (we tried DS).  The Atari can happily read the
patched disk.

Cheers, Paul