JdBP> The problem with the INT 13h Extensions is threefold:  Not all
 JdBP> BIOSes implement these extensions, not all BIOSes implement these
 JdBP> extensions correctly, and not all operating system vendors have
 JdBP> caught up.  

The fact that not all BIOSes implement these extensions correctly shows up
when one tries to use these extensions as standard for everything, by the way. 
 The BIOS on my machine here has a bug in its INT 13h extensions
implementation, for example.  It works just fine for BIOS units 80 and above,
but goes wrong when used for BIOS units 00 to 7F (at least when those units
are ATAPI devices).  It reads more sectors than specified by the sector count
passed to it, overwriting memory that it should not as a result.

Of course, one way of solving this is to have a special boot sector used only
for floppy discs that uses the standard INT 13h API.  Windows NT is one
operating system that can quite easily get away with this scheme, for
instance, since because with Windows NT one has to jump through several hoops
to make a bootable floppy disc *anyway*, adding one more whereby one has to
specify a special floppy boot sector is not, comparatively, that much more of
a hardship.

It is much more difficult to get away with this scheme on OS/2 should one want 
to, since it is comparatively very easy to create customised bootable OS/2
floppy discs.

 ¯ JdeBP ®

--- FleetStreet 1.22 NR
143/1