🚀 go-pugleaf

: P.S. Does anyone know what the "NON-IBM" bit actually does in the attributes
: of a block device?  does anything use it?

The DEC Rainbow 100 uses it.  The Rainbow's disks have their own "boot sector"
format because the Rainbow gets booted from a Z80 and the code that is on
the boot block is for a Z80.  Also, the Rainbow was mostly designed when they
decided to add MS-DOS support for it.  Also, the Rainbow has some odd formatted
disks.  1 side 80 tracks 10 sectors per track.  That's not the reason that
it has the NON-IBM flag.  Heck, two FAT ID bytes are reserved for use by
Rainbow disks (FA and FB).

From reading my documentation on writing device drivers, the NON-IBM bit
means that the driver will pass you one sector's worth of buffer space when
DOS want you to build the BPB to pass back to it.  That's about the only
difference that I can see.

In DOS 3.10 it is very possible to write a device driver that tells dos
what is on the boot block and have it mostly believed (2 FATs seem to be
etched in code somewhere, however).  I've done it so I can use 3.5" disks
(more or less) in my Rainbow.  Too bad they don't format the same as on a
PC at the moment :-(.

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