> - Assume this is a blank disk
> - Assume the user has said he wants to use the whole disk for NetBSD (in
> which case any existing MBR doesn't matter much anyway)
> - Assume the disk is larger than the 1024/16/63 limit
> 
> In that case, why can't sysinst just write an MBR with 1024/16/63
> geometry and be done with it?

Because that won't work in general.

In particular, if you did that to my second SCSI disk, the Adaptec BIOS
would refuse to boot it -- any time you try, it cold-boots the machine for
you. I tried making it the official boot device in the BIOS menu -- no luck.

As far as I can tell, the Adaptec BIOS translation is either:

	xxxx/64/32
	xxxx/255/63

with the latter being used when the "> 1 GB translation" feature is enabled.

I generally run with the xxxx/64/32 setting so that each 'cylinder' in DOS
partition managers is exactly one megabyte. Then I just make sure my NetBSD
'a' partition is in the first Gig of the disk. Pretty simple once you get
used to it.

It really looks as if the geometry in the MBR is there so that programs can
avoid querying the BIOS for the geometry information. I don't see any
indication that the BIOS actually pays attention to those MBR numbers.

Todd Whitesel
toddpw @ best.com