> The geometry you specify to pfdisk needs to match what the BIOS gives
> to the first-stage boot program, otherwise the boot program will get
> the wrong sectors when trying to load the second-stage boot program.

One more data point on this.  Not all BIOS actually write this
geometry on the disk.  This bit me when I added NetBSD-1.0 to an
already DOS disk.

pfdisk gave a reasonable geometry, I added the NetBSD partition, and
proceeded with the install.  O and behold, I got the warning about
existing DOS partition table..I was dump and said yes, overwrite it.

The problem is that the label on the disk had horsepucky values for the
BIOS geometry, the AHA-1542CF BIOS (or maybe the SCSI drivers
loaded later), gave it's standard translation, but didn't actually
write those values to the disk.

So, two safety tips for sharing a disk with DOS and NetBSD:

1.) Run pfdisk (or NetBSD FDISK) and rewrite the BIOS geometry, even
	if it looks right.  You make sure they're on the disk that way.
2.) If you get the warning about the DOS partition table existing, STOP.
	If you've done things correctly, you won't get the warning.
--
Mark