from David Laight:

> RTFM....
> The mbr (master boot record) in sector 0 defines 4 'partitions'.
> Each has a byte that tell the system what sort of encoding (typically
> a filesystem) is in that partition.
> Most systems and OS will only boot one of these partition (by reading
> then executing its first sector)

> The 'extended' partition is a method of splitting one of the partitions
> into smaller pieces.  DOS understands how the splitting works, Linux
> uses this for its separate filesystems, swap etc.

> NetBSD doesn't believe in anyone elses method of allocating space
> on the disk.  You need a partition in order to boot something,
> netbsd uses the second sector of the partition to describe the layout
> of the entire disk.  Getting Linux to find the bits of a netbsd
> system is probably impossible!

> IMHO netbsd ought to have devices for a reasonable number of
> partitions (following the extended ptn list) that do not use
> the info from the netbsd disklabel.

I think FreeBSD and OpenBSD are similar to NetBSD in the way they access the
hard disk with disklabel rather than primary and logical partitions.  So it
can be tricky to access a secondary non-BSD hard disk which would naturally
not have a BSD disklabel.  I don't think one would want to write a BSD
disklabel on a non-BSD disk, it would likely interfere with something.

Possibly a Linux subpartition could be booted from a NetBSD boot prompt with
something like boot wd0i:vmlinuz , though I am not planning to experiment in
that regard, and I don't know if Linux could recognize a BSD disklabel if the
BSD slice didn't have an entry in the MBR.