Excerpts from netbsd: 21-Jun-97 NetBSD and FreeBSD co-existing Duncan
McEwan@mcs.VUW.AC (1559)

> The FreeBSD partition was in the 2nd half of the disk, and I was trying to
> install NetBSD (1.2G) in the first half.  I also had the os-bs boot
> selector installed in sector 0 of the disk.  My feeling is that installing
> NetBSD is clobbering the FreeBSD bootblocks, or something like that.

NetBSD will overwrite the MBR (and thus os-bs, if present)
if it installed at the beginning of the disk, with partition offset 0.

> Do I have to leave the first track empty?

Yes.

> I thought the first 16
> sectors or so of the root partition were left unused to accomodate the
> secondary bootstrap.

The NetBSD bootstrap uses nearly all of this space (first 15 sectors) for its
own purposes. Bootselectors have to be at different places.

> I noticed that the boot block stuff changed in NetBSD recently.

As far as the use of the first sectors is concerned, there is no difference.

> Are there still primary and secondary boot blocks?

The first steps of startup are unchanged. The installation of the
boot blocks is now done by "installboot", there is no special
handling by "disklabel" anymore.
To be more precise, there are also tertiary boot blocks, which
are located in the file system ("/boot").

best regards
Matthias