The behavior of fdisk, when used to define an OpenBSD partition on a
i386 PC, is confusing. During the installation of the basic
operating system, if you elect to use the entire disk for OpenBSD, fdisk
starts the OpenBSD partition at sector 63 (typically the
second track of the boot disk). However, if you do not use the entire
disk for the OpenBSD partition, fdisk lets you start the
OpenBSD partition at sector 0.
As i found out after an upgrade, starting the partition at sector 0
causes major problems. I've since reinstalled the software, starting
the OpenBSD partition at sector 63.
The documentation explaining why the OpenBSD partition has to start at
sector 63 is sparse at best.
Why does the OpenBSD partition have to start at sector 63? What is
located in sectors 0 thru 62 that should not be overwritten
by the OpenBSD partition? I know it's something to do with the master
boot record (MBR). Is the entire first track of the disk
reserved for it and it's associated data structures? A bit of detail
would be appreciated and the fdisk(8) man page should mention
the need for the OpenBSD partition to start at sector 63 on this platform.