# PC bootloader (for partitions)

The unit at xcomp/i386/pc/pbr.fs compiles a PBR (partition boot record) which
is the second-stage bootloader after the MBR (master boot record). It is very
similar to [doc/xcomp/i386/pc/mbr.txt] except it 1) must use LBA mode, and 2)
expects DS:SI to point to a 16-byte partition table entry in the relocated MBR.
It copies that to $7d60 and then builds the disk address packet structure for
LBA mode disk operations at $7d70 based on the LBA parts of the partition table
entry.

Note that Dusk booting expects the 32-bit unsigned number at $7d68 to be the
0-based first sector of the FAT filesystem (containing FAT parameters), and the
32-bit unsigned number at $7d6c to be either zero (indicating a whole disk Dusk
deployment) or a nonzero partition size (indicating a partition Dusk
deployment). See [xcomp/i386/pc/glue.fs].
