Статья обновлена и перенесена в NetBSD wiki: http://wiki.netbsd.se/How_NetBSD_boots_on_x86, здесь старый вариант.

1. MBR is read and validated (checked for 0xaa55 at the end) by BIOS. If validation fails, BIOS may print evil error message. source: sys/arch/i386/stand/mbr/mbr.S
   binary: /usr/mdec/mbr_*
   
2. MBR is executed; unless compiled with NO_BANNER, prints "NetBSD MBR Boot"
3. MBR loads PBR from 1st sector of active partition (or another disk, or another partition — if bootselector is used) CHS vs LBA: convert CHS start address to LBA, if matches LBA start - use CHS reads; otherwise - use LBA reads.
   "Error x"
   "No active partition" - self-explanatory
   "Disk read error"
   "No operating system" - first sector of active partition does not have magic number (0xaa55)
   "Invalid CHS read" - CHS vs LBA check selected LBA reads, but BIOS does not support them
   
4. PBR loads phase 1 bootstrap from next 15 sectors on disk, checks magic and runs it sys/arch/i386/stand/bootxx/pbr.S, /usr/mdec/bootxx_*
   '2' "Disk read"
   'B' "Not a bootxx image" - magic number wrong
   'P' "No NetBSD partition"
   'L' "Invalid CHS read" - CHS vs LBA check selected LBA reads, but BIOS does not support them
   
5. bootxx is executed, prints "NetBSD/{machine} {filesystem} Primary Bootstrap" sys/arch/i386/stand/bootxx/bootxx.S
   
6. bootxx loads phase 2 bootstrap (/boot): * from the start of MBR partition; or
   * from the start of MBR partition + raidframe offset; or
   * from the start of partition 'a' in disklabel.