1. Stage 0: Master Boot Record
  2. Stage 1: Partition Boot Record, bootxx
  3. Stage 2
  4. Glossary
  5. See also
  6. References

Stage 0: Master Boot Record

MBR is read by the BIOS and then validated (checked for magic number 0xaa55 at the end). If validation fails, BIOS may print evil error message and/or try next boot device; otherwise, BIOS passes control to MBR.

Unless it was compiled with NO_BANNER, MBR displays its banner: "NetBSD MBR Boot". Next, it checks if CHS or LBA addressing must be used in further BIOS I/O calls. Since partition table entry stores both linear and CHS address, linear address is computed from CHS address, and if it matches stored linear address - MBR will use CHS addressing. LBA addressing will be tried otherwise, even if it is not supported by BIOS.

PBR is then loaded from 1st sector of active partition (or, if boot selector was compiled into this MBR, it may be loaded from another partition or disk).

Stage 1: Partition Boot Record, bootxx

PBR loads phase 1 bootstrap (bootxx) from next 15 sectors on disk, validates and runs it.

bootxx displays its banner: NetBSD/(machine) (filesystem) Primary Bootstrap and tries to load phase 2 bootstrap (boot2) from several locations:

Stage 2



 Basic Input-Output System 


 Main Boot Record, stored at LBA 0 


 Partition Boot Record, stored in first sector of bootable partition 


 Cylinder, Head, Sector addressing 


 Linear Block Address[ing] 

See also