.\"	$OpenBSD: biosboot.8,v 1.4 1997/09/05 21:25:15 weingart Exp $
.\"
.\" Copyright (c) 1997 Michael Shalayeff
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
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.\"    must display the following acknowledgement:
.\"	This product includes software developed by Michael Shalayeff.
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.Dd September 1, 1997
.Dt BIOSBOOT 8 i386
.Os OpenBSD 2.1
.Sh NAME
.Nm biosboot
.Nd
primary system bootstrap program
.Sh DESCRIPTION
This small program (roughly 256 bytes of code) is responsible for
loading the second stage
.Xr boot 8
program, which in turn, will load the kernel.
It is a small piece of code that takes no input or options.
.Pp
The location of the
.Xr boot 8
program that
.Nm
loads, is stored in a block table inside the
.Nm
program.  The
.Xr installboot 8
program is used to fill this table with the location of the
.Nm
program.  This location is BIOS dependant, so you have to run the
.Xr installboot 8
program to update this table every time you move your disk between
machines and/or controllers.
.Pp
When 
.Nm
receives control from either the BIOS or the MBR it will print the message:
.Pp
.Dl loading /boot
.Pp
followed by a dot for every successfully loaded block,
and then put cursor on the next line right before switching into
protected mode and transferring control to the just loaded /boot program.
.Sh DIAGNOSTICS
Diagnostics consist of two error messages:
.Bl -tag -width read_error_
.It Er Read error
Some kind of error returned by the BIOS read call. This might be
any media error, including bad sectors (common on floppy disks),
and invalid sectors (can occur with messed up geometry translations).
.It Er Bad magic
The just loaded /boot image contains a bad magic in it's header.  This
might indicate some kind of hardware problem,  or it may mean that the
.Ar boot
argument to the
.Xr installboot 8
command was not a valid /boot program.
.El
.Pp
Other common reasons for these errors to appear is that a wrong BIOS geometry
has been used in
.Xr installboot 8
for the device you are booting from.
.Sh NOTES
The practice of making OpenBSD use the whole disk (ie: having
.Nm                                                                            
as the MBR) has been depreciated, and will not work on certain BIOS versions.
There is a lot of strange behaviour with different BIOS's, one of well
known lobotomy cases is that the BIOS does not pass the right boot drive
number to the
.Nm
program.  This is one of the main reasons that having
.Nm
as the MBR has been depreciated.
.Sh FILES
.Bl -tag -width /usr/mdec/biosbootxx -compact
.It Pa /usr/mdec/mbr
Master Boot Record block
.It Pa /usr/mdec/biosboot
primary bootstrap
.It Pa /boot
secondary bootstrap
.It Pa /bsd
system code
.El
.Sh SEE ALSO
.Xr boot_i386 8 ,
.Xr fdisk 8 ,
.Xr installboot 8 ,
.Xr boot 8 .
.Sh BUGS
It contains a fake partition table and associated things that it should not.
.Pp
It should do a checksum over the loaded /boot image, and check that against
a value that
.Xr installboot 8
has precomputed.
.Pp
There is no BIOS error number reported nor is the location of the error
reported.
.Pp
You can pick your motherboard, and you can pick your BIOS,
but you can't pick your motherboard's BIOS.
.Sh HISTORY
This program was written by Michael Shalayeff for OpenBSD.
However it's based on bootstrap code from older versions of this
operating system, other operating systems, other programs, and
other people's work.