Assuming BIOS is what boots bootsector or program from nothing - turning PC on from programming level.

I found 1 link google:
http://www.paulcilwa.com/writing/technical/03.assembler/BootSector/index.asp

and another

http://www.supernovah.com/Tutorials/BootSector2.php

[BITS 16]
[ORG 0x7C00]

jmp $

times 510 - ($ - $$) db 0
dw 0xAA55

Article that shows how Visual Studio builds and modify's linux kernel.

http://sysprogs.com/VisualKernel/tutorials/kernel/

wut?

WHAT LOCKS YOUR SCREEN IN XFCE

#!/bin/sh
#
#  xfce4
#
#  Copyright (C) 1999, 2003 Olivier Fourdan (fourdan@xfce.org)
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software
#  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
#

if pgrep xscreensaver > /dev/null 2>&1; then
    xscreensaver-command -lock
elif pgrep -f gnome-screensaver 2>/dev/null; then
    gnome-screensaver-command --lock
elif test x"`which slock 2>/dev/null`" != x""; then
   slock
else
    xlock $*
fi
exit 0