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