Can anyone tell me how do I understand what happens when you boot up a Unix system? Like "BIOS" is loaded, it does a peripheral test etc until you get a shell?
For each unix it's different but for linux, from bios you go the bootloader (u-boot, lilo, grub..) then the kernel decompress itself, start himself and call init once booted.
This article explain well the process : http://www.ibm.com/developerworks/linux/library/l-linuxboot/