Order Of Linux (X86) Startup Power On - the CPU is initialized, and passes control to a program located in a given memory address - normally the BIOS. POST - The BIOS performs a "Power-On Self Test", to check that the basic hardware is there (memory, keyboard, disk controllers, etc). OS Loader - The BIOS loads an OS loader off the MBR of the hard drive, or off sector number 0 of the 'active partition' of that drive.