The first device that starts up after pushing computer power button is PC power supply. If the supply voltages are in good working order, central processing unit will come into operation which reads out content of BIOS microcircuit and starts performing microcircuit-based Power-On Self Test or POST.
POST solves several basic problems.
1. Initializes and adjusts basic system composition: processor unit, chipset, internal memory and video display adapter.
2. Examines CMOS checksum and batteries’ condition. If the CMOS checksum is wrong, default values will be loaded.
3. Tests processor unit and internal memory. The testing results are usually displayed.
4. Initializes and adjusts hardware peripherals: keyboard, mouse pointing device, disk drive mechanisms, hard disks and others. Data about detected storage drives is usually displayed.
5. Distributes resources between peripherals and displays a datasheet with detected peripherals and appointed resources for them (Pic. 2.2).
Pic. 2.2. Final datasheet of POST procedure.
6. Searches and initializes peripherals from the BIOS.
7. Activates bootloader. When the successful POST procedure is accomplished, boot sector search, which can be located on the hard disk or removable media, starts. Peripherals inquest order is set with the help of parameters BIOS First Boot Device, Second Boot Device, Third Boot Device or related to them that are specified further.