POST (Power-On Self Test)

POST—Power-On Self Test

The system BIOS program starts by invoking a special program (stored in a ROM chip) called POST.ROM BIOS run the POST program that automatically performs a series of tests that check the primary component in the system, such as the CPU, RAM, motherboard support circuitry, memory and major peripherals such as expansion chassis etc. POST program is executed before the loading of the operating system.

The POST has two stages.
 
§ Test 1 occurs before and during the test of the video.
§ Test 2 occurs after the video has been tested.