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Updated on July 31, 2016


POST is the process where a set of pre-installed instructions found on BIOS chip (BASIC INPUT OUTPUT SYSTEM) configured with the aim of checking and inspecting every hardware components found in a computer machine.

The above process i.e POST works when the computer machine is powered on thus the BIOS onwards will initialize the POST process immediately.

POST therefore is a diagnostic process that can sort out any defects found on the computer system including its hardware and software issues.For example, memory issue or RAM issue; maybe a faulty RAM and so on.

For the user or the person using the computer to know and understand whats going on in the computer system (diagnostic), the POST process in conjunction with the BIOS warns the user with various ways:

  1. Through beep codes that could be heard by the user via BIOS speaker mounted on the motherboard.Every manufacturer has their unique beep sound corresponding a certain defect like 2 beep codes shows a faulty RAM in some of the machines.
  2. Through text error message shown on the screen i.e monitor.An error like 'drive failure' meaning hard drive was not detected by the BIOS or a faulty hard drive.
  3. Through LED light indicators that are located on the front panel of a system unit.Power LED indicator can somehow blink a red color showing that processor is faulty.
  4. Through flashing of special keys indicators on the keyboard i.e NUM LOCK,CAPS LOCK and SCROLL LOCK. A machine can flash NUM LOCK showing memory(ram) problem.
  5. When all these special warning signs fail to occur, a certain expansion card is used known as POST EXPANSION CARD; where it is a diagnostic tool that can be installed on PCI slots when the computer fails to display error codes on the screen itself or fails to beep.It comprises of a LED screen showing number codes that could show a certain defect on a computer in according to its manufacturer.

NOTE: When POST process is completed successfully i.e computer hardware is functioning okay, BIOS afterwards looks for operating system and hand over the responsibility to operating system for the rest of operation.


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      Eric 5 weeks ago

      Great article learnt alot from it:)