Power-on Self Test (POST)

Definition of Power-On Self Test (POST) in the Network Encyclopedia.

What is Power-On Self Test (POST)?

Power-On Self Test is a special set of ROM routines that run whenever a PC is booted. The power-on self test (POST) is designed to test whether system components are functioning properly before attempting to boot the operating system, and checks such things as the RAM, keyboard, and disk drives.

Power-on Self Test (POST)
Power-on Self Test (POST)

If a problem is detected during the POST, the system typically emits a series of beeps and displays a corresponding error message giving some indication of the problem.

Specific problems are indicated by different numbers of beeps, but the interpretation of these varies depending on the BIOS used.


On newer Pentium II or III systems that use the popular AMI WinBIOS, use the following table to interpret the number of beeps in order to troubleshoot the problem.

POST Beep Codes for AMI WinBIOS

Number of BeepsProblemResolution
1, 2, or 3Memory errorCheck speed and voltage of dual inline memory modules (DIMMs), try reseating DIMMs, or replace DIMMs
4Timer errorReplace motherboard
5CPU errorTry replacing CPU, or replace motherboard
6Gate A20 errorTry reseating keyboard controller chip, try replacing keyboard controller chip, or replace motherboard
7Interrupt errorReplace motherboard
8Video memory errorTry reseating the video RAM (VRAM), try replacing the VRAM, or replace video card
9BIOS ROM errorReplace BIOS ROM chip


Articles posted after being checked by editors.

Recent Content

link to Simplex


Simplex is a form of communication in which signals are sent in only one direction. This is different from duplex transmission, in which signals can simultaneously be sent and received by a station, and from half-duplex transmission, in which signals can be sent or received but not both at the same time.
link to Full-duplex


Full-Duplex is a mode of communication in which data is simultaneously transmitted and received between stations. Full-duplex communication is twice as fast as half-duplex communication, and typically uses two separate pairs of wires (or two channels for wireless networking) for supporting simultaneous transmission and reception by a host.