power-on self test (POST)

Definition of power-on self test (POST) in The Network Encyclopedia.

What is power-on self test (POST)?

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.

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 Beeps Problem Resolution
1, 2, or 3
Memory error
Check speed and voltage of dual inline memory modules (DIMMs), try reseating DIMMs, or replace DIMMs
Timer error
Replace motherboard
CPU error
Try replacing CPU, or replace motherboard
Gate A20 error
Try reseating keyboard controller chip, try replacing keyboard controller chip, or replace motherboard
Interrupt error
Replace motherboard
Video memory error
Try reseating the video RAM (VRAM), try replacing the VRAM, or replace video card
BIOS ROM error
Replace BIOS ROM chip