Computer System Error Beep Codes

Power On Self Test Beep Codes

The computer POST (Power On Self Test) is the process of testing the computer system, insuring that it meets the necessary system requirements and that all hardware is working properly before starting the remainder of the boot process. If the computer passes the POST, the computer will have a single beep (with some computer BIOS manufacturers it may beep twice) as the computer starts and the computer will continue to start normally. However, if the computer fails the POST, the computer will either not beep at all or will generate a beep code, which tells the user the source of the problem.

Each time the computer boots up the computer must past the POST. Below is the common step a POST performs each time your computer starts.

1. Test the power supply to ensure that it is turned on and that it releases its reset signal.
2. CPU must exit the reset status mode and thereafter be able to execute instructions.
3. BIOS checksum must be valid, meaning that it must be readable.
4. CMOS checksum must be valid, meaning that it must be readable.
5. CPU must be able to read all forms of memory such as the memory controller, memory bus, and memory module.
6. The first 64KB of memory must be operational and have the capability to be read and written to and from, and capable of containing the POST code.
7. I/O bus / controller must be accessible.
8. I/O bus must be able to write / read from the video subsystem and be able to read all video RAM.

If the computer does not pass any of the above tests, your computer will receive an irregular POST. An irregular POST is a beep code that is different from the standard one or two beeps. This could be either no beep at all or a combination of different beeps indicating what is causing the computer not to past the POST.

Example of a Computer Error Beep Codes

Beep Code	Description of Problem
No Beeps	Short, No power, Bad CPU/MB, Loose Peripherals
One Beep	Everything is normal and Computer POST is fine
Two Beeps	POST/CMOS Error
One Long Beep, One Short Beep	Motherboard Problem
One Long Beep, Two Short Beeps	Video Problem
One Long Beep, Three Short Beeps	Video Problem
Three Long Beeps	Keyboard Error
Repeated Long Beeps	Memory Error
Continuous Hi-Lo Beeps	CPU Overheating