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Power On Self Test (Owned by BIOSMAN Inc.)

What is a Power On Self Test (P.O.S.T.)? This site is dedicated to answering that and other BIOS (Basic Input Output System) related questions. Every computer has a BIOS. Every BIOS outputs the POST. Understanding what happens to your computer during this stage is key to obtaining better peformance and for troubleshooting all problems with your PC.

1. What is the Power On Self Test?
POST explained cont...

I think now is a good point to take a step back. There are three main BIOS vendors: AMI (American Megatrends Inc.), Phoenix and Award.

Each company has its own set of beep codes and POST codes.

NOTE: Whenever I refer to POST I mean Power On Self Test.

Read on for more general information about the Power On Self test or jump over to section 1 for POST codes or Section 3 for Beep codes.

The Power On Self Test is activated by the BIOS. It runs a series of checks and diagnostics on your motherboard. Some of the items it checks are, keyboard, CPU, memory, PCI slots etc. Keep in mind most POST problems are related to memory. From experience no matter what POST code or beep code I get I always check memory first. I have found most problems arise in this order:

1. Memory

2. Power supply

3. Heat/Cooling

4. Hardware


I would say that 95% of all the problems I have faced in 9 years of working with motherboards were related to those 5 items and in that order.

The Power On Self Test diagnoses and provides information on all 5. The Power On Self test is designed to help troubleshoot problems with your computer. Whenever something goes wrong, assuming we are talking about a fonce functional system, the first thing to ask yourself is:

1) what did I change? Obviousely if you changed anything, go back. If it s was aBIOS upgrade and it failed then you can order a new BIOS from this link: BIOS update. You can also try the recovery techniques found in the BIOS recovery methods found here: BIOS recovery

Lets say you didnt chnage anything, then the question changes to:

2) What could have changed?

The answers to this are too many to list but always start with the 5 items above in order. Once again ther Power On Self Test can help you narrow this down. If the board just stopped working suddenly I always suspect overheating. Most CPU's have a built in shut down feature built in. Foe Intel CPU's its around 100C. Thatt's pretty darn hot. usually you will see a slow down in performance before this occurs. Its mostly caused by CPU fans failing. This problem will not be identified in the Power On Self Test though. Easiest way to find out if this is your problem? Basically once the CPU is cool enough it will boot again. YOu could also viisually check the that when you turn it on the fans are spinning. I had one client who's system had this problem intermittemntly. Once I opened the chassis it was obviiuos. There was a herd of dust bunnies hiding in his case and the fan had collected enough that it was unable to spin.

What else could have changed? Well read the POST codes or listen to the beep codes. Its time for you to go back and read about each. Now due to the fact most people won't have POST cards, I suggest going to the beep code section first. You can click 'back' on your browser or click here: beep codes. If you want to jump straight into POST codes click here: POST Codes.

Some problems will cause the Power On Self Test to not function at all. The most common reason for the POST to not occur is a BIOS failure. ( assuming power supply is working). There are many reasons for the BIOS to fail. Most common is a failed BIOS flash. YOu would be very surprised at how many BIOS flash failures occur. Other reasons for BIOS failure are, BIOS corruption due to virus or malignant code, static charge, electrical surge, and physical damage to pins,. I am sure there are others like those pesky gremlins that inhabit your PC or even lonely dust bunnies trying to get friendly with your BIOS chip.

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