POST stands for Power On Self Test. This is a function of your computer’s BIOS. The BIOS is a crucial system component that helps all of your devices coexist and communicate with your operating system. BIOS has many functions such as checking for information about your computer, loading device drivers, determining bootable drives, activating other BIOS chips (such as any on-board BIOS chips found on other devices), managing input and output of devices, and much more. The Power On Self Test is one of BIOS’s many duties.
You can see BIOS in action when you start your computer. The first thing BIOS does is perform the POST tests. This diagnostic procedure happens fairly fast and when all goes well, BIOS moves on to its other duties and eventually loads the operating system. Because the operating system isn’t loaded until after BIOS completes the start up routine, POST and BIOS errors usually come in the form of audible beeps. These beeps are necessary because the video display drivers and the operating system haven’t yet been loaded.
You’ll know that you have a hardware error if your computer stops loading at startup and simply beeps at you. As if Windows obscure error messages weren’t confusing enough, now you have a blank screen and a series of beeps to interpret!
The beeps will come at you much like Morse code. For example, one beep may mean that the system can’t access the system memory while two beeps may mean that the parity circuitry has failed. It’s important to note that POST codes vary depending on the manufacturer of the BIOS. Before you begin troubleshooting those pesky beeps, you’ll need to find out what type of BIOS you have and head to the BIOS manufacturer’s website in search of POST codes.
When POST runs into an error, the boot process normally comes to a screeching, or should we say “beeping,” halt. These errors are generally hardware failure errors of some sort.
Many computer repair techs use a POST diagnostics tool to further evaluate the POST test results. In addition to the audible beeps, POST generates extended troubleshoot codes that these POST diagnostics tools can decipher. The tech inserts the card into an available ISA slot and receives the data. A series of LED lights light up in various sequences depending on the problem. The tech then compares these codes to a master list and pinpoints the exact failure.
Using a diagnostic tool such as this is far more efficient then haphazardly removing and replacing devices. For example, what if you suspect memory failure, run out and buy new memory, install it, only to find your computer stills beeps at you during the POST test? You’ve just wasted your money on memory that you don’t need - and you still have the original problem.
Fortunately, most of the time, your computer will pass the POST test and everything will work as expected.
Celeste Stewart | June 6th, 2008
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