The POST Process

Immediately after the BIOS programs are loaded to memory, the POST (Power-On Self-Test) starts. The POST performs a check of the system components and hardware listed in the system setup(CMOS) data are present and tests to see that they are functioning properly. The POST process is done before the BIOS begins its startup procedures. The POST process is fast and is typically unnoticed provided there are no problems. If the POST finds problems, it signals with beep codes (beeps emitted though the system speaker) indicating the source of the problem. At the time the POST runs, it has no other means of signaling problems because none of the hardware I/O functions have been loaded. The display and printer are not available, so the system speaker, which is technically a part of the motherboard, is the only means the POST has of signaling what is going wrong

Depending on the cause of the error, the POST routine uses an established beep pattern to signal the type of problem encountered. The beep codes are similar to a POST Morse code. The pattern and meaning of the combinations of short and long beeps is unique to the BIOS’ manufacturer. However, nearly all POST problems are fatal errors because the POST is testing only essential system components.

BIOS Beep Codes

Not all beepcodes mean something bad. Nearly all BIOS programs will sound a single beepcode to indicate that all is well and then continue the boot process. However, if the boot process does not continue, the single beep has a different meaning or there were additional codes you didn’t hear. You may need to cold boot the PC at least once to hear all of the beeps. Often the beep codes catch you by surprise the first time they are sounded. Once you are sure you have heard all of the beeps, the next step is to figure out what they mean.

Each BIOS producer has its own collection of POST error beep codes, but the four primary beepcode sets are IBM standard, AMI, Award, and Phoenix. As is illustrated in Tables 6-1 through 6-4, there is no standard beepcode set. Each set of beepcodes has a different sound pattern to indicate different problems. The different beep code sets involve short beeps, long beeps, and a varying number of beeps in a three- or four-beep series.

Actually, the codes listed in Table 6-3 are only possible examples of Award BIOS’ beepcodes. Award relies on motherboard manufacturers to generate the beepcodes used with its BIOS. So, if you have an Award BIOS on your PC, you’ll need to check with its manufacturer or the manufacturer of its motherboard to get a list of the beepcodes in use.

The Phoenix BIOS POST error beepcodes, listed in Table 6-4, are more complicated than most other beepcode sets. When an error is detected, the first set of beeps is sounded followed by a slight pause before the next set of beeps, and so on. For example, the beep code pattern that indicates that the BIOS itself may be corrupt is 1-1-4. This would sound something like beep, pause, beep, pause, beep, beep, beep, beep.