POWER-ON SELF-TEST (POST) AND ERROR CODES

The Power-On Self-Test (POST) is a self-diagnostic program that runs a test on RAM, I/O devices, and the CPU on system startup. The POST is stored in the ROM BIOS and requires at least a processor, memory, and video adapter to complete its diagnostic tests. The POST recognizes errors related to BIOS configuration settings and I/O connectivity, such as a stuck keyboard. Be forewarned: you may be asked to identify errors the POST might not recognize. Table 15.3 lists some examples of POST numeric error codes that you may encounter while using a computer. There is a good chance you may also encounter one or two POST numeric error code questions on the test.

Table 15.3: Common Post Error Codes

Error Code	Error Associated with Code
1XX	System board error
201	Memory error
301	Keyboard error
5XX	Monitor error
601	Floppy drive/adapter error
1101	Serial card error
1701	Hard drive controller error

There are also sounds or beep codes associated with POST operations and system startup to alert you in the event of an error. BIOS manufacturers, such as IBM, Phoenix, and Award, each provide their own distinct set of beep codes. A list of IBM’s common beep codes is provided in Table 15.4. It is likely that the test will focus on numeric error codes. If you are interested in learning more about beep codes specific to BIOS manufacturers that are not listed, you should consult that manufacturer’s Web site.

Table 15.4: Common IBM Beep Codes

Beep Description	Error Associated with Beep
No beep	Motherboard or power failure
One short beep	All POST operations completed successfully
Two short beeps	POST error
One long beep, one short beep	Motherboard error
One long beep, two short beeps	Video adapter failed
One long beep, three short beeps	Video adapter error
Three long beeps	Keyboard failure