A beep code is the audio signal given out by a computer to announce the result of a short diagnostic testing sequence the computer performs when first powering up (called the Power-On-Self-Test or POST). The POST is a small program contained in the computer's Basic Input/Output Operating System (BIOS) that checks to make sure necessary hardware is present and required memory is accessible. If everything tests out correctly, the computer will typically emit a single beep and continue the starting-up process. If something is wrong, the computer will display an error message on the monitor screen and announce the errors audibly with a series of beeps that vary in pitch, number and duration (this is especially useful when the error exists with the monitor or graphic components). The beeping sequence is really a coded message (beep code) designed to tell the user what is wrong with the computer.
There is no official standard for beep codes; audio patterns vary according to the manufacturer of the computer's BIOS program. If an error message is beeped on startup, the user must first determine what kind of BIOS the computer is running (Phoenix or AMI are the most popular) and use that information to look up the particular beep code sequence that is being sent. BIOS information and beep code interpretations can be found in the manual that comes with the computer and on the manufacturer's Web site.