Each time a user turns on his or her computer, the BIOS gathers information about the major system components and performs a special test called the Power On Self Test (POST) to make sure that each component is functioning correctly. If the test identifies a hardware problem, the BIOS will display an error message on the monitor. But, if the failure occurred before the BIOS could access the video card, the BIOS will issue special beep codes to alert the user to the problem.
In this article, I'll take a detailed look at the beeps that are issued by various BIOS manufacturers, and I'll provide you with a resource for more detailed information. Understanding these noises will allow you to troubleshoot a multitude of hardware problems.
Annoying noises, flashing lights
During a POST session, your computer has several ways to communicate: Either through flashing indicator lights, the computer's speaker, or via the monitor. Since the monitor is not initialized until later in the process, early failures are communicated by red or absent status lights, such as the power and hard drive activity lights, or by sound in the form of beeps.
POST diagnostic cards
Another option is to purchase a POST diagnostic card to intercept POST errors at their source via the ISA or PCI bus. Cards are available for either bus and typically contain one or two digital readouts that present the codes, as well as LEDs for monitoring the power supply. Since POST codes are more numerous than beep codes (there may be 10 beep codes to 256 POST codes), a diagnostic card can help you track the progress of the POST and see more detail about what caused a failure or warning.
An ISA card is preferred, as it's possible that a PCI card may not report all the POST codes. Because the ISA bus is initialized first, the PCI bus only receives the codes generated after the ISA bus is initialized. In addition, ISA busses connect to the South Bridge chip, so damaged motherboards may not be able to send codes to the PCI bus at all.
You can obtain more information on POST diagnostic cards from manufacturers such as Xetal Systems Inc., makers of POSTmortem; Microsystems Development Technologies Inc.'s Post Code Master, or by running a Web search.
Heard any good beeps lately?
Naturally, if the speaker is damaged or disconnected, you'll have no way of knowing what ails your hardware without a diagnostic card. At the conclusion of a successful POST, the computer should beep once or twice. These beeps inform you that your hardware is in good working order. If you don't hear this "all's well" beep, here are a few things to check:
- Are external speakers connected? On many computers, the computer speaker is disabled when a jack is connected.
- Is the volume too low? Use the function keys indicated by the manufacturer to increase the volume.
- Did someone disconnect the speaker? People do this occasionally because the beeps bother them. Reconnect the leads to the motherboard jumpers.
- Is the onboard speaker disabled in the BIOS? Re-enable the speaker in the BIOS setup program. Note: It's also a good idea to include a small speaker mounted to a motherboard with some standard leads as part of your troubleshooting kit.
To create unique error messages, codes emit combinations of long and short beeps, similar to Morse code. Instead of letters, however, each unique sequence indicates a different problem with components. As you might have guessed, in contrast to a universal standard such as Morse code, each BIOS manufacturer creates its own beep sequences.
Below are audible codes for several common BIOSs that I obtained from The BIOS Companion. The Companion excels in presenting almost every BIOS setting that can be configured. It also contains tables of POST codes. It can be purchased online (as a PDF file) for $15 or printed for $49.95, or it can be acquired as part of a larger set, called The PC Engineer's Reference Book. You'll want to check this out if you support many different PC types, including legacy equipment. For more information on these and other reference books, see Electrocution Technical Publishers.
American Megatrends Inc. BIOS
Standard beep codes for computers using American Megatrends Inc. (AMI) BIOSs are listed in Table A.
|American Megatrends Inc. BIOS beep codes|
Award BIOSs only have one beep code: One long beep, followed by two short beeps, indicates that the BIOS is unable to initialize the video screen.
Standard beep codes for Compaq computers with no text and error message are shown in Table B.
|Other Compaq beeps are associated with specific text messages on the video screen.|
Beep codes for Dell computers (Phoenix BIOS) are listed in Table C. (All are short beeps separated by pauses.)
|To view screen messages that accompany beep codes, make sure the Phoenix QuietBoot feature is disabled by pressing [Esc] during boot. This will display POST messages.|
IBM beep codes
IBM personal computers (Thinkpads and Desktops) use a Phoenix-based BIOS. An extensive amount of information can be gleaned from the beep codes of Phoenix BIOSs. Since 1994, Phoenix has used a four-part system: four bursts of short beeps separated by pauses. For example, in Table D below, a value such as 4-2-3-1 (shutdown error), means four short beeps, pause, two short beeps, pause, three short beeps, pause, one short beep. While the codes in the table below will apply in general, to be sure, always check the specification for your particular model. The beep codes for IBM computers are listed in Table D. (All are short beeps separated by pauses.)
Do they really help?
If a system error is occurring before video initialization, interpreting the BIOS beep codes is your last line of defense when something is troubling your system. All you need to do is listen closely to the sequence of beeps for your specific BIOS and simply look up the corresponding error description. Then, you can focus your troubleshooting efforts on that particular problem instead of wasting time with guesswork.