Upgrading And Repairing PCs 21st Edition: PC Diagnostics

BIOS POST Beep Codes, Checkpoint Codes, And Onscreen Messages

BIOS POST Beep Codes

Beep codes are used for fatal errors only, which are errors that occur so early in the process that the video card and other devices are not yet functional. Because no display is available, these codes take the form of a series of beeps that identify the faulty component. When your computer is functioning normally, you may hear one or two short beeps when the system starts up at the completion of the POST, although depending on the system, it may not make any sounds at all if things are normal. If a problem is detected, a different number of beeps sound, sometimes in a combination of short and long tones. Some implementations of UEFI firmware also use POST codes to report errors.

BIOS POST Checkpoint Codes

POST checkpoint codes are hexadecimal numeric codes written by POST routines to I/O port address 80h as each major step is begun. These are often simply called POST codes. These POST codes can only be read by a special adapter card plugged into one of the system slots. These cards originally were designed for system manufacturers to use for burn-in testing of the motherboard. Several companies make these cards available to technicians; if you search for “post code card,” you will find many that are available.

POST checkpoint codes can track the system’s progress through the boot process from power-on right up to the point at which the bootstrap loader runs (when the operating system load begins). When you plug a POST code reader card into a slot, during the POST you see two-digit hexadecimal numbers flash on the card’s display. If the system stops unexpectedly or hangs, you can identify the test that was in progress during the hang from the two-digit code. This step usually helps to identify the malfunctioning component.

Originally, most POST reader cards plugged into the 8-bit connector that is a part of the ISA or Enhanced Industry Standard Architecture (EISA) bus. The motherboards found in modern PCs have no ISA slots, so obviously an ISA POST card won’t work. Fortunately, the companies that make POST cards make PCI or even PCI Express versions (see the figure below). There are even Mini PCI and Mini PCI Express cards available for testing laptop motherboards.

AMI markets a USB-based diagnostic device called the AMIDebug RX to display checkpoint and error codes for its AMIBIOS and Aptio 4.x firmware.

Note: You can find listings for additional POST checkpoint codes postcodemaster.com. Remember to consult your motherboard documentation for codes specific to your BIOS version.

The PC Diag Inc PCISA FlipPOST diagnostics card works with both PCI- and ISA-based systems, and it tests motherboard voltage levels.

BIOS POST Onscreen Messages

Onscreen messages are brief messages that attempt to indicate a specific failure. These messages can be displayed only after the point at which the video adapter card and display have been initialized.

These different types of error messages are BIOS dependent and vary among BIOS manufacturers, and even in some cases among different BIOSs from the same manufacturer. The following sections list the codes used by the most popular ROM BIOS versions (AMI, Award, Phoenix, and IBM BIOS), but you should consult your motherboard or ROM BIOS manufacturer for the codes specific to your board and BIOS.

Most POST code cards come with documentation listing the POST checkpoint codes for various BIOS versions. If your BIOS is different from what I have listed here, consult the documentation for your BIOS or the information that came with your particular POST card.

Upgrading and Repairing PCs: 21st Edtion