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Reading BIOS Error Codes

Because beep codes can indicate only some of the problems in a system at startup, most BIOSes also output a series of status codes during the boot procedure. These codes are sent to an I/O port address that can be read by specialized diagnostic cards, which you can purchase from many different vendors. These POST cards (so named from the power-on self test) feature a two-digit LED panel that displays the status codes output by the BIOS. The simpler POST cards are hard-wired to pick up signals from the most commonly used I/O port address 80hex, but more expensive models can be adjusted with jumper blocks to use other addresses used by certain BIOSes (such as Compaq).

These cards are normally sold with manuals that list the error/status codes. Although the cards are durable, the codes can become outdated. To get an updated list of codes, contact the system or BIOS vendor's Web site.

Most POST cards have been based on the ISA bus, but the latest models are now being made to fit into PCI slots because ISA is becoming obsolete. For diagnosing portable systems, and to avoid the need to open a system to insert a POST card, Ultra-X offers a MicroPOST display unit that attaches to the parallel port. Contact Ultra-X at http://www.uxd.com for more information. For standard ISA and PCI POST cards, see JDR Computer Products at http://www.jdr.com.

Onscreen Error Messages

An onscreen error message is often the easiest of the error methods to understand because you don't need to count beeps or open the system to install a POST card. However, because some systems use numeric error codes, and because even "plain English" codes need interpretation, these messages can still be a challenge to interpret. Because the video circuits are tested after components such as the motherboard, CPU, and BIOS, an onscreen error message is usually indicative of a less-serious error than one that is reported with beep codes.

Interpreting Error Codes and Messages

Because beep codes, error/status codes, and onscreen messages vary a great deal by BIOS vendor (and sometimes BIOS model), you must know what BIOS a system has before you can choose the correct table. With major-brand systems (and some others), you'll typically find a list of error codes and messages in the system documentation. You can also contact the BIOS or system vendors' Web sites for this information, or check the CD included with Upgrading and Repairing PCs, 13th Edition, published by Que.

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