Upgrading And Repairing PCs 21st Edition: PC Diagnostics

The POST

The POST

Although the diagnostics performed by the system POST are not thorough, they are the first line of defense, especially when it comes to detecting severe motherboard problems. If the POST encounters a problem severe enough to keep the system from operating properly, it halts the system boot process and generates an error message that often identifies the cause of the problem. These POST-detected problems are sometimes called fatal errors because they prevent the system from booting.

Systems that use UEFI firmware also perform diagnostics tests, but depending upon the specific firmware in use, error messages may be stored in event logs, and beep codes may be used for some errors.

How Errors Are Displayed

The POST tests normally provide three types of output messages: audio codes, onscreen text messages, and hexadecimal numeric codes that are sent to an I/O port address.

POST errors can be displayed in the following three ways:

  • Beep codes—Heard through the speaker or beeper attached to the motherboard. Note that some systems do not include a speaker.
  • POST checkpoint codes—Hexadecimal checkpoint codes sent to an I/O port address. A special card plugged into an available expansion slot is required to view these codes.
  • Onscreen messages—Error messages displayed onscreen after the video adapter is initialized.

Systems that use UEFI firmware might use beep and checkpoint codes but also store error messages in event logs.

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Upgrading and Repairing PCs: 21st Edtion

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