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The POST Process

With the primary part of the BIOS now loaded to RAM, the POST process begins. If any fatal problems that prevent the PC from operating normally are found, beep codes sound or if the fault is after the video adaptor BIOS has loaded an error message displays, and the boot process stops.

Video adapter BIOS loads

If all is well, the boot sequence continues and the system BIOS loads the device BIOS of the video adapter (if there is one) and loads it to memory.

As your PC boots, the video adapter's information displays on the monitor.

Device BIOS loads Any other device-specific BIOS routines, such as those for the hard drives or SCSI devices, are loaded.
System tests the devices The system determines whether the devices listed in the CMOS configuration data are present and functioning, including tests for device speeds and access modes.
Ports are assigned identities The serial and parallel ports are assigned their identities (such as COM1, COM2 and LPT1), and a message is displayed for each device found, configured and tested. PnP devices detected are configured.
Configuration is confirmed The BIOS displays a summary screen that details the computer as the BIOS sees it.
Storage devices are checked The CMOS data contains the sequence in which storage devices are to be checked by the BIOS to locate which drive holds the operating system and verifies the data in the CMOS with respect to the physical devices it can detect in the system.

Next: Decoding POST Messages