Last Known Good Configuration is used when XP has been just changed by adding hardware or software that is incompatible with XP, has configuration settings that conflict with XP or other hardware/ software, or an important service such as the one used to initialize SCSI (Small System Computer Interface) hard drives has been accidentally disabled. It reverses the most recent changes that have been made since the last successful XP boot. Whenever XP boots successfully (without any problems), a copy of the Clone control set is made to be used if the Last Known Good Configuration options is chosen. A control set is a registry sub key located under HKEY LOCAL MACHINE System and contains information about devices and services. To access Last Known Good Configuration, press the F8 key during the boot process and select the LastKnownGood Configuration option from the Windows Advanced Options menu.

Whenever, the Last Known Good Configuration option is used, all configuration changes made since the last successful boot are lost. However, since the changes are the most likely cause of XP not booting correctly, Last Known Good Configuration is a useful tool when installing new devices and drivers that do not work properly. If Last Known Good Configuration does not work properly, boot the computer into Safe Mode, which is covered in next section.