What is Last Known Good Configuration ?

The Last Known Good configuration" is one of the methods which are used to repair our computer system. In this method a restore of data from the backup is not required. This "last known good configuration" is a backup replica of the existing configuration which is stored on the registry key "HKLM\System\CurrentControlSet". This registry key is always updated whenever the system is shut down by the user after successfully and effectively logging on. Our system can be repaired by restoring information from this updated registry key. For instance in case when we install some driver which causes our operating system not to be loaded, this type of repair is helpful and useful. 

So it is a very good practice to repair our system without any loss. So whenever we see our operating systemfails to load, simply press F8 and when the message "please select the operating system to start" appears, just select the Last Known Good Configuration. This option can be seen under the "Windows Advanced Options Menu". The Last Known Good Configuration is only useful in the case if we have not logged on yet. Whenever we logon and then shut down or even restart, all of the current configurations always become the "Last Known Good Configuration".