A computer running Windows Vista/7 can automatically fail over into the on-disk Windows RE only if a boot failure is detected. At startup, the Windows loader sets a status flag to indicate that the boot process has started, and this flag is typically cleared before the Windows logon screen is displayed. If the boot attempt fails, the flag is not cleared. The next time the computer starts, the loader detects the flag and assumes that a boot failure occurred. When this happens, the loader launches Windows RE instead of Windows Vista/7
Because the failover mechanism relies on the Windows boot manager and Windows boot loader, some failures will render Windows RE inaccessible. In the following scenarios, the user must use bootable Windows RE media to recover the computer:
* Disk metadata corruption in the master boot record (MBR), partition table, or boot sector of Windows RE partition.
* Missing or corrupt boot manager.
* Missing or corrupt boot configuration data.
Sometimes the boot status flag cannot be read or written to by the boot loader, in which case Windows will not automatically fail over into Windows RE. However, the user can still manually launch into the on-disk Windows RE through the F8 menu.