When Windows has finished installing the system core on your hard disk or virtual hard disk, the preinstallation environment (
Windows PE) which took care of the installation has done its job. A WinPE is like a mini operating system, taking care of vital system functions so that the real OS can be installed, analyzed or repaired. The WinPE checks its own checklist and if all lights are green, hands over the control to real Windows.
Windows thanks WinPE and boots first time. This first boot is called an
OOBE boot,
OOBE Mode (Out-Of-Box Experience), also known as Welcome Mode. To put it very simple it is (usually) a first ever boot after installation. If you buy a new computer with preinstalled Windows and turn it on, what you see and experience is OOBE Mode: Windows is there, ready to serve you but there's no user accounts yet, no personal data, nothing. A virgin Windows installation.
What we want now is to tell Windows "
Sorry, I would like to do some stuff before entering OOBE". Windows accepts our request and let's us reboot to so called
Audit Mode, kind of mix of WinPE and OOBE. Not WinPE per se but clearly not OOBE, either.
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Windows reboots now, rebooting to Audit Mode. It uses a so called
built-in administrator user profile.
Audit Mode alone is nothing, can nothing. A built-in native Windows tool called
System Preparation Tool (noun = Sysprep, verb = to sysprep) is needed to tell Audit Mode what to do. As soon as Windows shows the desktop in Audit Mode, it asks Sysprep to come to help as Audit Mode understands that although powerful together with Sysprep, alone it could do nothing.