Windows Preinstallation Environment

Windows Preinstallation Environment, often shortened to WinPE or Windows PE, is a minimal version of Windows typically used for system deployment or recovery. It is configured in such a way that changes made to the environment do not persist across reboots, which makes it possible to boot it from read-only media such as CD-ROM discs or across the network. It was first introduced in Windows XP as a replacement for MS-DOS-based boot disks and has since been adopted for the setup and the recovery environment starting with Windows Vista. The Microsoft Validation OS, introduced alongside the Windows 11 2022 Update, is also based upon the Preinstallation Environmnet, although it is stripped down to the bare essentials required to bring up the Windows GUI and console.

In Windows XP, the environment is loaded by  in a similar manner to the text mode setup. However, it does not load the operating system into a RAM disk by default and therefore it is required to keep the system disk in the drive, as ejecting it would cause the system to misbehave. In Windows Vista, the system is stored inside a WIM file called, which is loaded by the boot manager into a RAM disk and then executed. Unlike regular versions of Windows, Windows PE uses the  switch to instruct the kernel to load registry hives as volatile to ensure that the operating system does not attempt to save any registry changes to the boot disk.

Appearance
The environment used the Windows Classic theme up to version 3.0 (based on Windows 7), as it didn't include support for visual styles, although it did at first include some elements such as the newer Aero cursors. The theme service was introduced in WinPE 4.0 (based on Windows 8) together with the Windows Aero theme, although it falls back to Windows Basic window frames due to Desktop Window Manager not being included. Parts of the Aero theme resources were since removed from the Preinstallation Environment as of the original Windows 10 release, leaving behind a variant where the font falls back to Segoe UI Italic in most visual aspects (except the setup application, which has its own font file bundled) and the cursor scheme reverted to the original pre-Vista variation.