Windows PE was created to help OEMs and IT professionals boot a computer with no functioning operating system.

In the past, OEMs and IT professionals often used an MS-DOS-based boot floppy disk to start a computer. However, an MS-DOS-based boot floppy disk has a number of limitations that make it difficult to use for pre-installing Windows or recovering existing installations or data. It has:

• No support for the NTFS file system.
  
  
• No native networking support.
  
  
• No support for 32-bit (or 64-bit) Windows device drivers, making it necessary to locate 16-bit drivers.
  
  
• Limited support for custom applications and scripts.
  
  

The limitations of MS-DOS-based startup disks led Microsoft to develop Windows PE, which is now the primary Microsoft tool for booting computers with no functioning operating system. Once you boot a computer into Windows PE, you can prepare it for Windows installation, and then initiate Windows Setup from a network or local source. You can also service an existing copy of Windows or recover data.

Because Windows PE is based on the kernel for Windows 7, it overcomes the limitations of MS-DOS-based boot disks by providing the following capabilities:

• Native support for the NTFS 5.x file system, including dynamic volume creation and management.
  
  
• Native support for TCP/IP networking and file sharing (client only).
  
  
• Native support for 32-bit (or 64-bit) Windows device drivers.
  
  
• Native support for a subset of the Win32 Application Programming Interface (API).
  
  
• Optional support for Windows Management Instrumentation (WMI), Microsoft Data Access Component (MDAC) and HTML Application (HTA).
  
  
• Ability to start from a number of media types, including CD, DVD, USB flash drive (UFD), and a Remote Installation Services (RIS) server.
  
  
• Windows PE offline sessions are supported.
  
  
• Windows PE images can be serviced offline.
  
  
• Windows PE includes all Hyper-V™ drivers except display drivers. This enables Windows PE to run in Hypervisor. Supported features include mass storage, mouse integration, and network adapters.
  
  

	Note:
	This section discusses standalone Windows PE. Customized versions of Windows PE used in other products and technologies such as Windows Deployment Services may provide different functionality. For more information about using Windows PE in these environments, consult the relevant product documentation.

Windows PE is a modified version of the Windows operating system that is designed to support installing Windows and troubleshooting and recovering an installation that can no longer boot.

• Installing Windows 7. Windows PE runs every time you install Windows 7. The graphical tools that collect configuration information during the Setup phase are running within Windows PE. In addition, information technology (IT) departments can customize and extend Windows PE to meet their unique deployment needs. Windows PE also provides support for servicing Windows images.
  
  

  	Important:
  	Windows PE supports the deployment of previous versions of Windows. Refer to your Microsoft Software License Terms for restrictions, or contact your Microsoft representative.

• Troubleshooting. Windows PE is useful for both automatic and manual troubleshooting. For example, if Windows 7 fails to start because of a corrupted system file, Windows PE can automatically start and launch the Windows Recovery Environment (Windows RE). You can also manually start Windows PE to use built-in or customized troubleshooting and diagnostic tools.
  
  
• Recovery. OEMs and independent software vendors (ISVs) can use Windows PE to build customized, automated solutions for recovering and rebuilding computers running Windows 7. For example, users can start their computers from Windows PE recovery CDs or recovery partitions to automatically reformat their hard disks and to reinstall Windows 7 with the original drivers, settings, and applications.
  
  

Windows PE is a subset of Windows 7, and has the following limitations:

• To reduce its size, Windows PE includes only a subset of the available Win32 APIs. I/O (disk and network) and core Win32 APIs are included.
  
  
• To prevent its use as a pirated operating system, Windows PE automatically stops running the shell and reboots after 72 hours of continuous use. This time period is not configurable.
  
  
• Windows PE cannot act as a file server or Terminal Server. (Remote Desktop is unsupported.)
  
  
• Distributed File System (DFS) name resolution is supported for standalone roots only. Domain roots are not supported. Standalone DFS roots allow for a DFS root that exists only on the local computer, and thus does not use Active Directory®.
  
  
• The supported methods of connecting to file servers are TCP/IP and NetBIOS over TCP/IP. Other methods, such as the IPX/SPX network protocol, are not supported.
  
  
• All changes that you make to the Windows PE registry while running Windows PE are lost the next time you restart the computer. To make permanent registry changes, you must edit the registry offline before starting Windows PE.
  
  
• Drive letters are assigned in consecutive order as you create partitions in Windows PE. However, the driver letters are reset to the default order when you restart Windows PE.
  
  
• Windows PE does not support the Microsoft .NET framework or the Common Language Runtime (CLR).
  
  
• Windows PE does not include Windows on Windows 32 (WOW32), Windows on Windows 64 (WOW64), Virtual DOS Machine (VDM), OS/2, or POSIX subsystems.
  
  
• Windows PE can be used to configure and to partition a computer's disks before starting Windows Setup. If any hard disks are converted to dynamic disks with Diskpart.exe before you start Windows Setup, then those hard disks are recognized as foreign when the operating system is installed, and any volumes on those hard disks will not be accessible.
  
  
• Windows PE does not support applications packaged with Windows® Installer (.msi).
  
  
• Windows PE does not support 802.1x.
  
  
• Windows PE does not support booting from a target path that contains non-English characters.
  
  

Windows PE relies on a number of Windows technologies to function properly.

• If you use Windows PE on a network, Dynamic Host Configuration Protocol (DHCP) and Domain Name Services (DNS) servers are useful but not required.
  
  
• If you boot Windows PE from a network, you must use Windows Deployment Services.
  
  
• If you install Windows, you must run Windows Setup (Setup.exe in Windows 7 or Winnt32.exe for Windows Server 2003).
  
  
• If you automate a Windows 7 installation, you must use an Unattend.xml answer file.
  
  

Windows PE is closely related to a number of other Windows installation technologies, as well as several recovery technologies. Some of these technologies, such as Windows DS and Setup for Windows 7, include customized versions of Windows PE.

Windows Setup

Unattended Setup

• How Windows PE Works
• Windows PE Tools