Windows 7 / Getting Started

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Understanding Windows pe

Windows 7 and Windows Server 2008 Release 2 use Windows PE 3.0. Windows PE 3.0 is a bootable startup environment that provides operating system features for the following:

• Installation When you install Windows 7, the graphical tools that collect system information during the setup phase are running within Windows PE.
• Deployment When a new computer performs a network boot, the builtin Preboot Execution Environment (PXE) client can connect to a Windows Deployment Services server, download a Windows PE image across the network, and then run deployment scripts within this environment.
• Recovery Windows PE enables you to access and run the Startup Repair tool if Windows 7 fails to start because of a corrupted system file.
• Troubleshooting You can manually start Windows PE to perform troubleshooting or diagnostics testing if Windows 7 is experiencing problems that can't otherwise be diagnosed.

Windows PE is modular and extensible, and it provides full access to partitions formatted using the file allocation table (FAT) or NTFS file system. Because Windows PE is built from a subset of Windows components, you can run many Windows applications, work with hardware devices, and communicate across Internet Protocol (IP) networks. Several command-line tools are available in Windows PE, including:

• BCDBoot A tool that initializes the boot configuration data (BCD) store and allows you to copy boot environment files to the system partition
• Bootsect A tool for creating and working with boot sectors on hard disks and flash drives
• Diskpart A tool for creating and working with disks, partitions, and volumes
• DISM An advanced tool for servicing and maintaining images
• Drvload A support tool for adding device drivers and dynamically loading a driver after Windows PE has started
• ImageX A tool for capturing and applying Windows images
• Net A set of support commands that enables you to manage local users, start and stop services, and connect to shared folders
• Netcfg A tool that configures network access
• Oscdimg A tool for creating CD and DVD ISO image files
• Wpeinit A tool that initializes Windows PE every time it boots

For deployment, you can execute these tools from configuration scripts to perform key configuration tasks. As examples, you can:

• Use Netcfg to configure network access.
• Use Drvload to install a driver and use the hardware without restarting the computer.
• Run DiskPart to partition and format the computer's hard disk.
• Use Net Share to connect to a shared folder containing the Windows 7 Setup files.
• Run the Windows 7 Setup program to install the operating system.

You can get the Windows PE build environment in the Windows OEM Preinstallation Kit (Windows OPK), the Windows Automated Installation Kit (Windows AIK), or the Windows PE Kit. To use Windows PE to create boot and installation environments for Windows 7, you must use the version of these kits for Windows 7. Because these kits are often updated, look for the one for the service pack you are currently using.

Included in these kits are separate 32-bit and 64-bit editions of Windows PE. You use the 32-bit edition to prepare 32-bit versions of Windows 7. You use the 64-bit edition to prepare 64-bit versions of Windows 7.

As with Windows 7 itself, Windows PE can be contained within a disk image. When you store a Windows 7 image in a disk image, the only way to start Windows 7 is to copy the full image to the computer's hard disk. When you store Windows PE in a disk image, however, you can start Windows PE from the image without having to copy it to the computer's hard disk. This enables you to store Windows PE disk images on bootable media, such as a DVD or USB flash drive, and then start Windows PE directly from that media. The Windows 7 distribution media uses this technique to load Windows PE into RAM during setup of the operating system.

You can load Windows PE into RAM as well, which might be necessary for troubleshooting. When you do this, the Windows PE boot loader creates a virtual RAM disk in memory and then copies a compressed version of Windows PE to the RAM disk. Afterward, the boot loader mounts the RAM disk as if it were a disk drive and starts Windows PE. Running Windows PE from RAM enables you to write temporary files to the virtual RAM disk, which isn't possible when running from read-only media such as a CD. It also enables you to remove the Windows PE media after Windows PE has started and then insert different media into the computer's CD-ROM or DVD-ROM drive or USB flash drive.

When working with Windows PE, keep the following in mind:

• Windows PE requires a computer with a VESA-compatible display and a minimum of 256 megabytes (MB) of RAM. During startup, if Windows PE can't detect the video settings, it uses a screen resolution of 640 x 480 pixels. Otherwise, it uses the highest resolution possible.
• Windows PE supports Plug and Play (PnP) devices. Hardware devices can be detected and installed while Windows PE is running. This means that you can install any PnP device that has a driver in the driver store, including removable media and hard disk devices.
• Windows PE supports both IPv4 and IPv6. Although you can access shared folders on other computers from Windows PE, other computers cannot access files or folders on a computer running Windows PE.
• Windows PE always starts with the default drive letter assignments. This means that drive letter assignments aren't persistent between sessions.
• Windows PE discards online changes to the registry. This means changes to the registry aren't persistent between sessions. To make permanent changes to the registry, you must mount the Windows PE image and make changes using the Registry editor.
• Windows PE doesn't support the Microsoft .NET Framework or Windows on Windows 64 (WOW64) subsystem. This means you cannot use .NET applications on any version of Windows PE, 16-bit applications on 32-bit versions of Windows PE, or 32-bit applications on 64-bit versions of Windows PE.
• Windows PE automatically restarts after running for 72 hours. This behavior is a safeguard to prevent Windows PE from being used as a general-purpose operating system.

You can boot Windows PE from the Boot.wim file on the Windows distribution media. When Windows PE initializes, the Wpeinit command is called to initialize PnP devices and start the network connection.