Windows Imaging Format (WIM) is used for the creation and distribution of disk image files. WIM was first introduced to simplify the deployment of Windows Vista, and it now serves to deploy later versions of Microsoft operating systems.
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With a WIM disk image, a Windows developer can essentially package the contents of a complete hard disk drive -- complete with all of its files and folders -- as a single file. When installed, Windows Setup unpacks that complete disk image to the local computer's hard drive. Large and complex applications can then readily be installed from a single distributable source file.
Computer vendors often use this type of approach to preload a new system with the OS and core applications because it is faster, easier and far less error-prone to copy a single distributable disk image to a new disk rather than take to the time and effort to perform a complete installation. Since WIM files can be bootable, it is a simple matter to launch Windows Setup and start the installation process the very first time a new PC is turned on.
Software developers can use the ImageX tool to create disk images using the WIM format. The tool is provided with the Windows Automated Installation Kit, and Windows Setup for Vista and later relies on the Installation Kit's application programming interface to perform the actual Windows installation. Windows 8 software developers can use Microsoft's Deployment Image Service and Management (DISM) Tool to create WIM files.
WIM is file-based rather than sector-based, allowing a single file package to contain all of the package contents, deduplicate multiple instances of the same components, and also boot and install faster on a wider range of disk hardware. In addition, a single WIM file can contain multiple disk images, allowing users to install some or all of the images depending on what is being distributed. For example, a single WIM file may be created with several different versions of Windows 7. WIM also supports spanning, so large WIM files can be broken into two or more parts denoted with an .SWM extension.