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Windows Imaging File Format (WIM)

This topic introduces the Microsoft Windows Imaging (WIM) file format. WIM is a file-based disk image format that was introduced in Windows Vista. WIM files are compressed packages that contain a number of related files. The format of a WIM file is optimized for maximum compression with LZX, for fast compression with XPRESS, or uncompressed.

For a complete technical description of WIM, see the Windows Imaging File Format (WIM) white paper.

WIM File Structure

A WIM file structure contains up to six types of resources: header, file resource, metadata resource, lookup table, XML data, and integrity table. The following illustration shows the general layout of a WIM file that contains two images.

WIM File Layout

  • WIM Header—Defines the content of the .wim file, including memory location of key resources (metadata resource, lookup table, XML data), and various .wim file attributes (version, size, compression type).
  • File Resources—A series of packages that contain captured data, such as source files.
  • Metadata Resource—Contains information about the files that you are capturing, including directory structure and file attributes. There is one metadata resource for each image in a .wim file.
  • Lookup Table—Contains the memory location of resource files in the .wim file.
  • XML Data—Contains additional data about the image.
  • Integrity Table—Contains security hash information that is used to verify an image’s integrity during an apply operation.