Windows Imaging Format
The WIM image format is a file-based disk image format. It was developed by Microsoft for use in its upcoming Windows Vista operating system. WIM files can be managed using the XImage utility that ships with Vista.
Like other disk image formats, a WIM file contains a set of files and associated filesystem information. However, unlike sector-based formats (such as .ISO, .CUE/.BIN used for CD and DVD images), WIM is file based, which means that the smallest unit of information is a file. Advantages include: hardware independance, ability to use heavy compression, unique storage of a file referenced multiple times in the filesystem tree.
The files on the Windows Vista installation DVD which contain the main OS contents to be installed are WIM files.
References
- XImage and WIM Image Format at Microsoft TechNet
- File Extension Details for .WIM at fileext.com