.WIM Files

A .wim file (Windows Imaging Format) is a file-based disk image format developed by Microsoft. A file-based disk image format differs from sector-based formats by using a file as the fundamental unit of information.

The primary advantages of being file-based is the hardware independence and single-instance storage of a file referenced multiple times in the filesystem tree (de-duplication).  Since files are stored inside a single .wim file, the overhead of opening and closing many individual files is reduced.  The cost of reading or writing many thousands of individual files on the local disk is negated by hardware and software-based disk caching as well as sequential reading and writing of the data.

.WIM files can contain multiple disk images, which are referenced either by their numerical index or by their unique name.  Due to the use of single-instance storage, the more each successive disk image has in common with previous images added to the WIM file, the less new data will be added. A WIM can also be split (spanned) into multiple parts, which have the .swm extension.

One WIM file can address different hardware configurations as there is no requirement as in a sector-by-sector copy installs that the destination hardware match the source hardware.

WIM can store multiple images within a single file as described above in the install.wim of the base operating system; the same can be done for custom *.wim files created by system admins.

When you store multiple images within a single file you can do this as just part of a core build for desktop deployments or with the use of Catalog (CLG) files that allow for the option to set up multiple applications to be deployed as part of the operating system build.

You can service the WIM image offline from its stored location and add or remove certain operating system components, files, updates, and drivers without creating a new image.

Windows Imaging format has the flexibility to install a disk image on partitions of any size. Sector-by-sector images require deployments of an image to a partition that is the same size or larger than the source disk.

WIMGAPI is the Windows Imaging API that developers can use to manage WIM image files.

WIM deployments can be performed nondestructively. Data can be on the existing volume and the image can be deployed without erasing the existing contents of the volume.