Windows Imaging Format
| Filename extension | .wim .swm |
|---|---|
| Magic number | MSWIM |
| Developed by | Microsoft |
| Type of format | Disk image |
The Windows Imaging Format (WIM) is a file-based disk image format. It was developed by Microsoft to help deploy Windows Vista and subsequent versions of Windows operating system family, as well as Windows Fundamentals for Legacy PCs.
Like other disk image formats, a WIM file contains a set of files and associated filesystem metadata. However, unlike sector-based formats (such as ISO or VHD), WIM is file-based: The fundamental unit of information in a WIM is a file.
The primary advantages of being file-based is hardware independence and single-instance storage of a file referenced multiple times in the filesystem tree. Since the 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.
WIM images can be made bootable. Windows boot loader supports booting Windows from within a WIM file. Windows Setup DVD in Windows Vista and later use such WIM files. In this case, BOOT.WIM contains a bootable version of Windows PE from which the installation is performed. Other setup files are held in the INSTALL.WIM.
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