How to boot an WIM image?

Question

Is it possible to boot from a Windows WIM image or is that not possible? What's the difference between ISO and WIM?

Solution

WIM is a multi “image” file format that supports having one of those images declared as “bootable” i.e the typical case of booting a PE environment (boot.wim) contained on MS Windows Install Distributions.

The wim booting process would be something like:

1. The “boot sector" from a particular media is loaded. (MBR on HDD, el Torito on CD/DVD, bootstrap loader on PXE)
2. The "boot sector" passes control to "Bootmgr.exe”
3. "Bootmgr" extracts basic boot information from the "BCD" (Boot Configuration Data)
4. "Bootmgr" opens the WIM
5. "Bootmgr" passes control to "Winload.exe" contained in bootable image of i.e. Boot.wim

ISO and WIM are just different storage file formats with different goals. While the first one is related to the CD/DVD format, the second one is able to hold several images of MS OSs as “snapshots”; I mean as working images of different OSs.

Comments

[VBwhatnow]

en.wikipedia.org/wiki/Windows_Imaging_Format

[Harry Johnston]

Windows PE boots from WIM. In addition to the WIM file you need the Windows boot manager (bootmgr and various associated files). I'm not sure whether or not it is possible to boot a full version of Windows from a WIM file, but I don't think it is supported. (You'd need a lot of memory, since you have to load the image into a ramdisk to boot from it.)

[jiggunjer]

To add to what @HarryJohnston said, PE (or a recovery disk) uses boot.wim. Whereas full images tend to be named install.wim.

[jiggunjer]

An important distinction between ISO and WIM is (respectively) sector based vs file based.

[Hashim Aziz]

What does PE environment mean here? Is it talking about the Preinstallation Environment or something else?

[Pat]

Yes; the environment created when booting a "Windows PE" WIM file like Boot.wim.