Microsoft says:
Effectively, you copy the WIM file into a separate “images” partition (just like you would for a recovery image), then use DISM to create pointer files from the standard C: operating system volume into the WIM file. These pointer files are completely transparent, and Windows knows how to boot the operating system (keeping all the files in the WIM) when configured in this setup.
The end result is that a device with 16 GB of storage will be able to keep 12 GB free under Windows 8.1 with a WIMBoot set-up, compared to just 7 GB of free space in the normal method.
Windows 8.1 adds WIMBoot for devices with low storage capacity
Posted on Friday, April 11 2014 @ 9:36 CEST by Thomas De Maesschalck