Now Windows 8.1 Update 1 can be installed with smaller disks, e.g. devices with 16GB or 32GB SSDs or eMMC storage, while still ensuring that there is plenty of storage left for apps and data.Microsoft has introduced a new deployment option, called Windows Image Boot (or WIMBoot).All the individual Windows files from an image (WIM) file, they remain compressed in the WIM.
On HDD partition it looks like this:
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