Скачать или смотреть How to install Windows 7 into a VHD file? (CMD, Diskpart, Create Vdisk, Select, Attach)

Shift + F10 = Command Prompt
check on which partition there is enough free space to create a VHD file
diskpart
create vdisk file=C:\win7.vhd type=expandable maximum=20480
select vdisk file=C:\win7.vhd
attach vdisk
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By installing Windows 7 (Enterprise or Ultimate) into a virtual hard disk (.vhd file extension) you don't need to create another partition, just store the entire Windows installation and all its files and folders in a single .VHD file.

If you don't want to use this Windows anymore, just delete the .vhd file from ANOTHER Windows installation.

Only Windows 7 or later can be installed into a VHD file, Windows XP, Vista not supported!

It is recommended to defragment your hard disk a little bit more often if you use your Windows in a VHD file.