I know that this post sounds like another attention getting advert but it is true. Windows holds back disk space for the Hibernate feature which a lot of people do not even have enabled on their system
Many people don’t use the windows hibernate at all. Some may not know how to turn it on or even what it is but Windows will still hold back some of your drive space just in case.
What is hibernation?
Hibernation is another way of saving power without having to shutdown your computer properly. When laptops go to sleep they still use a little power however hibernate uses none. When a computer sleeps it stores the state of the machine in RAM and it needs a little power to keep that information. Hibernate stores the information to disk meaning it can turn off completely and still remember everything.
To make sure the system can go into hibernate it reserves some disk space the same size of the RAM. 16GB of RAM = 16GB of Drive space which is a decent chunk on a SSD.
Ensure none of your power profiles use hibernate before turning it off!
Turning it off requires an admin Command Prompt. Right click on Command Prompt and run as admin (Win7 Orb>Accessories>Command Prompt)
Enter the following command:
powercfg -h off
Watch disk space magically appear.