Windows Vista Varying free storage?

[WinFreak]

In 2013, our Vista SP2 Business PC (that OS was pre-installed, and actually great. In our experience, Vista worked as great as Windows 7) with 1 TB HDD had 610 GB free. Suddenly, after a few days, 627 GB were free, then 598 GB, without doing much. Then back to 618 GB free.

Not that I mind it, but what did possibly cause the storage to get 17 GB free, then 29 GB filled, then 20 GB less?

 

[patcooke]

Many background resources will contribute to such manor variations ( on a 1TB drive 20GB is approx 2% of the drive) Such variable usage includes the pagefile and swapfile (temporary usage of hard drive to temporarily accommodate constantly varying RAM images) and virtual memory.

 

[Neemobeer]

VSS, hibernation and page files, temporary windows update cache to name a few items that will change size