Storage size problem

[kid_wonder24]

I'm unzipping some files the other day and windows shows a popup stating I am low on disk space, with only 6GB left on my 120GB drive. This drive is strictly storage, and I was confused since I didn't think it was very close to being full. After adding up the file sizes on the drive, I can only find 90GB of data, and I can't figure out what's happened to the other 21GB (It only registers as a 111GB). Any thoughts on this?

 

[kid_wonder24]

....Apparently not