I have been trying to clean out extra content from my 500gb HDD because I was down to 50gb left. After finding little to delete, I starting measuring the file sizes to find out where the space on my hard drive was going. Nothing seemed to add up. I measured all the contents inside my hard drive, and I only had about 330gb used. Why is Windows saying that my drive is almost full when it seems to me that I still have a decent amount of space left?