>>12395393
There are unused and unusable spaces for files so that in theory, you should be able to fill them all, you can't because of the sector tips.
Say you have a 33 Kb file - the file system allots it one 32 Kb sector, and puts the remaining 1 Kb in another 32 Kb sector which is then closed off to other data storage. So you have 31 Kb unused and unusable space. Overall, you generally have 5% unused and unusable, but that may vary according to the types and sizes of files - if you have a lot of large videos, you'll have less unused space, but if you have a large number of small image files, you'll have a lot of unused and unusable space.
Look at one of the image files on your puter - right click properties - you'll see size, and size on disk, two different numbers, the size on disk always larger.