G'Day elloko,
The NTFS file system is a bit like a set of storage boxes -
each of 4kB in size. When a file is stored it is allocated a
whole number of boxes, even though the last box may be
almost empty.
When you look at properties, you see the total number
of boxes allocated, which includes the empty space in
all the "last boxes" (this empty space is no longer available
and cannot be used).
When you select all files, you see the total size of the data
in the files, which does NOT include the empty space(s).
The file system is very efficient at storing large files, but a
huge amount of space is wasted with large numbers of
very small files.
All file systems on modern computer systems suffer from
this problem.
If you can identify certain folders that contain small files then
one solution is to allow compression in those folders so that
they becomes a bit like Zip files. However there can be severe
performance issues since processor and disk access time are
spent zipping and unzipping files as they are accessed, modified
and saved.
