It isn't surprising to see a large size difference between the hard
drive itself and the total folders on the hard drive. Here are
factors that explain the difference:
* The invisible files (such as AppleShare PDS, Desktop DB, Desktop DF,
and Desktop Folder) aren't counted in Get Info size for folders.
* The size shown in the Get Info box for folders is the actual file
size, which includes data and resource forks. For example, a text
file which contains only 30 bytes, showed Size: 3K on disk (480
bytes used); 480 bytes (30 bytes for data, 450 bytes for resource)
will be added to the folder Get Info size, and 3K will be added to
the hard drive Get Info size.
Since the hard disk is a block device, any file created must reside
on the block factor boundary -- 3K, in this case, is the size that
the disk drive allocates for this file. This accounts for a lot of
differences, especially if you have a lot of small files on the
drive.