Simply adding up the folder sizes does not include the items on the desktop, nor invisible files.
For example, using a utility called Find Pro III to locate hidden files, 144 of them were found. 137 of them were named "Icon". These files are created when you paste an icon on a folder. If you create an empty folder and paste an icon on it, the "Get Info" window shows that the folder contains zero╩K and no items. However, if you throw this folder in the trash and "Get Info" on the trash, the window shows one file and one folder in the trash and the size of the file is greater than zero K. Therefore, the Finder apparently does not count invisible files when it calculates the size of a folder.
To summarize, the displaying of folder sizes is not always accurate due to the invisible files, which the Finder ignores, and the virtual memory swap file, which is whatever size is set in the Memory control panel. Also, items on the Desktop are not shown as being in any folder but they take up space and are included in total disk usage. By adding up all of the space these items take on the drive, the total amount of disk space used should be very close to the amount of space the disk info shows.
Article Change History:
15 Dec 1994 - Added keyword and made minor technical updates.
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