Generally, each directory in the directory list has a pseudo subdirectory <Files>. There, all ordinary files of the directory are put together. That is, all files, which are immediate children of the directory, not those of subdirectories. This has the advantage, that the directory list is cleaner and that the statistics is sounder. Because with this item you can see how much space is used all in all by the files of the directory (not of subdirectories).
The <Files> item is omitted, if there is only one file in the directory, or if it has no subdirectories.
If you have activated "Show Free Space" in the Options menu, each drive has an <Free Space> item. The size of this item tallies with the amount of free space available on the drive. In the treemap this item has a dark grey color. Through the <Free Space> item you get an impression of the ratio between the totally used disk space and the free disk space. This information corresponds with the value shown in the Windows Explorer properties dialog for the drive.
If you have activated "Show Unknown" in the Options menu, each drive has an <Unknown> item. The matter is as follows. On the one hand, WinDirStat knows the total capacity of the drive and the free disk space. (These values tally with the number shown by the Windows Explorer properties dialog for the drive.) On the other hand WinDirStat has determined the sizes of all files and added them up. Well, <Unknown> is the difference: Total capacity minus free space minus determined sum. This rest can be greater than zero by serveral reasons. For instance there can be directories (e.g. "System Volume Information") with read-access denied. Their size cannot be included in the sum calculated by WinDirStat. In the treemap, the <Unknown> item is colored vivid yellow.
< (in column headings)
indicates that the list is sorted by this column in ascending order.
> (in column headings)
indicates that the list is sorted by this column in descending order.