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<Unknown>
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.

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