TreeSize facilitates the search for hidden disk space such as content attached as Alternate Data Streams, which are invisible to most other programs.
Alternate Data Streams are a modern but scarcely used feature of NTFS. It permits applications to save additional streams in files, for example, to store metadata.
Those streams, however, do not influence the file size value shown in the Windows Explorer and most other tools. This way, a 4GB movie could be stored in an 1KB text document. TreeSize is abler to show the size of the Alternate Data Streams in an optional column and adds the to the Allocated Space of a file. Using TreeSize to search for files, you can selectively search for files with alternate data streams.
Right click on the column header to enable the column the the Alternate Data Streams (ADS). Since the determination of ADS sizes takes up additional time, the feature to track NTFS specific features first needs to be switched on in the "Options" dialog.