How to Erase Unused Hard Drive Sectors

Even when you delete a file and empty the Recycle Bin, files are still recoverable by using specialized recovery software. If you fear deleted files could resurface after deletion, thoroughly erasing unused sectors will overwrite the deleted files to prevent their recovery. Microsoft offers a small SDelete utility that enables you to overwrite unused sectors using the Command Prompt. However, make sure deleted files are emptied from the Recycle Bin, or the sectors in which the files reside will not be considered unused.

Download "SDelete" from Microsoft (see link in Resources). The executable is provided in a ZIP-compressed file, so you'll need to extract the file.

Press "Win-E" to open File Explorer, double-click the "SDelete.zip" file to open it and drag-and-drop the "SDelete.exe" file into the "C:/Windows/System32/" folder. Alternatively, select the "SDelete.exe" file, press "Ctrl-C," navigate to the "C:/Windows/System32/" folder and press "Ctrl-V" to copy it. If you get a security warning, click "Continue."

Press "Win-X" to open the Windows 8.1 Utilities menu and select "Command Prompt."

Type "sdelete -z c:" and press "Enter" to write zeros to all unused sectors in the Windows "C" partition. Alternatively, type "sdelete -c c:" to similarly clean unused space, but using the "-z" command offers greater security by overwriting files with random data. To specify a different hard drive partition, replace "c:" with the drive letter of the partition, followed by a colon.