Overwrite unused disk space on Windows with Zerofill

Zerofill is a tiny program for Microsoft Windows devices that overwrites the unused disk space of any drive you point it to with zeros.

Designed to improve the compacting of allocated disk space on volumes, something which virtual machine tools or disk compression software benefit from, it makes old data that still sits on those drives unrecoverable as well.

Data that is deleted on PCs is not erased entirely when you hit the delete button or run remove operations. What happens is that Windows removes the reference to files instead but leaves the files on the hard drive.

File recovery software, like Recuva, R-Undelete or may restore deleted files partially or even fully. Whether that is possible or not depends on a single factor: whether the disk space the file occupies has been overwritten with other data since its deletion.

Zerofill

Zerofill is a command line utility developed by the author of FileOptimizer to overwrite free disk space with zeros. It has a size of just 10 Kilobytes and can be run without installation.

Note: the program should not be run on Solid State Drives.

The program runs in DOS environments only which is limiting; an attempt to run the program on a 64-bit Windows 10 system resulted in a not-compatible error.

Zerofill needs to be run with a drive letter as a command parameter, e.g. zerofill d: to fill the free disk space of the d: drive with zeros.

The time it takes to process the drive depends on several factors that include the drive's performance, size and size of free space on the disk.

Zerofill displays a progress bar that visualizes the state of the operation.

Closing Words

The limitation to DOS environments makes Zerofill a specialized software program, one that most Windows users won't run probably or may not even know how to run as they are used to do everything in Windows.

The program works fine when you run it though and it may be used in batch scripts to automate the process.

Alternatives that run on Windows are available, and the majority of Windows users likely prefers them as they run on Windows.

Zerofill is not the first program to offer that functionality. We reviewed programs like SDelete or Eraser before which you may run from within Windows to overwrite unused disk space to prevent restoration.

Now You: do you overwrite free disk space regularly?