How to delete FREE space of a drive?

[pstein]

How do I tell SDelete GUI to eraser ONLY Free Space?

I miss a context menu for a drive letters similar to "Erase free space with SDelete"

[ricardopolo]

Good Idea, this can be implemented!!

[pstein]

Then keep an eye on the two different types of free spaces:

1.) Free space in a whole unoccupied block/cluster

2.) Free space in the slack space. That means if a file of e.g. 1226 bytes occupies a whole cluster/block with a default size of 4096 bytes then 2870 bytes are free, unsued slackspace.
I am not sure if SDelete can erase this slackspace too. You have to check.