Afraid to shred "unused space" with eraser

I've used this feature on my secondary drives, but i monitored it closely and I'm pretty sure Eraser filled the entire (or almost) drive to shred the free space (I guess that's how it works).

If I use it on my primary drive, with Windows running, won't Eraser crash it? I mean, once I filled my C: drive and it wasn't pretty.

Or does it prevent it from happening?

Sorry if this is a dumb question.
=)

 

Eraser should't ceash the OS, it creates a file or a set of files and fils them with rundom data till the HDD is full than it erases them.
Windows should be fine with this.

 

Eraser will erase the files it makes at the very end of the freespace wipe cycle so don't panic and stop Erasers cycle. I do my freespace wipe at night when I sleep.

 

You actually sleep?