Fully erasing a hard drive without removing the OS

[CoW]8(0)]

I'm returning a computer for repair and I need to remove all my personal data on it. I am going to use the restore partition to restore the computer back to its original state but I know that my old files can still be restored if the space they occupied isn't overwritten.

Are there any programs than can overwrite all the free space on the machine so my files can't be restored?

 

[dotCapone]

I'm pretty sure the newest version of CCleaner can do that.

 

[drescherjm]

Do you have a recovery partition on the machine?

 

[drescherjm]

I'm pretty sure the newest version of CCleaner can do that.

These can do their job but I believe you need to make sure you delete all of your files first. Then clean freespace.

 

[Netwerkz101]

SysInternals SDelete

I should have added that this is for file delete and you would use it
in place of a partition nuke (the non-recovery partition(s) of course)

 

[CoW]8(0)]

Thanks for the suggestions, I've been using sfill in linux for the time being.