Does the secure shredder actually do anything? Seems like it only hits disk cache.

I have reason to believe that the Secure Shredder doesn't actually write to the hard disk multiple times, and only hits the disk cache. Mainly because the operation completes very quickly, and the hard disk is active afterwards for a very short time, compared with how long it would take if the data was actually being overwritten multiple times. Since overwriting the disk cache with random patterns is completely pointless, I was wondering if there is any evidence that the shredded files indeed go to the disk each pass or not.

If it turns out that the secure shredder actually works, then all the better, but I'm quite suspicious.