This question already has an answer here:
Consider following 2 disk wipe procedures, using only vanilla Windows installation:
First do a quick-format to make the disk appear empty, then do one of these:
Just do full format of the disk.
Bitlocker-encrypt the entire drive (all space) using a strong key which is then thrown away, leaving disk unusable until formatted.
Both are operations which can be started quickly and then left running unattended, and then the drive yanked out when it's finished. And the concern is wiping the the data that was on the disk previously.
Is doing 2 more secure than doing just 1? Or to put it other way, who can recover the original contents after alternative 1, and who can recover them after alternative 2?
So, the key point of this question is: is there any advantage of writing single pass of "random" data (by encrypting) instead of writing a single pass of zeros (by full format).
Bonus question: Can you suggest other alternatives for Windows 7 or 8, assuming no extra software can be installed?