Does Windows 10's "reset PC and clean the drive" correctly clean the drive?

Solution 1:

When you choose reset your PC you will have the options to "Fully clean the drive" or "Just remove my files". By picking "Fully clean my drive" it will take several hours and it will attempt to overwrite anything on the drive with zeroes, so yes it will. You have to remember there are some companies capable of restoring data from your disk but this will make it a lot harder than a quick format.

If you choose "Just remove my files" it will just do a quick format.

Description from Microsoft:

The behavior of this option will vary depending on if the drive is encrypted with BitLocker.

If the volume is not encrypted, then this option performs a full format of the disk and writes zeroes to every sector. This will take quite a long time. This is similar to running the command below:

format.exe c:\ /P:0

If the volume is encrypted with BitLocker, only a quick format is performed, as that wipes all of the information necessary to decrypt the disk. With no way to decrypt the disk, the data is effectively lost.

Note that this procedure will take much longer than the quick format. It could take hours on a large hard drive. This is not something that you would want to do live with a customer. It would be better to start it and arrange a follow-up later.

Source: http://blogs.msdn.com/b/olivnie/archive/2013/04/05/recovery-and-troubleshooting.aspx