Hi, I have an iMac that I'm about to list for sale. I want to securely erase the HDD and then reinstall OS X from the restore discs. If I opt for the 7-Pass option (should be enough, there's nothing particularly sensitive on there), how long can I expect the whole procedure to take? Are we measuring in hours or days? The HDD is 500GB in size. Thanks for any help you may be able to offer. Steve.