I am having trouble installing my Windows 8.1 64-bit installation disk I purchased for $80.00, due to my external disk drive not working properly (I don't have any internal optical drives.) After looking around, I found a free Windows 8.1 64-bit Enterprise ISO installation download provided my Microsoft, which can be formatted on a bootable USB drive. I would just like to know the difference between the disk I purchased compared to the free installation download, and whether I should just get the free version. Thanks!