This is something I didn't expect, but the PlayStation 4 will not support external storage devices. This means that the internal 500GB mechanical HDD is all you'll be able to use.
However, you can upgrade the internal drive, as long as it's over 160GB in size. But, backups of your PS4 will not be capable because the next-gen console does not support external HDDs. I'm hoping that Sony reverses on this decision, and quick, because I'm sure it's going to have people worried not just now, but when they attempt to install an external drive to the PS4.
Really, in 2013 going into 2014 with a "next-generation" console, external storage should just be a given. Please Sony, wake up to this nonsense. Games are getting bigger, with 40GB+ installations and you want to stop people from using external storage... really?