Users increasingly rely on external hard drives as back up devices connected directly to their systems using USB or Firewire interfaces.
Don’t think it won’t happen to you;
If your desktop or laptop hard drive stopped working right now, do you have a current copy of all of your files kept somewhere else?
There are essentially two main physical sizes which are used for Desktop use or Laptops (mobiles).
Typical products (as seen below) are available from Lacie or Western Digital