An external hard drive is extremely useful in that it allows the user to back up or store important information separate from the main internal hard drive, which could become compromised by online or offline activities. Sensitive documents, large music files, DVD images, movies, disk images, and even a backup of the contents of your main internal hard drive, can all be kept securely and safely on an external hard drive. When you are online, you can even leave the external drive turned off. Another advantage of an external hard drive is that it is portable and operates on a plug-and-play basis. Any computer with USB or Firewire capability will recognize the external hard drive as a storage device, and assign it a letter to designate it. The drive can then be accessed like a normal internal hard drive. It's a snap to transfer huge files back and forth from work to home, to a friend's house, or between your desktop and laptop. Just plug in the interface cable to quickly reconstruct a working environment, making your favorite programs virtually portable. If you have multiple family members using your computer system, consider an external hard drive to keep financial information and other sensitive documents secure. When you are ready to use the computer, you can plug in the external drive and have all your data and programs available. When finished, simply unplug the drive and take it with you to lock in a drawer or other secure location.