Hard drive enclosures take an internal hard drive and turn it into an external hard drive. This is useful if you want some extra space inside your computer, or if you need access to your laptop's hard drive from your desktop. Creating an external drive using an enclosure also provides increased flexibility. You choose the hard drive and the enclosure. This lets you decide if the drive has a fan for cooling or a quieter metal dissipation system. You retain control over the type of cable used to connect to the computer and whether the drive requires a power adapter or is portable and uses USB power.
