- Essentially, there are two types of hard drives: those for laptops and those for desktop computers. Laptop hard drives are 2 1/2 inches long and desktop drives are 3 1/2 inches long. Both types can be installed into enclosures that make them stand-alone external hard drives, thus giving the user extra storage space without having to change the hard drive inside the computer.
- Hard drive enclosures are essentially metal or plastic boxes that contain a power supply and computer connections. They have plugs that connect to a power cord that usually contains the conversion box---often called "the brick"---that transforms alternating current to direct current for use of the hard drive. Some enclosures have the power converter inside, but this is rare. The enclosure also has a cradle on which the hard drive is seated and a ribbon cable that connects to universal standard bus (USB) or FireWire ports. Some enclosures allow connection via both.
- Hard drives from laptop or desktop computers can be seated in enclosures. Their pins connect to a ribbon cable that in turn connects to the USB or FireWire ports. Whereas the internal hard drive is powered by the computer itself, the external hard drive in an enclosure must be powered from another source. Some smaller enclosures allow the drives to be powered via the USB cable without the need for an AC converter. Data is transferred between the external hard drive and the computer via the USB or FireWire cable. Enclosures usually have indicator lights that tell the user when it is powered up and when it is being accessed. USB and FireWire external hard drives in enclosures are "hot pluggable," meaning you can plug them in or unplug them from a computer while it is powered on without hurting data or hardware.
