External Hard Disks

The vast majority of hard disks are internal, which means they are designed to be mounted inside a PC, and hidden from the user. This is why they have a rather "rough" outside appearance, with the logic board exposed, etc. (For some reason I always liked the way internal drives looked... maybe just because I'm such a storage freak). The fact that they are intended to be installed internally is also the reason why they come in standardized form factors--so they will fit inside the PC case in predictable ways.

External hard drives are a big market -- the hard drives themselves are the same, however they are merely mounted in an external enclosure for protection and aesthetics. The enclosure has connections for power and data transfer to/from the computer.

There are two types of external hard drives: portable and standard. Portable external hard drives are pocket-sized and have a 2.5" notebook hard drive inside. Often they can be powered by a USB connection so an external power adapter is not necessary. Standard external drives are larger and house a 3.5" desktop hard drive; they require much more power than 2.5" drives and require an AC adapter.

External hard drives connect to the computer in a number of ways; the most common is via USB. The current USB 2.0 standard is somewhat slow (capped at about 30MB/s transfer rate), however the emerging USB 3.0 standard has a transfer rate higher than that of any hard disk's. Another common interface is external SATA, or e-SATA; it is exactly as the name implies, an external SATA connection. FireWire 400 and 800 is the another type of connector, however is not nearly as common; FireWire never really took off compared to USB (even though it was arguably better for data transfers). Lastly, some external hard drives come with an Ethernet connection so they can be connected to a router and serve as a network drive.

Most external hard drives are sold pre-packaged -- that is, they include the enclosure and the hard disk. However, many stores simply sell the enclosure and allow you to put your own drive in. This is a great way to reuse old drives or simply use whatever hard disk you want. Assembly is usually just a matter of inserting the hard drive and screwing or snapping the enclosure shut. Often, DIY enclosures are of better quality than the pre-packaged drives.

Next: Removable Hard Disk Trays