Drive interface: Once youve decided on the speed and capacity you need, you need to consider how the drive will connect to your computer. USB is the most common interface for Macs and PCs, and USB 3.0 delivers a faster data rate than USB 2.0 (5 gbps versus 480 mbps) and more electrical power to an attached device (900mA versus 500mA). The newer standard is backward-compatible, so your computer will be able to use a USB 3.0 drive even if the computer has only USB 2.0 ports.
Thunderbolt ports are twice as fast as USB 3.0 ports, achieving a raw data transfer rate of 10 gbps. Thats speedy enough to transfer a full-length, high-definition movie in less than 30 seconds. Apple provides Thunderbolt ports on its most recent desktop and laptop computers, and the technology is beginning to show up on Windows machines, too. Thunderbolt hard drives are relatively expensive, however: At $180, Buffalos 500GB MiniStation HD-PA500TU3 portable drive costs nearly as much as a 2TB hard drive equipped with a USB 3.0 interface. Still, If you choose to buy one of Buffalos drives, youll be happy to know that the company includes a Thunderbolt cable in the box, given ho pricey these cables are: Apples 2-meter cable costs $49.
FireWire (also known as IEEE 1394) is another high-speed interface used on both Macs and many PCs. The FireWire 400 interface can support a data transfer rate of 400 mbps, while the newer FireWire 800 interface can deliver throughput of 786 mbps.
USB, Thunderbolt, and FireWire all provide enough electrical power to run an attached drive, so the only cord youll need to carry with you is the appropriate interface cable.
Enclosure: The vast majority of portable hard drives are 2.5-inch mechanisms, but not all portable hard drives are the same size. Some models come housed in low-profile enclosures, while others are wrapped in shock-absorbing material within ruggedized cases. Such design decisions affect the drives overall weight, but they also influence how well the drive can survive misadventure. If youre a frequent traveler who grudges every ounce that goes into your laptop bag, youll need to work out for yourself the right balance between data security and tolerable shoulder load.