External Hard Drives

External hard drives are versatile and useful, especially for freelance professionals and technicians who may need to have data from their home PC readily available with them wherever they go. External hard drives are also useful backup solutions. Some of these drives can hold hundreds of gigabytes of information, far more than any CD or DVD can. Most external hard drives function with both Macs and PCs making them a convenient cross-OS data transfer option. If you have deep storage and portability needs, an external hard drive might suit your needs. This guide will help you decide what kind of hard drive is best for you and give you a basic understanding of the differences between particular specifications.

Things to Keep In Mind

Purchasing an external hard drive, while hardly an impulse buy, requires a little less serious investigation than purchasing an aircraft carrier.

Interface

External hard drives come with one of four types of interfaces. However, today's models are generally split between USB/FireWire combinations and External SATA.

• USB or FireWire: Most Macs and PCs have some form of USB or FireWire  ports (FireWire is a.k.a. IEEE 1394). Plugging these external hard drives in is as easy as plugging in a video game controller or a camera. The downside of USB and Firewire is that transfer speeds are usually not as good as your internal hard drive, which isn't a particularly huge deal in most circumstances. However, if you're computer suddenly catches fire and you need to transfer your manuscripts in a hurry, it could be a problem. Be aware that both USB and FireWire offer high and low speed variations, so be on the look out for USB 2.0 versus 1.1 and FireWire 800 versus 400. Older computers may have trouble with the newer, faster formats but most USB 2.0 and FireWire 800 devices can connect at the slower speed if necessary.
• External SATA: External Serial Advanced Technology Attachments  offer the faster transfer speeds on the external hard drive market today. However, models using this technology are less common and more expensive. Laptops will generally require an adaptor to use this option.
• PC Card (PCMCIA): Previously appreciated for its form factor, this aging format now appears to be on the decline due to seemingly having reached capacity in storage and transfer rates. Most that manage to fit inside laptop computers are limited to Toshiba's 5 GB card , but one company manufactures PCMCIA external drives  that stick out while using the interface to reach 160 GB.

Spindle Speed

Spindle speed is measured in revolution per minute. Generally, the more RPMs you're hard drive has, the better it will perform.  Most spindle speeds are between 3,000 RPMs and 10,000 RPMs.

Physical Size and Capacity

Quite logically, the bigger your external hard drive is, the more space it's probably going to have.  Models that are less than an inch big will probably fit no more than 15GB of information, while 3.5 inch models can fit upwards of 1,000 gigabytes (i.e. 1 terabyte).  Unfortunately, those two inches can make be the difference between a 6oz device and 6lb device.

RAID Compatiblity

Some external hard drives offer RAID compatiblity, which allows for the device to function as part of a single virtual hard drive.

Cache

Cache refers to the amount of on-board memory included in the external hard drive. Cache provides a memory buffer when transfering to and from a PC. More memory means faster transfers.

Highly Rated External Hard Drives

Top Five External Hard Drives According to PC World
Maxtor OneTouch III	Apricorn EZ Bus DTS SATA	CMS 400GB Velocity Automatic Backup System	WiebeTech SilverSATA II	Iomega 400GB Triple Interface
This $800 device features 1000GB of storage, perfect for those with large external backup needs. It's also RAID-compatible.	This hard drive features 250GB of storage space for under $200. One of the fatest, best performing and affordable drives available.	This 400GB drive was the first Windows bootable external backup system available. The CMS Velocity Automatic uses an SATA interface.	The WiebeTech SilverSATA II offers 100GB of space. The SilverSATA wiill give you incredible transfer speeds, but it'll cost you up to $1300.	Featuring 400GB and a USB interface. It also loads of free sofware. The cost is about $350, which equals about $0.88 per gigabyte.