But when it comes to portability and smaller-capacity storage, USB thumb drives prevail. These flash memory devices connect easily, remove quickly, and are simple to use. See our companion report on USB flash drives if you need to store less than 4GB of data. Current USB drives top out at about 8GB, and mainstream models reach 4GB.
Multimedia files – especially uncompressed video files – can take up a lot of hard drive space on a computer, and many users quickly exceed the space on their internal hard drive. An external drive is an easy way to increase hard-drive space without installing a new internal hard drive. An external drive can also be used as a backup drive in case your computer's drive becomes corrupted or unstable. Reviewers uniformly recommend that users back up their computers – or at least their most important files – at least once a week. Backing up data to multiple CDs or DVDs can be cumbersome, often requiring several discs, but an external hard drive can hold much more data. Backup software makes performing this task virtually automatic.
In general, test reports measure actual capacity against manufacturers' claims, disc speed (also called spindle speed), external data transfer rate and connectivity (USB, FireWire, eSATA). They also examine ease of use, software and physical design features, such as whether the drive sits vertically or horizontally.
Ease of use is another important consideration. Reviewers concur that backup software makes a difference in the utility of these drives. Nearly all external hard drives come with software to help schedule backups and move files, and new features include system rollback capability, as well as security options that keep your drive safe from sudden disconnects, shutdowns and virus invasions (an occupational hazard for drives that are switched among multiple systems). Keep in mind there's no need to use the manufacturer's supplied software with an external hard drive. Most allow you to drag and drop files, bypassing software entirely. If you want to perform scheduled backups, there are also many effective third-party software solutions available.
Types of external hard drives
External hard drives come in two main form factors. The highest-capacity hard drives can be about the size of a hardcover book, with capacities from about 300GB to 1,000GB (also known as a terabyte). These high capacity drives aren't portable -- they're meant to be parked on your desk. They rely on an AC brick for power.
Portable external hard drives are about the size of a paperback, and the smallest models are about the size of a deck of cards. These smaller drives usually connect with a USB or FireWire cable and most come in capacities of 40GB to 160GB. They are small enough that they can pull all the power they need through the USB or FireWire port, so you don't need an external power supply. The third main form factor are tiny USB thumb drives which come in capacities up to 8GB, and these are covered in our report on USB flash drives.
Reviews say you shouldn't consider an external hard drive of less than 40GB, and most recommend buying as much storage as you can realistically afford. Consumer Reports magazine recommends a size of 200GB to 300GB for most families. Laptop users who want a more portable drive will need to settle for less.
Disk speed, also called spindle speed, refers to the disk’s rotational speed, which partly determines the speed of data transfer. Reviews say 5,400rpm is the lowest disk speed you should consider. Portable hard drives generally run at this speed, which matches that of most laptop hard drives. A speed of 7,200rpm tends to be the most common for larger external hard drives, and 10,000rpm drives are slowly becoming more commonplace.
Buffer size represents the amount of cached, or stored memory your drive can handle while waiting for the next request from the system. Clearly, the bigger the buffer, the more data it can hold and the more quickly it can deliver that data. Budget external hard drives tend to have a 2MB buffer, although 8MB is common too. Opt for the latter if you can, as it can make a noticeable difference. A few of the latest drives have 16MB buffers.
Important Features: External hard drives
Choose an external drive based on your source system, operating system and backup needs. If you mainly plan to store or backup data files, you don't need the fastest external hard drive. Those who plan to back up multimedia files need more storage capacity and faster transfer speeds.If you want an eSATA drive, you'll need an adapter for your computer.
Look for preloaded easy-to-use backup capabilities. Whichever external drive you choose, you'll want software that makes backups easy so that you backup often. Some models build this into the hardware design by providing one button backup capability.
If your storage needs are modest, consider a USB flash drive instead. Because it's solid state and doesn't have the mechanical vulnerabilities of platters wobbling at 7,200rpm, flash technology is emerging as one of the safest and most practical storage mediums today. Current capacity tops out at about 8GB, but larger capacities are on the horizon.
You might need different backup software. Experts and owners often aren't crazy about the backup software that ships with external hard drives. However, you can always use other software.
Assume that eventually, your drive will fail. Many reviewers recommend that you choose two smaller drives – one as a backup to the other – instead of a single large drive. There's certainly safety in numbers, so the more repositories of important data you're able to find, the better you'll sleep at night. Reviewers uniformly agree that an external hard drive should be part of an overall backup strategy, which should also include backing up to removable media or storing important files online.
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