Lab

External Hard Disks

Hard disks that once seemed impossibly vast can fill up with files surprisingly quickly. It's important to have plenty of storage space, whether you want to shoot high-definition video, take photos in RAW format or convert all your music CDs into MP3 files.

An easy way to add storage to your computer is to plug in an external hard disk. These have two main advantages over internal disks. First, attaching an external disk is quicker and easier than replacing your computer's internal hard disk. Second, you can carry an external disk away from your computer, which means you can transfer large quantities of data to another location or keep a backup of your data away from your computer in case it's damaged or stolen.

This month we've tested six portable disks designed for use on the move with a laptop, and six larger, mains-powered disks designed for use on your desk. No matter how much data you need to store, we'll help you find the right disk.

Buying an external hard disk isn't simply a matter of choosing the biggest capacity at the lowest price. External hard disks vary in design, features and performance. Before you buy, it's important to decide whether you need a portable disk, how much storage space you need, which interfaces you want and whether you need backup software.

Get carried away

There are two main types of external hard disk: portable and desktop drives. Desktop hard disks have the highest capacities and the lowest cost per gigabyte, but they need to be plugged into the mains.

Portable disks are ideal if you need to carry your data with you or move it from one computer to another. They are based on laptop hard disks so they're lighter and smaller than their desktop counterparts, but they can't store as much and are more expensive per gigabyte. Most portable disks use 2in disks but some, such as LaCie's Little Disk, use a 1.8in disk. These are small but they're not as fast or as good value as their slightly larger counterparts.

Portable disks don't need a mains power supply, but some need to connect to two USB ports in order to draw enough power to run.

Space raiders

When deciding on your drive's capacity, the general rule is to buy as large a hard disk as you can afford. Two of the desktop disks in this month's Labs are 1TB or larger, while the rest have capacities of 500GB. The portable disks range in capacity from 60GB to 320GB. Most models are also available in other capacities, which we list in the tables on page 128. The table also shows the cost per gigabyte of each disk, making it easy to judge how much storage you're getting for your money.

Some external disks, such as Iomega's UltraMax Pro, consist of two internal hard disks configured as a RAID array. When configured as a RAID 0 array, the two disks appear to Windows as a single drive with the combined capacity of both disks. Data is written alternately to one disk then the other, which increases performance. If one disk were to fail, though, you would lose all your data. When set up in a RAID 1 configuration, data is mirrored across the two disks. This halves the available capacity, but if a single disk should fail, the other disk will retain a copy of your data.

Connection confusion

Many external hard disks, especially desktop models, offer a choice of interfaces. USB Hi-Speed ports are by far the most common and all PCs and laptops made in the past couple of years should have at least two. USB Hi-Speed is fast enough for most tasks but you may want to use a faster interface such as FireWire or eSATA if you deal with large amounts of data, such as HD or digital video. Many new computers come with FireWire 400 ports. Although FireWire 400 has a lower theoretical throughput than USB, it's faster when transferring files due to the way it works.

If your laptop or PC doesn't have FireWire 400, you'll need a FireWire 400 CardBus or PCI card. Most laptops have four-pin instead of six-pin FireWire 400 ports, so you may need a four-pin to six-pin FireWire cable. You can connect multiple FireWire disks to a computer by daisy- chaining them, but for this to work all the FireWire devices in your chain apart from the final one must have two six-pin ports.

FireWire 800 is even faster than FireWire 400 and, as our tests show, can approach or exceed the speeds of eSATA disks. Sadly, few hard disks and even fewer PCs have FireWire 800 ports. A FireWire 800 PCI card costs about £30, a CardBus adaptor costs £40 and an ExpressCard adaptor costs £60. FireWire 800 devices can be plugged into FireWire 400 ports with a £20 adaptor, but will run only at FireWire 400 speeds.

Finally, eSATA is the external version of the SATA/300 interface used by internal hard disks. An eSATA interface can be significantly faster than USB or FireWire and can sometimes match the speeds of internal SATA disks. A growing number of PCs now come with eSATA ports but, unlike FireWire, you're limited to one disk per eSATA port. The cheapest way to add ports is with a £5 PCI eSATA backplate, which plugs in to one of the SATA ports on your motherboard.

Softly does it

External hard disks are ideal for making backups of your important files. If you don't already use a backup program, it's worth considering the applications bundled with many disks.

Backup software should support scheduled backups so that you don't have to remember to copy your files over manually. It should keep older versions of your files in case you delete or change something by mistake on your internal hard disk. It should also support incremental backups so only those files that have changed since your last backup are copied, saving time.

Most of the backup programs bundled with these disks include at least one or two of these essential features, but the LaCie Backup Software program that comes with some LaCie disks is so basic that it's not much better than using Windows Explorer. The Maxtor Manager program included with Maxtor's disks is especially handy, as it can create a complete image of your internal hard disk.