No matter how large your hard disk, filling it up can take less time than you think. Even those who like to keep their homes clutter-free quickly become seasoned hoarders, as collections of software, digital photographs, video and music fill the computer's storage area to bursting point.

For people who can't bear to part with this material, the next stage is often to back up the files on a CD or DVD, but this can take time and means you have to split collections over several discs.

Fitting a new or extra hard disk inside the computer is also an option but, if you don't like the idea of opening the case and fiddling about, consider an external hard disk.

Apart from the benefit of not having to install it, external hard disks can be plugged in when needed and then stored tidily away. Many are portable, and this can be a practical way of transporting large files, such as home movies, to friends or relative's houses for viewing.

We've taken a look at six external hard disks, rating them on value for money, ease of use and how practical they are for carrying around.

Size matters
Before we talk about external hard disks any further we should make it clear that fitting an internal hard disk is by far the cheapest option. The problem with this is that you have to open up your computer and fiddle with the hard disk settings.

The first thing to decide is how much capacity you need. Ideally, you want the biggest hard disk you can afford but here are some guidelines to help you decide how much space you will need. Hard disk capacity is measured in gigabytes (Gb), which are equal to 1,024 megabytes (Mb).

Music, whether it's ripped from a CD or purchased online, eats up space at about 1Mb per minute of music, so an album saved in the MP3 format usually needs about 70Mb of space. Therefore 1Gb is going to hold (and this is a rule of thumb, not a precise measurement) about 14 standard albums.

If you're into digital video, or want to start recording TV programmes on your PC, you'll already know how much of a space-hog it can be. Raw, high-quality footage can take up an incredible 13Gb per hour, so you'll need the biggest disk you can get your hands on.

Life in the fast lane
With the huge amounts of information being transferred, you need a connection between the computer and hard disk that is fast enough to transfer the information quickly so you don't have to wait around all day.

There are two choices: USB 2 and FireWire. If you plan to use a USB2 external hard disk, make sure there's a USB2 socket on the computer and not USB1, which is about 40 times slower than USB2. The latest version of FireWire, on devices such as digital camcorders, can run about twice as fast as USB2.

The final issue to consider, although don't lose any sleep over it, is the disk speed. This is measured in revolutions per minute (RPM) and simply defines how quickly the computer can whiz around the disk to pick up or drop off data. Common speeds are 5,400RPM and 7,200RPM. If you're planning to edit video files straight from the disk, go for 7,200, for everything else 5,400 will be fine.

Freecom FHD-2 Pro
www.freecom.com
The first contender is also one of the smallest on test, both in size and capacity. It can store 20Gb of data and, at £104, gives a value for money ratio of £5.20 per gigabyte, which is quite pricey.

The Freecom FHD-2 Pro connects to your computer using USB2. It also draws its power from this connection so there is no need to carry a power adapter with you. There is some useful software supplied, including the Personal Media Suite, which can run software or open folders automatically when you connect it to your computer.

The large button on the top of the FHD-2 is used to synchronise with your computer. This means you don't have to remember which files need changing, as the computer makes sure the latest versions of files are used at all times. You can also compress or scramble the information on the disk for added security.

The FHD-2 has a brushed aluminium case which is light and strong. If you want to share digital video or photos with friends, the small size means it's easy to slip the FHD-2 Pro into a pocket. Windows XP computers require no installation discs but 98 and SE users will need to load some software from the supplied CD.

Siwara Pocket 20Gb
www.hki-systems.co.uk
The Siwara Pocket 20Gb is very similar to the Freecom FHD-2, but at £250 the price per gigabyte is a painful £12.30. However, it does have some fancy tricks up its sleeve.

The Siwara is designed for those looking for something on which to back up their hard disk. As you would expect, back-up software is included and it automatically checks your hard disk for new material when it's plugged in.

That means it copies only the files it has to, saving loads of time. The software doesn't compress the files and, while this takes up more space, it is much easier to recover your files in case of an accident.

You can also set the Siwara to create icons on the Desktop when it is plugged in making it easy to access, especially if you want to quickly copy some photos to show friends.

Equally useful is the CD Tower software. This makes a copy of a ripped CD on the external hard disk, saving you from carrying around lots of CDs. The only problem is that the tools used to stop consumers illegally sharing some CDs, and many games, prevents this feature from working.

The Siwara Pocket 20Gb is simplicity itself to set up and will work on Apple Mac computers as well as PCs. No power supply is needed, but the Siwara comes with a special USB cable that plugs into two sockets to make sure there is enough power.

SmartDisk FireLite 80Gb
www.smartdisk.com
The FireLite 80Gb is ideal if you want a simple external hard disk with a respectable amount of capacity. The larger capacity brings the price per gigabyte down to £2.25, half that of the Freecom FHD-2.

The status light alerts you when it is plugged into a slower USB1.1 socket, potentially a real time-saver. What lets the product down slightly, although only for those using Windows 98 or Me, is that you will have to download the software needed to install the hard disk.

The company's address is included in the manual but, given that the product costs almost £200, not including the CD is penny pinching of the lowest order.

One welcome feature is the inclusion of an extra power lead that plugs into your PC's keyboard socket. This is handy for those who already have several USB devices drawing power from the USB sockets. Unfortunately, the SmartDisk can't automatically switch to the mains supply when it is drawing insufficient power from the USB socket. Instead, users have to manually flick a switch.

Western Digital Media Center
www.westerndigital.com
With a capacity of 250Gb, the Media Center offers enough space for the most data-hungry programs, such as video editing. This pushes down the cost per gigabyte to 98p, making it the best value for money in pure storage terms.

The cost of this huge capacity is a lack of portability: in fact, there is a warning on the back of the case that says the Media Center is not designed as a portable device and any damage from using it in this way will void the warranty. That doesn't mean you have to keep it wrapped in cotton wool but, if you prefer to put it out of sight when not in use, move it with care.

You can connect the hard disk using FireWire or USB2. Uniquely in our test, there is an eight-in-one memory card reader on the top of the Media Center. You can use this as an ordinary card reader and access the files on your computer or set the Media Center to copy the files off the card at the touch of a button.

When you press the power off button, the Media Center automatically ensures that all current work is saved, preventing accidental loss of data. Considering its size, value for money and helpful extras, the Media Center had to be the winner in our test.

Ximeta Netdisk Mini
www.ximeta.com
The Ximeta Netdisk Mini is small enough to be carried around and, at £4.75 per gigabyte, offers twice the amount of storage available from the Siwara Pocket 20Gb for less money. It is slightly bigger than the Siwara and the Freecom disks, but is still light enough to be portable.

An external power supply is required so, if you want to access its contents on another computer, you'll have to remember to take the lead too. Connection is by USB2 and the installation software for Windows 2000, ME or XP is already on the hard disk, so no CDs or downloads are required.

Next to the USB socket is a network socket and this is where Ximeta offers something different to its rivals. Those who have two or more PCs linked together, with or without wires, can plug the Netdisk Mini directly into their network so the disk can be shared.

The Netdisk system requires a small program to be installed on each machine in order to access the disk but it gives you an extra amount of security, especially if you use it with a wireless network.

This software allows to you dictate whether individual computers can make changes to the files on the disk or whether it can just read them. This is particularly handy if the disk is to be accessed by younger users, who may decide that deleting your important files is more fun than playing games.

The Netdisk Mini wins points for pure home use, but a 40Gb disk may not be big enough for the whole family to share in the long term.

Ximeta Netdisk Office
www.ximeta.com
The Netdisk Mini's more advanced sibling is much bigger in every way. The amount of available space is 250Gb, equal to the Western Digital but with a slightly higher price per gigabyte of £1.24.

There is no question of running out of space with this hard disk unless you use it to store massive amounts of video. This is not a very portable disk, however, and is best used in one place. An external power adapter is required, so that's one more power socket you'll have to find, but it does allow the hard disk to rotate faster, giving speedier access to files.

Like its little brother, the Netdisk Office has a network connection as well as USB2. This device is designed for people who run a small business where data needs to be accessed by several users. It has enough network connections to share data between eight computers, and can even act as a hub, a device that directs traffic between computers, so you don't have to invest in a separate network.

Like the Mini, using the network connection necessitates installing software on each computer. It is also worth noting that data transfer is slower over a network connection than USB2.

If you only have one computer this is overkill and you would be better served by the Western Digital. But if you plan on adding more computers or a wireless access point this is definitely worth considering.

Outer space
Using your computer is only fun if you can create something special with it and nothing is more frustrating than running out of space halfway through editing a video. With a variety of prices and capacities it was hard to choose a winner, but the Western Digital wins for both features and capacity.

The huge 250Gb makes the price per gigabyte very low and you are unlikely to run out of storage space. The memory card reader is the icing on the cake. If you want the freedom to create music and video to your heart's content, an external hard disk is the answer.

DIY external storage
There's no reason why you can't use an old hard disk and a special case to make an external hard drive. You can buy the cases from websites such as www.dabs.com or www.scan.co.uk.

They are normally called external hard disk cases or enclosures. They can be bought for as little £25, offering a cheap alternative and a good way to make use of an old hard disk.

Online storage
If you have a broadband connection, storing your files online can be a very attractive idea. Some providers offer dedicated storage space, or you can make use of a new breed of email providers which offer large amounts of storage such as Gmail, Lycos and Hotmail.

One advantage of this kind of storage is that it is completely separate from your computer and less likely to be affected by crashes or viruses. On the other hand, you are relying on the company to keep your information safe, so research their reputation before you commit.

If you want to share photos there are online services that can do this for you. Check out our Sharing your photos online feature.