There is now a greater choice of external or mobile storage solutions than ever before. Fujitsu, Maxtor, Seagate and Western Digital all offer external drives; only Hitachi does not. There are an enormous number of independent companies supplying cases with USB and/or FireWire.

The main purpose of an external hard drive is to facilitate the storage of large amounts of data independent of a single PC and to allow several PCs to be backed up to a single, portable storage device.

The glossy literature supplied by the drive manufacturers makes a number of good points. The volume of data now being held on home and office computer systems is growing all the time. This is due, on the one hand, to the space requirements of digital media such as photographs (4 - 5 megapixels is already standard) and the increased popularity of digital video and music. On the other hand, the popularity of broadband DSL means that hard disk space can be filled much faster. Not only is there much more digital data available today; it is also being distributed much faster around the world.

External hard disks have also proved to be superbly suited to the storage of data for use on digital multimedia systems in our living rooms. Just think of the next generation of set-top boxes that can play video and music from an external data store via a USB or FireWire interface, or can record TV programs onto an external hard drive.

You have the option of removing the hard disk at any time from its case and installing it in your PC. However, as this step normally voids the manufacturer's warranty, you should think twice before doing so.