A terabyte may seem a lot to those who remember that, only 20 years ago, a 10Mbyte IBM PC/XT was considered impressive. However, you can now get external hard drives that store 250Gbytes for less than £150, and a portable enclosure can easily store half a terabyte. Given the consistent increases in drive capacity, multi-terabyte drives cannot be far away.
There has been a huge explosion in the external hard drive market over the past year. One of the many reasons is the increasing number of mobile PC users who need portable storage.
Today's high-spec portable PCs now have large hard drives and no convenient way of backing them up. Some models, such as the popular IBM Thinkpad X31 and similar wireless notebooks, do not have built-in CD or DVD writers, and even if they did, a back-up would require multiple discs. But they do have Firewire and probably USB 2.0 ports, which makes backing up to an external hard drive convenient.
Indeed, users can probably fit half a dozen disc images on a cheap external system using Norton Ghost, Acronis Trueimage or a similar program. As these systems are portable, they can also be used to back up one or more desktop PCs.
Of course, it is particularly important to back up notebook PCs that are used on the road. These machines are very susceptible to data loss because they tend to get dropped and are all too easily stolen.
Until recently, the back-up would have been done using some type of removable format, probably from Iomega, or CD or DVD-Rom. Today's external hard drives beat these for convenience, and they are very competitive on price.
The leading suppliers of external drives include LaCie, Maxtor, and Western Digital. Ximeta's Netdisk models can be attached to individual PCs or to small networks via a network switch. Some systems offer Raid storage.
There are, inevitably, drawbacks. Companies that have already adopted external hard drives have seen bottlenecks when transferring large files, data corruption and drive failures.
There is also the risk of losing control of large amounts of corporate data. Some companies are already alarmed about the risk represented by USB pen drives and portable music players, such as Apple's iPod, which also work as portable hard drives. But staff who can currently walk off with 15Gbytes of corporate data will soon be able to walk away with 1Tbyte of information.
Jack Schofield is computer editor at the Guardian