Another choice for backing up is across a network. Larger organisations will often choose to back up via centralised systems, querying individual systems for changes overnight. The advantage is that data is aggregated onto a backup server (or several) for storage.

All the individual storage options mentioned above are available, as well as heavy-duty choices such as robotic tape libraries, which can keep terabytes at a time easily available without human intervention.

Over the past several years online backup services such as LiveVault have sprung up providing hosted storage on internet-connected servers to which backups can be sent. Software or dedicated systems at a customer site track data changes and propagate them over a secure connection to the online backup service.

The extra logic is to minimise network traffic, partly to reduce costs and partly because even a fast corporate internet connection is typically a fraction of the bandwidth available on a Lan, so it's simply not practical to back up huge chunks of data across the internet.

The advantages of network backup come mostly from economies of scale in larger companies. For smaller systems network backup may still be useful, depending on the amount of data on each client machine. And centralised backups are much easier to track than ad-hoc backups occurring on individual workstations.

Doing the deed
By the time you come to consider software you should already have covered the steps described above. Your data should be well organised, along lines of size and importance, and you should have an idea of how often it changes, how much you generate and roughly when it can be archived offline (if at all).

Armed with that knowledge you probably have an idea what options are open to you in terms of storage. For home and small office users, that's the hard part. The next step is to take a backup, and restore it. This is vitally important, and comes before deciding on how often to back up, whether you need offsite backup and so on.

Run through the basic process of getting your data onto your backup medium, and restoring it. Note any little alterations or surprises in the process. This often overlooked and very basic sanity check is usually the difference between good and useless backups.

Whatever your schedules and policies, you need to understand what's involved in getting data off your system and back onto it. Once you've run through the process, give some thought to how it could be improved. Do you have all the data you need on the backup, or perhaps even too much data? Does it take an acceptable amount of time, and can it be easily automated or done manually on a regular basis?

Software options
Modern operating systems usually include some kind of backup utility for defining what to back up and schedule regular backup cycles. Linux distributions invariably include the Tar archiving utility, and compression utilities like gzip and bzip, which can be combined with a few simple commands to cover basic backup needs, and driven with scheduler software to provide a complete solution.

Windows includes a backup utility, and under XP it's sophisticated enough to cover the needs of most home users and small servers. Usefully, Windows backup includes a 'System state' backup option, which gathers together the system Registry and various other important Windows files, which is much simpler than backing up your whole Windows directory or hunting around for particular files holding important settings.

If your Registry becomes corrupted or an important file gets overwritten, you can recover from the most recent system state backup without restoring the whole system or reinstalling. System state backups are especially useful if image backups aren't appropriate for your situation.

Experiment with the backup utilities included with your OS before paying for additional software. Often these utilities are all you need to schedule your backups and, even if you need something more sophisticated, the exercise will help clarify your additional requirements. Again, it's about keeping it simple; don't introduce any more complexity than you need to keep your data safe.

Scheduling
There's a simple rule of thumb to remember when deciding on backup schedules: it's better to back up than not to back up. There's no point in instigating an impressive schedule that's swiftly ignored - and that's equally true on your home PC or a server at the office.

Having already organised your data you'll have some idea of how much needs to be backed up, and how often. Consider if the system will always be on; if it will you can probably schedule automatic backups overnight, if not you'll have to perform them manually. As a minimum, plan to back up all your data once a week, and ideally changes on a daily basis in between.

Keeping a copy offsite
It's a good idea to keep some of your backups physically separate from the systems hosting the active data. Fire, flood, theft and terrorism are fortunately uncommon, but should be accounted for nonetheless.

The simplest offsite backup is just taking backups from home to the office, or vice versa. For many modest applications this is adequate. You only need to consider specialist data storage services if your data is especially valuable or you require additional security - there's no point keeping your servers in a vault if the backups are on your desk at home.

For on-the-go backups of work at hand, web-based email services can be handy. There's a definite security concern, though. You don't know how secure your data is from prying eyes while it travels back and forth on the internet or when it's on your email provider's servers.

But if that's not a problem, the upside is that, once you've emailed a document to yourself, you have a copy you can access from anywhere with an internet connection, and that's probably hosted physically distant from your own system.

It's all about the data
Backing up is a boring business. It's time spent grudgingly because it seems mostly to legislate for equipment failure, malice and user error. But once your data is organised backing it up isn't complicated; it just takes a small amount of discipline to create and stick to a schedule.

And remember the two most important rules: a backup is better than no backup, and a backup isn't a backup until you've restored from it.

Image backup
So-called 'image' backups are bit-by-bit copies of entire hard disk partitions. A system is rebooted into a special version of Dos, where disk partitions may be backed up or restored.

Image backups are popular for performing multiple installs on the same hardware. It's easier for IT staff to configure one machine with all the preferred software and setups unique to an organisation and then copy that system, rather than hand craft each individual workstation.

Combined with Microsoft's Sysprep utility this offers a powerful mechanism for deploying preconfigured systems, and is how manufacturers offer slightly customised versions of Windows preinstalled on new PCs.

There are some drawbacks to image backups for the average user, however. For a start, a backup of a whole partition necessarily includes everything on it, whether it's unique data or not, which costs a lot of space. And if you restore onto different hardware, things may not work properly or at all. Given these caveats, image backups have a big advantage for convenience.

If your system suddenly gets corrupted, just boot into your image backup software and recover your latest image archive. There's no reinstalling the OS and hunting around the web for drivers. This is most advantageous on laptops, which often have specialised hardware, making reinstalls arduous.

They are also more prone to damage or loss, and typically have smaller hard disks than their desktop counterparts. The investment in an additional drive for your desktop and image backup software on your laptop can downgrade loss or damage to your laptop from major catastrophe to minor frustration.

Norton's Ghost is the most well-known image backup software for Windows. Ghost is a venerable and respected program but has been overtaken by more flexible alternatives. Acronis True Image beats Ghost for convenience largely because partitions - even the active system partition - can be backed up from within Windows itself, cutting out the tedious step of booting into a restricted Dos environment to create a backup.

Besides recovering from data loss, image backup software makes it much easier to migrate to a new hard disk. Both Ghost and True Image offer the option of restoring to larger partitions and different disks, which alone saves a lot of frustration during hard drive upgrades.