THE "cloud" in cloud computing comes from terminology used to describe large networks such as the internet. Rather than data being stored in and accessed from the drive of an individual computer, that data is held off in the "cloud" of the network.

Cloud computing as a term generally refers to any very large network that can manage large amounts of information and a multitude of applications for multiple users - for example, a grid network (lots of individual computer servers) in a data centre - where applications and services are stored and accessed by computer users, and data may be shared among users. Some describe cloud computing as an architecture for setting up a grid - in other words, a subset of grid computing.

Web users make use of data, applications and services like this all the time - think of online applications such as Google Write or photo storage sites such as Flickr.

But in cloud computing, users tend to be enterprises and large organisations, the cloud is firewalled and access limited to employees or members of the organisation. The cloud often makes heavy use of "virtualisation", where single computers are set up to run several self-contained operating systems at once, so that they appear to the network to be several "real" computers, and can manage information more efficiently at lower cost. The cloud can do massive computing tasks by spreading out the job between all the cheaper machines and virtual machines in the cloud. The end result is that an organisation has access to supercomputing power, but in a more versatile and cost-effective form.

At the moment, cloud computing is getting a lot of attention and a lot of hype. It has some detractors, but in general it does genuinely appear to be one of the hot new paradigms for computing, say analysts. Most of the big technology companies have cloud computing initiatives of some sort, some aimed at the business market, some at the end user via the internet. We may all have our heads in the cloud before too long.