Cloud computing. If you haven't heard of it yet, you don't read any of the popular IT trade publications. Good for you. Cloud computing is most certainly a hot topic these days. It even has worked its way into day-to-day jargon–as in "We can host XYZ on our cloud, and you can continue to run PQS on your cloud." It fits in very nicely with other popular concepts such as SOA, Web 2.0, and Software as a Service (SaaS), for instance, "Cloud computing really just extends SOA onto Web 2.0 and provides the basis for Software as a Service"–or some such thing. Cloud computing also has a life outside of computer pundits. Cloud services are offered by Amazon, Google, Yahoo, Microsoft, HP, IBM, and others. Salesforce.com has been extremely successful providing a hosted–SaaS–customer relationship manager (CRM) solution. The last I looked it claimed nearly 45,000 customers. Not bad for a first-generation, nontraditional solution.

Now, let's see whether we can figure out exactly what we mean by cloud computing. If you have been around the IT world for any time at all, you know the standard network symbol for the Internet is a cloud. So, cloud computing is software or services made available over the Internet. A provider of cloud computing services offers a single point of entry to the services it provides. That single point of entry is accessed via HTTP over the Internet.

What lies behind that single point of entry is essentially a black box as far as the consumer of the service is concerned. It may be a robust data center with multiple redundancies and a 24/7 service staff. It may be servers dedicated to a single customer, or it may be a grid of low-cost machines that spread processing and services over the entire grid. More about what's behind the scenes later, but when you opt for cloud computing, you are opting for a solution in which you have no ownership or control of the infrastructure.