In 2004, Sun Microsystems revealed a radical plan to shake up the computing industry. It would build a series of large data centers and sell access to the computers inside them for $1 per hour.

What is this thing called "cloud computing"? It's nothing new - that much is certain. Software vendors have been offering applications "hosted" off-site for years. The idea of computer services as a kind of managed utility dates back to the 1960s at least. Salesforce.com, founded in 1999, based its entire business model on the cloud, even if it didn't use the word at the time. Since then, we've seen a variety of takes on what came to be known as Software as a Service, or SaaS. That's now been supplanted by "the cloud," a term which refers to any number of apps that reside in huge banks of servers located far from the client.