What is Cloud Computing?

Cloud Computing is THE hot topic in the IT industry at the moment.  We're in the middle of a paradigm shift, and everybody wants to be part of the action.  That means that almost every provider is picking up whatever they've got and re-branding it as "The Cloud", when often it's the same old software, but hosted on the Internet somewhere, or the same old outsourcing services, but just relabelled.  Doing a Google search doesn't help you much either!  You'll find at least 27 different definitions of Cloud Computing, and an awful lot of confusing diagrams and jargon.  As I write this page, the top 3 paid entries in a Google search for "Cloud Computing" give me:
  • A major hardware vendor explaining how to "build on-premises cloud services", "consume off-premises services securely", how  things should be "immediate, interactive, connected and fluid" and how they have a "flexible Hybrid delivery model".
  • An Internet service Provider who provides "on-demand IT and communication services" and offers a free Cloud Computing guide for download (rather than explaining what it is on their site).
  • A dedicated hosting company that starts their explanation "Cloud Computing, or IaaS" (so that they've redefined the topic as just infrastructure, when it actually covers applications and development platforms too)
It's all very confusing!

We think a good place to start is our Cloud Terminology page, or you won't go far wrong with Wikipedia.  Our own simple explanation is that:
"Cloud Computing gives you the ability to run your applications and access your data using only the Internet accessed from your PC, Mac or mobile device.  Apart from the web browser or user interface, no other local software or data storage is required."
Of course there are technical advantages of one Cloud technology approach over another, and we hope to help you differentiate a good Cloud provider from a bad one, or to see which companies are presenting their old style but hosted solutions as if they were Cloud Computing.    

We do think a proper definition of the topic would probably be a good thing, but sadly they all use more jargon and technical terms than we would  like.  The US Depart of Commerce's National Institute of Standards and Technology has a Draft (yes, it's only a draft so far) definition of Cloud Computing which is the best you'll find at the moment.  We recommend we all work from that rather than inventing definition number 28, but it comes with a health warning - it's full of jargon! 

You can read the full document, but we've extracted the key sections:

The NIST Definition of Cloud Computing
Essential Characteristics
Service Models
Deployment Models

See - The NIST Definition of Cloud Computing (Draft) - Special Publication 800-145 (Draft)