At the Oracle-Sun merger coming-out party, Larry Ellison asked “what is cloud computing?” suggesting it is the same old stuff of hardware, software and the Internet. Let me try to answer this question from various perspectives.
Cloud computing is an umbrella term that describes:
• Provisioning of compute services;
• Billing of the compute services
Provisioning of Compute Services:
Compute services are provisioned from a pool of hardware/networking/power. In other words you don’t buy or lease individual hardware and accoutrements; you simply use what you need from a pool of such resources.
The above describes the hardware layer; the software layer can also be shared or sandboxed. For example, Google offers a shared software layer, they provide the file system, key-value store, operating system, etc. Each of these are designed for multi-tenancy and all users run on this same shared software layer. Amazon provides a sandboxed approach. You get your own sandbox with your choice of software (including their options like SimpleDB and RDS, or your own like loading MySQL).
Billing of Computer Services:
There are two primary ways to pay for cloud computing: utility and subscription. Utility means you only pay for what you use. Subscription means you pay a recurring amount for the right to use something. Amazon provides examples of both. You can pay a subscription fee for an instance of a computer, regardless of how much you utilize it. But when paying for storage, you pay for usage only in a utility model. Private clouds might use chargeback billing, charging the departments that use their services according to utility or subscription models.
Cloud computing is an umbrella term that addresses the provisioning—ideally on demand—of compute resources, where the hardware layer supports multi-tenancy and the software layer can be shared or sandboxed. Cloud computing is usually billed, or charged back, according to a pay-as-you go or utility model, a subscription model, or a hybrid of the two.
Definition by Perspective (Consumer):
Cloud consumer: I only pay for what I need at the time in small increments (e.g. hourly or GB transferred) and many annoying things like automated back-ups are automatically handled for me. I have no fixed costs (hardware, software, switches), just variable costs.
Definition by Contrast:
Traditional (dare I say legacy) computing relies on dedicated resources. You might share the networking, but you have a dedicated computer and probably dedicated storage, not to mention dedicated software. Your average utilization of the system might be 10%, with the excess capacity waiting for spikes in usage or allocated for future growth. In other words, you are paying 10X more than you should.
If you have a better definition of cloud computing please provide it in the comments.
5 hours ago