There are so many definitions of cloud computing, it reminds one of the ancient parable of the blind men and the elephant, in which each man grabbed a different part of the elephant. Because none of them saw the whole creature, each took it to be something quite different. Many of the definitions focus on a part rather than the whole, and therefore they miss the whole story.
The US National Institute of Standards and Technology (NIST) has recently published a draft definition:
"Cloud computing is a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction."
NIST specifies five essential characteristics:
NIST defines four deployment models:
- On-demand self-service
- Broad network access
- Resource pooling
- Rapid elasticity
- Measured service
- Private cloud – operated solely for a single organization.
- Community cloud – shared by several organizations with shared concerns
- Public cloud – made available to the general public and/or commerce and industry
- Hybrid cloud – a composition of two or more of the above types of cloud, interlinked in some way
A more general definition of ‘cloud’ looks at cloud computing in the context of the development of a global,
shared computing infrastructure on the WorldWide Web, where businesses and individuals interact.
“The whole point of cloud computing is to be able to operate in the cloud — in that global, 24×7, connected universe where you can instantly reach and interact with your customers, your partners and your mobile employees, as well as tapping into an expanding cornucopia of third-party resources and services that can help you achieve business results faster, better and at lower cost. Those who say that cloud is just a deployment choice, just a technology option, have shut their eyes to the wider opportunity and potential that the cloud context opens up. They’re still building application platforms and business systems that are designed without any acknowledgement of that global web of connections and resources — as if in today’s business environment, being connected is just an afterthought, an optional extra. Maybe for some applications it is, but their numbers are shrinking daily.”