According to the U.S.
National Institute of Standards and Technology, cloud computing
consists of five
essential characteristics, three distinct service models, and four deployment
models.
Essential
Characteristics
On-Demand Self- Service
Resource Pooling
Rapid Elasticity
Measured Service
Broad Network Access
Service
Models
Service
Software-as-a-Service (SaaS)
Platform-as-a-Service
(PaaS)
Infrastructure-as-a-Service
(IaaS)
Deployment
Models
Public Cloud
Private Cloud
Community Cloud
Hybrid Cloud
Service Models
Software-as-a-Service
This term generally
refers to applications that are delivered to end users over the Internet or
broad band access. There
are hundreds of SaaS providers covering a wide variety of applications.
Oracle CRM On Demand,
Salesforce.com, and Google Apps are examples of the SaaS model.
Infrastructure-as-a-Service
Refers to computing
hardware (servers, storage, and network) delivered as a service. This
typically includes the
associated software as well, including operating systems, virtualization,
clustering, and so on.
Amazon Web Services, for example, offers their Elastic Compute Cloud
(EC2) for compute
servers, SimpleDB for database, and Simple Storage Service (S3) for storage.
Platform-as-a-Service
This model conveys how an
application development and deployment platform can be delivered
as a service to
developers, allowing them to quickly build and deploy an SaaS application for
end
users. These platforms
typically include database and middleware, and are often specific to a
language or API. For
example, Google AppEngine is based on Java and Python, EngineYard is
based on Ruby on Rails, and Force.com uses a
proprietary variation of Java.
Hope this help,
Chatchai
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