National Institute of Standards and Technology (NIST) Definition of Cloud Computing (Draft)

National Institute of Standards and Technology (NIST) Definition of Cloud Computing (Draft) can be found in this website from NIST. This definition is very clear.

1. The NIST Definition of Cloud Computing (Draft) (pdf)

The essential services are

1. On-demand self-service
2. Broad network access 
3. Resource pooling. 
4. Rapid elasticity. 
5. Measured Service. 

Service Models:

1. Cloud Software as a Service (SaaS).
2. Cloud Platform as a Service (PaaS).
3. Cloud Infrastructure as a Service (IaaS).

Deployment Models:

1. Private cloud
2. Community cloud
3. Public cloud
4. Hybrid cloud

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