The cloud, the grid, IaaS, PaaS, and SaaS
Excellent article from ArsTechnica "The Cloud: a short introduction". Visual clues to understand the concepts:
The lowest cloud tier is infrastructure-as-a-service (IaaS), which looks to the client like a dynamically scalable pool of compute and/or storage resources. The basic metered unit of IaaS is usually either a single virtual machine (e.g., Amazon EC2) or an abstract storage object of a certain size (e.g., Amazon S3).
Next up the ladder of abstraction is platform-as-a-service (PaaS), which provides API-level access to a cloud infrastructure layer. Examples of PaaS are Google AppEngine and Force.com....
The final and most popular tier of cloud service is software-as-a-service (SaaS). Google Apps and Salesforce.com are the two paradigmatic SaaS examples...
No need to write more, please, follow the link to the original article: ArsTechnica "The Cloud: a short introduction"....
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