When you add a software stack, such as an operating system and applications to the service, the model shifts to the Software as a Service (SaaS) model. Microsoft's Windows Azure Platform, discussed in Chapter 10, is best described as currently using SaaS model. When the service requires the client to use a complete hardware/software/application stack, it is using the most refined and restrictive service model, called the Platform as a Service (PaaS) model
this seems to contradict Chapter 1 where the most restrictive model is actually SaaS and PaaS is open enough to allow apps to be developed and deployed using the stack provided by the PaaS .
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