What is a key difference among the IaaS, PaaS, and SaaS cloud service models?

• A. IaaS provides virtualized hardware; PaaS provides a platform for deploying apps; SaaS delivers software over the Internet.
• B. IaaS provides software; PaaS provides hardware; SaaS provides networking.
• C. IaaS handles end-user applications; PaaS handles storage; SaaS handles security.
• D. IaaS manages the operating system; PaaS manages the user interface; SaaS manages the database.

Answer: (A)

The main idea here is how responsibility and what's being provided change across the three cloud service models. In IaaS you’re renting virtualized hardware—compute, storage, and networking. The provider handles the physical infrastructure and the virtualization layer, while you install and manage the operating system, runtimes, and applications. In PaaS you’re given a platform with built-in runtime and development tools; the provider takes care of the OS, middleware, and underlying infrastructure, and you focus on building and deploying your apps. In SaaS you’re using ready-made software delivered over the Internet; the provider handles everything from infrastructure to the application itself, and you simply use the software.

That’s why the best description is: IaaS provides virtualized hardware, PaaS provides a platform for deploying apps, and SaaS delivers software over the Internet. The other options mix up what each model provides or who manages which parts, so they don’t fit the standard division of responsibilities.