Infrastructure as a Service (IaaS) provides the foundational computing components: virtualized hardware, storage, networking, and hypervisor resources. CompTIA A+ explains that customers using IaaS are responsible for installing and maintaining:
* The operating system
* Applications
* Patches, updates, and configurations
This model gives organizations maximum flexibility because they can build custom server environments without purchasing physical hardware.
In contrast:
* SaaS (A) provides fully managed applications-users do not manage OS or software.
* PaaS (B) provides a development platform and tools but does not allow OS management.
* XaaS (D) is a broad term meaning "anything as a service," not a specific model.
Thus, IaaS is the only model where OS-level control remains with the customer.