Which cloud service model requires the customer to manage the OS?

The Infrastructure as a Service (IaaS) model requires the customer to manage the operating system (OS) while the cloud service provider handles the underlying hardware and virtualization. In this model, users are responsible for the installation, configuration, and maintenance of the OS and any applications or middleware they choose to deploy. This level of control allows customers to customize their environment to meet specific requirements, as they are essentially renting virtualized hardware and software resources.

In contrast, other service models offer varying degrees of management. For example, Platform as a Service (PaaS) abstracts the underlying infrastructure and offers a platform for developers to build applications without having to manage the OS. Software as a Service (SaaS) provides fully managed applications that are accessed via the internet, with no responsibility on the customer's part for managing the OS or underlying infrastructure. Emerging service models like Quantum as a Service (QaaS) also abstract much of the underlying complexity and do not require customer OS management.

In summary, IaaS distinctly places the responsibility of OS management on the customer, which is why it fits the criteria outlined in the question.