Which model allows the provider to manage both hardware and operating systems but not application software?

The correct choice is Platform as a Service (PaaS). This model provides a computing platform that includes tools and services for application development, enabling developers to build, deploy, and manage applications without dealing with the complexities of the underlying hardware and operating system.

Under PaaS, the cloud provider handles the management of the hardware and the operating system, ensuring that they are up to date and secure. However, users are responsible for managing the applications they develop and any associated data. This allows developers to focus primarily on application development rather than the infrastructure.

In contrast, Software as a Service (SaaS) typically allows users to access software applications managed entirely by the provider, while Infrastructure as a Service (IaaS) gives users more control over hardware resources and often includes the operating system, in addition to the ability to install and manage any application software they require. Network as a Service (NaaS) focuses on networking resources and services, rather than application or hardware management. Hence, PaaS is the most accurate model for managing hardware and operating systems without concerning application software.