Which responsibility does Azure handle across all service models (IaaS, PaaS, SaaS)?

Azure is responsible for the physical infrastructure across all service models (IaaS, PaaS, SaaS). This includes the physical servers, networking, and data centers. This shared responsibility is a core tenet of cloud computing, where the cloud provider manages the underlying hardware. Guest OS patching is a responsibility that varies by service model; in IaaS, the user typically handles it, while in PaaS and SaaS, Azure often manages it. Data backup scheduling is generally a shared responsibility, with the user configuring backups and Azure providing the underlying storage. User permissions are almost always the customer's responsibility, as they control access to their resources and data within Azure.