How do IaaS, PaaS, and SaaS divide operational responsibility?

IaaS provides infrastructure such as virtual machines and networking while the customer typically manages the operating system and application stack. PaaS manages more of the runtime and deployment platform, letting the customer focus on application and data responsibilities. SaaS provides a finished application with customer configuration and access management. The exact boundary depends on the service contract. Managed services reduce specific operational tasks but do not remove responsibility for permissions, data handling, configuration, resilience, and understanding the provider’s guarantees.