Why need of system call in os?

System calls are essential in an operating system because they provide a controlled interface for applications to interact with the hardware and system resources. They facilitate tasks such as file operations, process management, and memory allocation while ensuring security and stability by preventing user applications from directly accessing hardware. This abstraction allows developers to write programs without needing to understand the complexities of the underlying hardware. Overall, system calls enable effective multitasking, resource management, and user-level application functionality.