Can you explain what system calls are in an operating system?

System calls are an interface between user programs and the kernel of the operating system. They allow programs to request the OS to perform operations that require kernel privileges, such as working with files, managing processes, network operations, etc.

When a program invokes a system call, a switch occurs from user mode to kernel mode, where the OS performs the necessary operation and returns the result. This ensures the security and stability of the system, as direct access to hardware and critical resources is restricted.

An example of a system call in Linux is open() for opening a file, read() for reading data, fork() for creating a new process.