A system call is a programmatic way in which a computer program requests a service from the kernel of the operating system it is executed on. It is a way for programs to interact with the operating system and access hardware resources or perform privileged operations. System calls provide an interface between a process and an operating system to allow user-level processes to request services of the operating system. They are the only entry points into the kernel system.
System calls can be written in assembly language or a high-level language like C or Pascal. They are predefined functions that the operating system may directly invoke if a high-level language is used. Examples of system calls include accessing a hard disk drive, creating and executing new processes, and communication with integral kernel services such as process scheduling.
In summary, a system call is a mechanism that provides the interface between a process and the operating system, allowing a computer program to request a service from the kernel of the operating system it is executed on. It is a way for programs to interact with the underlying system, such as accessing hardware resources or performing privileged operations.
