System calls in OS
System Calls in Operating System (OS)
A system call is a way for a user program to interface with the operating system. The program requests several services, and the OS responds by invoking a series of system calls to satisfy the request. A system call can be written in assembly language or a high-level language like C or Pascal. System calls are predefined functions that the operating system may directly invoke if a high-level language is used.
In this article, you will learn about the system calls in the operating system and discuss their types and many other things.
What is a System Call?
A system call is a method for a computer program to request a service from the kernel of the operating system on which it is running. A system call is a method of interacting with the operating system via programs. A system call is a request from computer software to an operating system's kernel.
The Application Program Interface (API) connects the operating system's functions to user programs. It acts as a link between the operating system and a process, allowing user-level programs to request operating system services. The kernel system can only be accessed using system calls. System calls are required for any programs that use resources.
How are system calls made?
When a computer software needs to access the operating system's kernel, it makes a system call. The system call uses an API to expose the operating system's services to user programs. It is the only method to access the kernel system. All programs or processes that require resources for execution must use system calls, as they serve as an interface between the operating system and user programs.
Below are some examples of how a system call varies from a user function.
- A system call function may create and use kernel processes to execute the asynchronous processing.
- A system call has greater authority than a standard subroutine. A system call with kernel-mode privilege executes in the kernel protection domain.
- System calls are not permitted to use shared libraries or any symbols that are not present in the kernel protection domain.
- The code and data for system calls are stored in global kernel memory.
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