How does System Call Work?
Here is the detailed explanation step by step how system call work:
- User need special resources : Sometimes programs need to do some special things which can’t be done without the permission of OS like reading from a file, writing to a file , getting any information from the hardware or requesting a space in memory.
- Program makes a system call request : There are special predefined instruction to make a request to the operating system. These instruction are nothing but just a “system call”. The program uses these system calls in its code when needed.
- Operating system sees the system call : When the OS sees the system call then it recongnises that the program need help at this time so it temporarily stop the program execution and give all the control to special part of itself called ‘Kernel’ . Now ‘Kernel’ solve the need of program.
- Operating system performs the operations :Now the operating system perform the operation which is requested by program . Example : reading content from a file etc.
- Operating system give control back to the program : After performing the special operation, OS give control back to the program for further execution of program .
Introduction of System Call
In computing, 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. A system call is a way for programs to interact with the operating system. A computer program makes a system call when it makes a request to the operating system’s kernel. System call provides the services of the operating system to the user programs via Application Program Interface(API). It provides an interface between a process and an operating system to allow user-level processes to request services of the operating system. System calls are the only entry points into the kernel system. All programs needing resources must use system calls.
A user program can interact with the operating system using a system call. A number of services are requested by the program, and the OS responds by launching a number of systems calls to fulfill the request. A system call can be written in high-level languages like C or Pascal or in assembly language. If a high-level language is used, the operating system may directly invoke system calls, which are predefined functions.
A system call is a mechanism used by programs to request services from the operating system (OS). In simpler terms, it is a way for a program to interact with the underlying system, such as accessing hardware resources or performing privileged operations.
A system call is initiated by the program executing a specific instruction, which triggers a switch to kernel mode, allowing the program to request a service from the OS. The OS then handles the request, performs the necessary operations, and returns the result back to the program.
System calls are essential for the proper functioning of an operating system, as they provide a standardized way for programs to access system resources. Without system calls, each program would need to implement its own methods for accessing hardware and system services, leading to inconsistent and error-prone behavior.