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Difference between system call and library call

  • Difficulty Level : Medium
  • Last Updated : 16 Jun, 2021

1. System Call :
There are two modes in the computer system one is user mode and another is kernel mode. In computer system there are different types of processes that are running on a computer system. When a user runs an application it is said to be in user mode or computer is in user mode.  When there is a requirement of hardware resource, the process sends a request to the kernel to get the process access and then computer enters in kernel mode. These requests are sent by using system call. The computer switches between these two mode frequently. Whenever the task is completed the computer goes back to the user mode from kernel mode. This mode of transition is called context switching.

2. Library Call :
A Library call is a kind of request to use a specific piece of function that is defined in a programming library. A library file contains code data file, object file that are packed into one file for use. To make a library call, library should be imported first. The library call may be depended on the system call to complete the task.
 

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Difference Between System Call And Library Call :



S.no        

SYSTEM CALL

LIBRARY CALL

1.A system call is a request made by the program to enter into kernel mode to access a process..A library call is a request made by the program to access a library function defined in a programming library.
2.In kernel mode the programs are directly accessible to the memory and hardware resources.In user mode, the programs cannot directly accessible to the memory and hardware resources.
3.In system call, the mode is executed or switches from user mode to Kernel mode.In library call, the mode is executed in user mode only.
4.In system call the execution process speed is slower than the library call because there is a mode of transition called context switching.In library call the execution process speed is faster than the system call because there is no mode of context switching.
5.A system call is a function provided by the kernel to enter into the kernel mode to access the hardware resources.A Library call is a function provided by the programming library to perform a task.
6.System call are the entry points of the kernel, and therefore they are not linked to the program.Library functions are linked into your program.
7.A system call is not portable.A library call is portable.
8.System call have more privileges than library calls because it runs in a supervisory mode.Library call have less privileges than system calls because it is runs in a user mode only. 
9.System calls are provided by the system and are executed by the system kernel.Library calls included the ANSI C standard library. 
10.In system call all functions are a part of the kernel. In library call all library functions are a part of the standard library file of programming languages. 
11.Whenever a program requires the memory or hardware resources, it directly sends a request to the kernel to get the process access by using a system call.

Whenever a programmer or a developer uses a specific library function, the programmer has to invoke or call the library function first by including a header file into his program. The preprocessor ( # ) directives helps to include header files. Some useful header files are :-

1. #include<stdio.h>

2. #include<math.h>

3. #include<conio.h>

12.

Examples of system calls are – 

1. fork() 



2. exec() 

Example of Library call are –

1. fopen()

2. fclose()

3. scanf()

4. printf() 

 

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