Differentiate between Application Programming Interfaces (APIs) and system calls.

Let us learn about the application programming interface.

Application programming interface

We know that multiple devices and applications share data between them. Some devices include online reservations and some in booking systems.

API (Application Programming Interface) is used to establish connectivity among devices and applications. However, it is an interface which takes the requests from the user and informs the system about what has to be done and returns the response back to the user.


Consider an online travel agency having information about multiple airlines. The travel agency interacts with the airline’s API.

The Application interface takes the requests from the customer to book seats and also select meals from the travel service to the airline system. Then, the API delivers the airline’s responses back to the online travel agency and they display the details to the users.

This is an example of real-world application for an API.

System call

System call provides an interface between user program and operating system.

When the user wants to give an instruction to the OS then it will do it through system calls. Or a user program can access the kernel which is a part of the OS through system calls.

It is a programmatic way in which a computer program requests a service from the kernel of the operating system.

Program executes in two modes, which are as follows −

  • User mode − Cannot access any hardware resources, which perform only the user operations.

  • Kernel mode − Can access hardware resources like RAM, Printer.

The processor in a computer switches between the two modes depending upon what types of code are running on the processor. A process running in the user mode cannot access the virtual addresses that are reserved for the operating system.

The system is in user mode when the operating system is running a user application such as handling a text editor. The transition from the user mode to kernel mode occurs, when the application requests the help of the operating system or an interrupt or a system call occurs.

The mode bit is set to 1 in the user mode. When a program needs any hardware resources, it needs to make a call to the kernel.

Through system call, the program will switch to the kernel. It will happen with the hardware resources in the kernel mode. After compilation of the work of hardware resources, it will again come back to user mode. When it will require hardware then only it will come to kernel mode.

Given below is the figure representing the structure of a system call in an operating system −

Due to security reasons, user applications are not given access to hardware resources, when they need to do any I/O or require some memory, it requests OS one of all these. This request is made through system calls.


The major differences between Application Programming Interface (API) and system call are as follows −

Application Program InterfaceSystem Call
API is a set of protocols, routines, and functions which allows the exchange data among various applications and devices.System call allows a program to request services from the kernel.
The protocols and functions in API that define the methods of communication among various components.It is a method which allows a program to request services from the operating system’s kernel.
It can be a web-based system, operating system, database or software library.It provides an interface between user programs and operating systems.

Updated on: 29-Nov-2021

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