Difference between System Call and Library Call

In computer programming, system calls and library calls are essential mechanisms used to interact with the underlying operating system and perform various operations. While they both involve invoking functions or routines, there are distinct differences between system calls and library calls. Understanding these differences is crucial for developers to efficiently utilize these mechanisms in their applications. This article explores the dissimilarities between system calls and library calls, shedding light on their respective characteristics and functionalities.

What is System Call?

A system call is a mechanism provided by the operating system that allows user-level programs to request services from the operating system kernel. It acts as an interface between the user-level application and the operating system. Here are some key characteristics of system calls:

  • Privilege: System calls are privileged operations that require a transition from user mode to kernel mode. They allow access to low-level operating system functionalities that are not directly accessible to user-level programs.

  • Functionality: System calls provide a wide range of services, including process management, file management, device I/O, memory allocation, and networking. They enable applications to perform critical operations that interact with the underlying hardware and resources.

  • Performance: System calls generally have higher overhead compared to library calls due to the transition from user mode to kernel mode. This transition involves context switching and can be relatively expensive in terms of time and resources.

  • Protection: System calls enforce security and access control mechanisms. The operating system verifies the permissions and validity of the request before executing the system call, ensuring the protection of system resources.

What is Library Call?

A library call refers to invoking a function or subroutine from a software library or framework. Libraries contain precompiled code that provides a set of reusable functions and routines to simplify programming tasks. Here are some key characteristics of library calls:

  • Accessibility: Library calls are accessible directly from the user-level program without the need for transitioning to kernel mode. They are typically part of application-specific libraries or system libraries that provide higher-level abstractions and functionalities.

  • Functionality: Library calls offer a specific set of functions or routines that can be used to perform common tasks, such as string manipulation, mathematical operations, data structures, and graphical operations. They provide ready-to-use functionalities to simplify application development.

  • Performance: Library calls generally have lower overhead compared to system calls since they are executed within the user-mode context. They involve direct function calls, avoiding the overhead of context switching and kernel-level operations.

  • Flexibility: Library calls provide a flexible and modular approach to software development. Developers can choose which libraries to include and utilize based on their application's requirements. Libraries can be shared across multiple applications, promoting code reuse and efficiency.

Difference between System Call and Library Call

Here's a table highlighting the difference between system calls and library calls:

System Call

Library Call


An interface provided by the operating system to interact with the kernel and request services

A function provided by a library to perform specific tasks.


Invoked using a specific syntax or assembly instruction, often requiring a transition to kernel mode.

Invoked using a normal function call within the user program.


Performs privileged operations and interacts with the underlying operating system resources

Provides higher-level functionalities to simplify programming tasks.


Provides low-level services like process management, file operations, network communication, etc.

Offers higher-level services and abstractions built on top of system calls.


Requires explicit permission and is subject to access control policies enforced by the operating system.

Generally accessible to any user program that includes the corresponding library.


Typically slower due to the overhead of context switching, as system calls involve transitioning to kernel mode.

Generally faster as library calls are executed in user mode without the overhead of context switching.


Implemented as a part of the operating system's kernel.

Implemented as pre-compiled code within libraries that are linked to user programs.


read(), write(), fork(), exec(), open(), close(), etc.

printf(), scanf(), strlen(), strcpy(), sort(), etc


System calls may vary across different operating systems or versions, requiring adaptation for portability

Library calls provide a consistent interface that can be used across different platforms, abstracting system-specific details


System calls are typically fixed and cannot be modified by the user.

Library calls can be extended or customized by creating additional functions or using function pointers.

Error Handling

System calls often return error codes or set specific error flags to indicate failures or exceptional conditions

Library calls may return error codes or use exceptions for error handling, depending on the programming language or library design.


In summary, system calls and library calls serve distinct purposes in software development. System calls facilitate direct interaction with the operating system kernel and access to privileged services, while library calls provide higher-level functionalities through reusable software libraries. Understanding the differences between these two mechanisms is crucial for developers to choose the appropriate approach based on their requirements, performance considerations, and portability needs.

Updated on: 12-Jul-2023


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