What is System Calls, Definitions, Types, Pros and Cons

Authored By: Deepali Mishra

A system call is a request made by a program to the operating system to perform a specific function or service. It is a way for a program to communicate with the operating system and request access to system resources or services.

There are several types of system calls, which can be classified based on their purpose and the level of access they provide to the operating system. Some common types of system calls include:

File system calls:

These allow a program to access and manipulate files and directories on the file system. Examples include open, read, and write.

Process control calls:

These allow a program to create, terminate, and control processes. Examples include fork, exec, and wait.

Communication calls:

These allow a program to communicate with other programs and devices, including inter-process communication (IPC) and networking. Examples include socket, bind, and listen.

Memory management calls:

These allow a program to allocate and deallocate memory, as well as to control the mapping of virtual memory to physical memory. Examples include malloc, mmap, and brk.

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There are several advantages to using system calls, including:

  1. Improved efficiency: System calls provide a direct and efficient way for a program to access system resources and services, as they are implemented in the operating system kernel and bypass the overhead of library functions.
  2. Improved security: System calls provide a way for the operating system to enforce security policies and prevent unauthorized access to system resources.
  3. Improved portability: Programs that use system calls can be easily ported to other operating systems, as long as the target operating system supports the same system calls.

However, there are also some potential drawbacks to using system calls, including:

  1. Overhead: The use of system calls can add additional overhead to the execution of a program, as they require a context switch between user space and kernel space.
  2. Complexity: The use of system calls can add an additional layer of complexity to the development process, as they require a thorough understanding of the operating system and its interfaces.
  3. Compatibility: Different operating systems may have different sets of system calls and different interfaces, which can limit the portability of programs that use system calls.

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In terms of real-time applications, system calls are used in a wide variety of contexts, including:

  1. File I/O: Programs use system calls to read and write files, including text files, binary files, and special files such as pipes and sockets.
  2. Process management: Programs use system calls to create and control processes, including forking, execing, and waiting for child processes to complete.
  3. Networking: Programs use system calls to create and manage network connections, including socket creation, binding, listening, and accepting incoming connections.
  4. Memory management: Programs use system calls to allocate and deallocate memory, as well as to control the mapping of virtual memory to physical memory.

Conclusion

In conclusion, system calls are a fundamental part of the operating system and are used by programs to request access to system resources and services. They offer advantages such as improved efficiency, security, and portability, but can also introduce overhead and complexity. Understanding the different types of system calls and their interfaces is an important skill for developers working with operating systems.

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