Last Updated on March 2, 2023 by Prepbytes
System calls are a way for programs to interact with the operating system’s kernel. They provide a standardized interface for executing system-level functions, such as process management, file access, network communication, and memory allocation. Programs make system calls by issuing specific requests to the operating system, which then carries out the requested action and returns a result. In this blog we will discuss the types of system calls in os , the need for system calls in os, working of system calls.
What are System Calls in OS?
System calls are a crucial aspect of an operating system (OS) as they provide a bridge between the applications and the underlying hardware. They are the basic building blocks that allow a program to request and perform a service provided by the OS. In simple terms, a system call is a request made by a user-level program to the operating system to perform a specific task, such as allocating memory, creating a new process, reading or writing a file, or opening a network socket.
The system call interface is the entry point for a program to interact with the operating system. When a program makes a system call, it is transferring control from the user mode to the kernel mode. The kernel mode is the privileged mode of operation in which the operating system executes, and it has access to all hardware resources. By making a system call, a program is asking the operating system to perform a task on its behalf, such as reading or writing data to a file, allocating memory, or creating a new process.
System calls are defined in the API of the operating system and are usually written in a low-level language such as C or Assembly. These system calls are designed to be as simple and efficient as possible so that they can be executed quickly. They are usually implemented as a software interrupt or a trap, which transfers control from the user-level program to the operating system.
Why do we need System Calls in OS?
System calls in OS are an essential part of an operating system (OS) as they provide a means for applications to interact with the underlying hardware. There are several reasons why system calls are necessary:
- Resource Access: Applications need to access system resources such as memory, files, and networks. System calls provide a standardized interface for applications to request these resources from the OS.
- Task Execution: Applications may require the execution of tasks that are outside their control, such as creating a new process, managing processes, or scheduling tasks. System calls provide a way for applications to delegate these tasks to the OS.
- Security: System calls help to maintain the security of the operating system by enforcing access controls and preventing unauthorized access to sensitive information.
- Portability: System calls provide a standard interface for applications to interact with the OS, regardless of the underlying hardware. This makes it easier to write cross-platform applications and ensures that applications can run on different platforms.
- Stability: System calls help to ensure the stability of the operating system by separating user-level applications from the OS. If a user-level application crashes, it will not affect the stability of the operating system as the operating system is running in a separate mode.
- Performance: System calls are optimized for performance, as they are written in low-level languages and are designed to be as simple and efficient as possible.
System calls in os provide a standardized interface for applications to interact with the operating system, ensuring the security, stability, and performance of the system. They also make it possible for applications to access resources and delegate tasks to the OS, and they help to ensure the portability of applications across different platforms that is why we need system calls in os
Working of a System Call
A system call is a way for a user-level process to request services from the kernel (operating system). The process makes a request to the operating system through a system call by executing a special instruction that triggers the operating system to perform the requested service.
Here’s a high-level diagram explaining the working of a system call:
- User-level process: The process executing in user mode needs to perform a specific operation that requires the services of the operating system.
- System call request: The process makes a request to the operating system by executing a special instruction, typically through a library function (e.g. read(), write(), open(), etc.).
- Interrupt: The system call instruction triggers a software interrupt, causing the processor to switch from user mode to kernel mode.
- System Call Handler: The operating system has a system call handler routine that is executed in response to the interrupt. The system call handler performs the requested operation.
- System Services: The operating system provides the requested services to the process, such as accessing hardware resources or allocating memory.
- Return to User Mode: The processor switches back to user mode, and the results of the system calls are returned to the user-level process.
This diagram provides a simplified explanation of the working of a system calls in os. In actual implementation, the details may vary depending on the operating system and the architecture of the system.
Types of System Calls in OS
These are the types of system calls in os and mainly they are five types:
-
Process Control
Process control system calls: These system calls are used to create, manage, and control processes. Examples include fork(), exec(), wait(), kill(), and getpid(). -
File Management
Device management system calls: These system calls are used to manage and manipulate I/O devices such as printers, keyboards, and disk drives. Examples include ioctl() and select(). -
Device Management
Device management system calls: These system calls are used to manage and manipulate I/O devices such as printers, keyboards, and disk drives. Examples include ioctl() and select(). -
Information Management
Information maintenance system calls: These system calls are used to retrieve information about the system, the processes running on the system, and the status of various resources. Examples include getuid(), getgid(), and getpid(). -
Communication
These system calls are used for inter-process communication (IPC) and resource working. Examples include socket(), bind(), listen(), and accept().
Examples Of System Calls in Windows and Linux:
These are the example of system calls in os :
| Types of SystemCalls | Windows | Linux |
|---|---|---|
| ExitProcess() | exit() | |
| Process Control | CreateProcess() | fork() |
| WaitForSingleObject() | wait() | |
| CreateFile() | open() | |
| File Management | ReadFile() | read() |
| WriteFile() | write() | |
| CloseHandle() | close() | |
| SetConsoleMode() | ioctl() | |
| Device Management | ReadConsole() | read() |
| WriteConsole() | write() | |
| SetTimer() | alarm() | |
| Information Maintenance | GetCurrentProcessID() | getpid() |
| Sleep() | sleep() | |
| CreatePipe() | pipe() | |
| Communication | CreateFileMapping() | shmget() |
| MapViewOfFile() | mmap() |
Summary
System calls in os are a crucial aspect of an operating system and play a critical role in allowing programs to interact with the operating system’s kernel. They provide a standardized interface for executing system-level functions, such as process management, file access, network communication, and memory allocation. System calls in os are designed to be as simple and efficient as possible, and they help to maintain the separation between the user-level programs and the operating system. This separation is important for ensuring the stability and security of the operating system.
Frequently Asked Questions(FAQ)
Question 1) What are the different types of system calls in os?
Answer: There are various types of system calls in operating systems, including process control system calls, file management system calls, device management system calls, information maintenance system calls, and communication system calls.
Question 2) Why do processes need to make system calls?
Answer: Processes make system calls to request services from the operating system’s kernel. These services can include creating new processes, reading or writing files, allocating memory, or communicating with other processes.
Question 3) What is the purpose of system calls in os?
Answer: The purpose of system calls in operating systems is to provide a standardized interface between user-level processes and the operating system’s kernel. This allows processes to request services from the kernel in a uniform and controlled manner.
Question 4) How do processes make system calls in os (operating system)?
Answer: Processes make system calls by executing specific functions or routines that are provided by the operating system’s libraries. These functions are usually implemented in assembly language and invoke a software interrupt to switch from user mode to kernel mode, allowing the process to access the operating system’s kernel and request its services.
Question 5) What happens when a process makes a system calls in os?
Answer: When a process makes a system call, the operating system’s kernel performs the requested task and returns control to the user-level process, typically with a status code indicating whether the call was successful or not.