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Traps and System Calls in Operating System (OS)

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Traps and system calls are two mechanisms used by an operating system (OS) to perform privileged operations and interact with user-level programs. Here is an overview of each mechanism:

  1. Traps: A trap is an interrupt generated by the CPU when a user-level program attempts to execute a privileged instruction or encounters an error. When a trap occurs, the CPU transfers control to the kernel and executes a trap handler. The trap handler checks the type of trap and takes appropriate action, such as terminating the program or performing a privileged operation on behalf of the program.
  2. System calls: A system call is a request made by a user-level program to the OS to perform a privileged operation, such as reading from or writing to a file or allocating memory. To make a system call, the program executes a special instruction that triggers a software interrupt. The OS then transfers control to the kernel and executes a system call handler. The system call handler checks the type of system call and takes appropriate action, such as reading from a file or allocating memory.
  3. Traps and system calls are similar in that they both involve transferring control to the kernel to perform privileged operations. However, traps are usually generated automatically by the CPU when a program encounters an error or attempts to execute a privileged instruction, while system calls are initiated by the program itself to request privileged operations.

In summary, traps and system calls are essential mechanisms used by an operating system to ensure that privileged operations are performed securely and efficiently. Understanding how these mechanisms work is important for developing operating systems and writing programs that interact with them.

On the off chance that Operating System (OS) is secured, how does the program request administrations from OS? Client programs can’t call capacities inside the working framework’s memory, since it can’t see those territories of memory. 

An extraordinary client mode machine guidance, known as TRAP guidance, causes an exemption, switches CPU mode to Kernel mode, and starts the handler for TRAP guidance. 

To request specific help from OS, the client program places esteem in machine registers to show what administration it requires. At that point, it executes TRAP guidance, which changes CPU mode to advantaged mode and moves execution to the TRAP handler in OS’s memory. 

OS checks solicitation, and performs it, utilizing the dispatch table to pass control to one of a lot of OS administration schedules. At the point when the administration has been played out, OS returns control to the program, bringing down benefits back to client mode. Hence, activity-just approaches favored OS through solitary, all-around ensured section points. This component for acquiring OS administrations is known as System Call. The arrangement of accessible framework calls is known as the Operating System’s Application Program Interface or API.

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Last Updated : 04 Apr, 2023
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