System call

Advanced Operating System

1. Advance Operating system Darakhshan Nayab MSC(IT) MS(Computer Science) Dept.of Computer Science

2. Content System Call
API
How System Call Works? Why do you need System Calls in OS? Types

3. System Call System Call provides an Interface between user program & Operating system. In computing, a system call is the programmatic way in which a computer program requests a service from the kernel of the operating system it is executed on. A system call is a way for programs to interact with the operating system.

4. API Application Program Interface(API) provides an interface between a process and operating system to allow user-level processes to request services of the operating system. System calls are the only entry points into the kernel system. All programs needing resources must use system calls.

5. How System Call Works? Step 1) The processes executed in the user mode till the time a system call interrupts it.
Step 2) After that, the system call is executed in the kernel-mode on a priority basis.

Step 3) Once system call execution is over, control returns to the user mode.,

Step 4) The execution of user processes resumed in Kernel mode.

6. Why do you need System Calls in OS? Reading and writing from files demand system calls.
If a file system wants to create or delete files, system calls are required.
System calls are used for the creation and management of new processes.
Network connections need system calls for sending and receiving packets.
Access to hardware devices like scanner, printer, need a system call.

7. Types Process Control
File Management
Device Management
Information Maintenance
Communications