Mumbai University > Computer Engineering > Sem 5 > Operating System

Marks: 5M

Years: May 2016

• System calls provide an interface to the services made available by an operating system.

• We know that there are two main modes in the operation of the system, that is the user mode and kernel mode.

  • User mode: All user processes are executed.
  • System mode: All privileged operations are executed.

• However many a times user-mode programs need to execute some privileged operations in kernel mode. Since processor prevents direct access to kernel-mode functions, we need to use an interface.

• Definition: System calls provide an interface to the services made available by an operating system.

• System calls expose all kernel functionalities that user-mode programs require.

• The main advantage of system calls is security. Due to system calls a user program is not able to enter into the OS or any other users region.

• Similarly, I/O devices are free from any misuse by the user.