Supervisor Mode (Privileged Mode)

Supervisor mode or privileged mode is a computer system mode in which all instructions such as privileged instructions can be performed by the processor. Some of these privileged instructions are interrupt instructions, input output management etc

The privilege levels of different components in a system is given as follows −

The kernel is the most privileged part of the computer system. There are some privileged instructions that can only be executed in kernel mode or supervisor mode. The the privilege reduces for device drivers and applications respectively.

Features of Supervisor Mode

Some of the important features of supervisor mode are as follows −

• Supervisor mode handles different types of commands but mostly deals with privileged instructions.This mode is used by the operating system and has full access to all the system components.
• The system starts in supervisor mode when it boots. This allows various programs complete access to the system hardware such as bootloader, BIOS, operating system etc.
• The operating system selects supervisor mode for the low level tasks that require complete access to the system hardware.
• Supervisor mode provides the essential barrier between applications and system hardware .It also provides access to various peripherals, memory management hardware etc.
• Supervisor mode can create memory address spaces as well as update them. It can also access the memory address spaces of other operations.
• Various interrupts can be enabled or disabled using the supervisor mode. It also contributes to the loading of the processor status.
• The supervisor mode can access the various data structures available inside the operating system.

Necessity of Supervisor Mode in Operating System

The lack of a supervisor mode in an operating system can cause serious problems. Some of these are −

• A running user program can accidentally wipe out the operating system by overwriting it with user data.
• Multiple processes can write in the same system at the same time, with disastrous results.