Definition
Kernel Mode
Kernel Mode (also known as privileged mode or supervisor mode) is a highly privileged execution state of the processor. It grants the operating system unrestricted access to all machine instructions and hardware resources.
The kernel resides in this state to perform its duties as a resource manager and hardware abstraction layer.
Usage
The CPU enters Kernel Mode to execute trusted OS code (the kernel) for:
- Interrupt Handling: Responding to asynchronous hardware signals.
- System Calls: Providing protected services requested by user processes (see User Mode for details).
- Exception Handling: Recovering from software errors (traps).
In this mode, the OS can modify Control Structures, manage memory via page tables, and communicate directly with I/O controllers.
Comparison
For a detailed comparison of execution privileges, see the User vs. Kernel Mode section.