User Mode vs Kernel Mode - aryanjoshi0823/5143-Operating-System GitHub Wiki

There are two modes of operation in an operating system:

1. User Mode: Used for running user applications.
2. Kernel Mode: Used for executing operating system-level tasks.

These modes are determined by a mode bit:

• 1 for user mode.
• 0 for kernel mode.

Transitions between these modes occur during system calls or interrupts.

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User Mode

The system operates in user mode when executing user applications like text editors or web browsers. A transition to kernel mode happens when:

• Key Characteristics:

  • The mode bit is set to 1.
  • Restricted access to hardware and system resources.
  • Errors in user mode affect only the application, not the entire system.

• Example: A user application requesting to save a file invokes a system call, switching to kernel mode.

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Kernel Mode

Kernel mode is required for executing operating system services and privileged instructions like hardware management.

• Key Characteristics:

  • The mode bit is set to 0.
  • Full access to system hardware and resources.
  • Can execute privileged instructions like interrupt handling and I/O management.
  • Errors in kernel mode can affect the entire system.

• Example: Tasks like managing process scheduling and device drivers occur in kernel mode.