What is the Difference Between User Mode and Kernel Mode?

User mode and kernel mode are two distinct modes in which a computer processor operates, depending on the type of code being executed and the level of access to system resources.

• User mode: This is a restricted mode where applications operate with limited access to system resources. Each application runs in isolation, ensuring that if one crashes, it doesn't affect other applications or the operating system. In user mode, applications have their own virtual address space, which is private and limited. If an application in user mode needs to access system resources, it must go through the operating system kernel using syscalls.
• Kernel mode: This is a privileged mode where core operating system components function with unrestricted access to system resources. All code running in kernel mode shares a single virtual address space, allowing processes to access system resources and perform privileged operations. Kernel mode is reserved for drivers and other critical system components. When a user-level application needs to perform an operation that requires kernel mode access, it must make a system call to the operating system kernel.

Key differences between user mode and kernel mode include:

1. Access to resources: In kernel mode, programs have direct and unrestricted access to system resources, while in user mode, applications have limited access and must go through the operating system kernel to access resources.
2. Memory protection: In user mode, each application has its own private virtual address space, ensuring that one application cannot modify another application's data. In kernel mode, all processes share a single virtual address space.
3. Isolation: In user mode, applications run in isolation, preventing one application's crash from affecting other applications or the operating system. In kernel mode, a crash in one component can potentially affect the entire operating system.

Comparative Table: User Mode vs Kernel Mode

Here is a table comparing User Mode and Kernel Mode:

In summary, User Mode is a restricted mode that limits access to system resources and is used for running applications. Kernel Mode, on the other hand, is a privileged mode that allows unrestricted access to system resources and is used for running core operating system components.