We call them as Kernal Layer & User Layer also...!
A kernel is a software program which is used to access hardware components of a computer system. Kernel works as a middleware software for hardware and application software/user programs. Kernel mode is generally reserved for low level trusted functions of the operating system.
When a computer application is running, it is in the user mode. Some examples are word application, PowerPoint, reading a PDF file and browsing the internet. These are application programs so the computer is in user mode. When the process is in user mode and requires any hardware resource, that request is sent to the kernel. As there is a limited access to hardware
In summary, the main difference between kernel mode and user mode lies in the level of privilege and access to system resources. Kernel mode is reserved for critical system functions and operates with higher privilege, whereas user mode is where most applications and processes run, operating with restricted privilege and relying on the operating system for accessing system resources. The separation between these modes enhances system stability, security, and isolation.
1. Kernel Mode:
Privileged Execution: In kernel mode, the software has unrestricted access to all hardware resources and can execute privileged instructions. This mode allows direct manipulation of hardware components and system memory.
Critical System Functions: The operating system's core functions, such as memory management, process scheduling, hardware drivers, and interrupt handling, run in kernel mode. These functions are critical for the proper operation of the system.
Higher Privilege: Kernel mode has higher privilege and control over the system compared to user mode. It can perform tasks that could affect the stability and security of the entire system.
Protection Mechanisms: Hardware protection mechanisms, such as CPU privilege levels (e.g., rings or modes) and memory segmentation, are used to isolate kernel mode from user mode. These mechanisms prevent user mode software from directly accessing or modifying critical system resources.
2. User Mode:
Restricted Execution: In user mode, software runs in a restricted environment and does not have direct access to hardware resources. It operates through system calls and APIs provided by the operating system.
Applications and User Processes: User mode is where applications, user-level processes, and services run. Most software, including web browsers, office suites, and games, operates in user mode.
Lower Privilege: User mode has limited privilege and control over the system. It cannot directly manipulate hardware resources or execute certain privileged instructions.
Isolation and Security: User mode processes are isolated from each other and from the kernel mode. This isolation enhances security by preventing one process from interfering with or compromising the integrity of another process or the operating system.
System Calls: When user mode software needs to perform tasks that require higher privilege or access to system resources, it makes system calls to the operating system. The operating system then switches the CPU from user mode to kernel mode to execute the requested operation on behalf of the user mode software.