A computer has two main modes: user mode and kernel mode. The computer is in user mode when using programs like word processors or games.
But when these programs need to communicate with the hardware (like the screen or keyboard), the computer switches to kernel mode, where the core part of the computer, called the kernel, takes charge.
While using your computer, it often switches between these modes.
The operating system performs its most important tasks in kernel mode. The main difference between User Mode and Kernel Mode is that User Mode is where applications run, while Kernel Mode is a privileged mode the computer enters when it needs to access hardware resources.
What is User Mode?
When a computer program is running, like Excel, PowerPoint, reading a PDF, or browsing the internet, it’s in user mode. In this mode, these programs do their usual tasks. However, if any of these programs need to use hardware resources, they must send a request to the “kernel.” User mode has limited access to hardware, so it’s often referred to as a “less privileged mode,” “slave mode,” or “restricted mode.”
In user mode, each process has its own separate address space and cannot access the address space reserved for the kernel. This means that if one process fails or encounters a problem, it won’t impact the entire operating system. When there’s an interrupt, it only affects the specific process that triggered it, not the entire system.
What is Kernel Mode?
A kernel is a special software program responsible for managing and controlling the hardware components of a computer system. It acts as an intermediary or middleman between the hardware and the application software or user programs. Kernel mode is a special mode reserved for the operating system’s most trusted and low-level functions.
When a process is running in user mode and needs hardware resources like RAM or a printer, the process has to request the kernel. These requests are made using system calls. This request causes the computer to switch from user mode to Kernel Mode.
Once the task is done, the mode switches back from kernel mode to user mode. This switch is known as “context switching.” Kernel mode is sometimes called system mode or privileged mode. It’s important to note that not all processes can run in kernel mode because if one process fails, it could potentially affect the entire operating system.
System calls come in various types to help manage different aspects of a computer’s operations:
- Process Control System Calls: These system calls handle the creation and termination of processes. They allow you to start and stop programs.
- File Management System Calls: These deal with files. They enable processes to read from, write to, create, delete, open, and close files on the computer.
- Device Management System Calls: These system calls are used for interacting with hardware devices. They request access to devices, release them when done, and can also retrieve or modify device attributes.
- Information Maintenance System Calls: These help maintain system information such as the date, time, and other system-related data.
- Communication System Calls: These are used when processes need to communicate with each other. They can establish or close connections between processes, allowing them to send and receive status information.
Difference Between User Mode and Kernel Mode
|Aspect||User Mode||Kernel Mode|
|Access to Resources||In user mode, programs do not have direct access to system resources. To access these resources, a system call must be made.||In kernel mode, programs have direct and unrestricted access to system resources.|
|Interruptions||In user mode, if an interrupt occurs, it typically affects only the single process that triggered it, reducing the likelihood of a system-wide crash.||In kernel mode, if an interrupt occurs, the entire operating system might go down, leading to a system crash.|
|Modes||User mode is also known as the unprivileged mode, restricted mode, or slave mode.||Kernel mode is also known as privileged mode or system mode.|
|Virtual Address Space||In user mode, each process gets its own separate virtual address space, isolating them from one another.||In kernel mode, all processes share a single virtual address space, allowing them to access the same memory locations.|
|Level of Privilege||In user mode, applications have fewer privileges and are restricted in their ability to directly access and control system resources.||In kernel mode, applications have more privileges compared to user mode. They can access and control system resources without restrictions.|
|Restrictions||In user mode, restrictions are imposed, and access to kernel programs and resources is mediated through system calls.||In kernel mode, there are fewer restrictions as it can access both user and kernel programs without limitations.|
|Mode Bit Value||The mode bit for user-mode is usually set to 1.||The mode bit for kernel-mode is typically set to 0.|
|Memory References||In user mode, programs can only make references to memory allocated for user mode, ensuring separation from kernel memory.||In kernel mode, programs can reference both user and kernel memory areas, giving them broader memory access.|
|System Crash||A system crash in user mode is less critical and can often be recovered by resuming the user session or restarting the affected application.||A system crash in kernel mode is severe and can have complex consequences, potentially requiring system recovery measures.|
|Access||User programs can access and execute in user mode for a given system, but their actions are subject to restrictions.||In kernel mode, only essential and trusted functionality is permitted to operate, making it a powerful and significant mode.|
|Functionality||User mode is a standard viewing mode where programs cannot execute on their own or reference arbitrary memory blocks; they require an Application Protocol Interface (API) to perform these tasks.||Kernel mode can refer to any memory block in the system, direct the CPU for the execution of instructions, and perform critical system functions.|