Kernel space and User space

kernel space and user space

A conventional computer operating system usually segregates virtual memory into kernel space and user space. Kernel space is strictly reserved for running the kernel, kernel extensions, and most device drivers. In contrast, user space is the memory area where all user mode applications work and this memory can be swapped out when necessary.

The really simplified answer is that the kernel runs in kernel space, and normal programs run in user space. User space is basically a form of sand-boxing -- it restricts user programs so they can't mess with memory (and other resources) owned by other programs or by the OS kernel. This limits (but usually doesn't entirely eliminate) their ability to do bad things like crashing the machine.

The kernel is the core of the operating system. It normally has full access to all memory and machine hardware (and everything else on the machine. To keep the machine as stable as possible, you normally want only the most trusted, well-tested code to run in kernel mode/kernel space.

The stack is just another part of memory, so naturally it's segregated right along with the rest of memory.

The random access memory (RAM) can be divided into two distinct regions namely - the kernel space and the user space.

The kernel runs in the part of memory entitled to it. This part of memory cannot be accessed directly by the processes of the normal users, while as the kernel can access all parts of the memory. To access some part of the kernel, the user processes have to use the predefined system calls i.e. open, read,write etc. Also, the C library functions like printf call the system call write in turn.

The system calls act as an interface between the user processes and the kernel processes. The access rights are placed on the kernel space in order to stop the users from messing up with the kernel, unknowingly.

So, when a system call occurs, a software interrupt is sent to the kernel. The CPU may hand over the control temporarily to the associated interrupt handler routine. The kernel process which was halted by the interrupt resumes after the interrupt handler routine finishes its job.