Privilege Level
How much direct access to core resources a piece of software is trusted with.
Glossary
Kernel
The protected core of the operating system, with the deepest access to memory and hardware.
In one line
The protected core of the operating system, with the deepest access to memory and hardware.
Also calledsystem corethe core
The kernel is the innermost part of the operating system. It is small. Yet it carries the highest level of trust and the most direct access to the machine, which is exactly why any code running here has to be written with unusual care. One slip can ripple outward. A single fault in this core can affect everything at once, so it is guarded far more closely than anywhere else in the system.
Some drivers sit close to the kernel for speed. Others are kept at arm's length on purpose. Where a driver runs turns out to be one of the most consequential choices made around it: closeness buys raw performance, while distance buys protection, because trouble in a far-off driver can be boxed in instead of reaching the core.
So what does the kernel actually do? Three things, mostly. It divides time between programs, manages memory, and acts as the final gatekeeper to hardware. Everything a program does eventually passes through it — even when the program never asks for the kernel by name.
Because of that central role, the kernel is kept small and conservative in spirit. The reasoning is simple. The less code that runs with such deep trust, the fewer places a serious fault can hide. This is why careful systems are slow to hand out kernel-level access, and quick to take it back.
In practice
In practice, picture the locked control room of a power plant. Most workers never enter it; they make requests from outside, and only a trusted few operate the core machinery within. The kernel is that control room for a computer, holding the deepest controls and admitting only the code that genuinely needs to be there.
