OS//OS kernel

The OS kernel is the privileged core of an operating system, the one program that runs with full hardware access and decides, on behalf of every other program, who gets the CPU, which memory, which files and which devices. Applications never touch the hardware directly: they ask the kernel through a syscall, and the kernel either does the work or refuses.

The OS kernel is the privileged core of an operating system, the one program that runs with full hardware access and decides, on behalf of every other program, who gets the CPU, which memory, which files and which devices. Applications never touch the hardware directly: they ask the kernel through a syscall, and the kernel either does the work or refuses.

It lives in kernel space, a protected region where a fault takes down the whole machine, while processes run in user space, where a fault kills only the culprit. That split is the reason one crashing browser tab does not reboot the laptop.

Its core jobs are four: scheduling processes and threads on the cores, managing virtual memory, running the file systems, and driving devices through their drivers (network cards, disks, the serial port a Modbus adapter hangs on). Interrupts from those devices land in the kernel first.

It is also the enforcement point for isolation. Linux builds containers out of kernel features (namespaces narrow what a process can see, control groups cap what it can consume, syscall filters restrict what it may ask for), so containers on one host all share its kernel. A virtual machine instead boots a kernel of its own on a hypervisor, heavier but separated at a lower level.

Its scheduling is general-purpose by default: it optimises fairness and throughput, and a thread can wait milliseconds for its turn. Hard timing guarantees need a real-time operating system or a real-time patch, which is why a motor loop does not run on a plain desktop kernel.

The kernel is the building's management office.

Tenants never enter the boiler room; they fill in a request, and the office decides whether, when and how.

The word kernel also names unrelated things (a GPU compute kernel, the kernel of a matrix): here it is only the core of the OS. How the kernel's mediation shows up in practice is developed in OS process.