Kernel
The privileged core of an operating system that enforces isolation and controls hardware via system calls, scheduling, memory management, and drivers.
Definition
The kernel is the privileged core of the operating system. It has the authority to directly control hardware and enforce global safety rules.
Most application code does not run in the kernel. It runs in user space.
What makes it “privileged”
CPUs provide privilege modes (conceptually: “kernel mode” vs “user mode”). In kernel mode, code can execute instructions that user-space code is not allowed to execute: configure memory mappings, talk to device drivers, manage interrupts, and so on.
That privilege is why the kernel is treated as a trusted computing base: if it’s compromised, all isolation guarantees are in trouble.
What the kernel is responsible for (typical list)
- process and thread scheduling (who gets CPU time)
- memory management (virtual memory, paging, protection)
- device drivers and I/O stacks (disks, network interfaces, etc.)
- enforcing permissions and boundaries (isolation)
- exposing a stable API to user space via system calls
How user space uses the kernel
User-space programs request privileged operations through system calls. The call itself is a controlled boundary crossing: the kernel validates the request and either performs it or denies it with an error.