Kernel

• The core of OS.
• It directly talks to the hardware.
• Never interact with the kernel directly as a user.

In each OS

• Linux → Linux Kernel
• Windows → NT Kernel
• macOS → XNU Kernel (Mach + BSD)

Responsible for

1. Process Management
   • Create, schedule, and kill processes
   • Context switching between processes/threads
2. Memory Management
   • Allocate RAM
   • Virtual memory, paging, swapping
3. Hardware Management
   • Communicates with devices via drivers
   • Disk, keyboard, mouse, network card, GPU
4. System Calls
   • Provides APIs for programs to request services
   • Example: read file, write file, open socket

Diagram

Applications (Chrome, Java app, Docker) ↓ Shell / GUI ↓ Kernel ↓ Hardware (CPU, RAM, Disk)