1. Shell

• Definition: The shell is the user interface for interacting with the operating system.
• Role: It takes commands from the user (text commands in CLI like bash, or graphical ones in GUI shells like Windows Explorer) and passes them to the OS to execute.
• Types:
  • Command-line shell (e.g., Bash, Zsh, PowerShell)
  • Graphical shell (e.g., Windows desktop, GNOME on Linux)
• Analogy: Think of it as the “translator” that lets a human talk to the computer.

2. Kernel

• Definition: The kernel is the core part of the operating system that directly interacts with hardware.
• Role:
  • Manages CPU, memory, and devices.
  • Provides system calls that applications use to request resources.
• Types:
  • Monolithic kernel (Linux) — big, everything runs inside it.
  • Microkernel (Minix, QNX) — minimal core, with services run outside.
• Analogy: The kernel is the “engine” of the operating system. It does the heavy lifting.

3. BIOS (Basic Input/Output System)

• Definition: BIOS is firmware stored on the motherboard that initializes hardware when you power on your computer.
• Role:
  • Performs POST (Power-On Self Test).
  • Loads the bootloader/OS from storage.
  • Provides basic routines for input/output (keyboard, display, disk) before the OS takes over.
• Modern Equivalent: UEFI (Unified Extensible Firmware Interface) has mostly replaced BIOS in modern PCs.
• Analogy: The BIOS is like the “ignition system” of a car — it starts everything and hands over control to the main system.

4. Driver

• Definition: A driver is a small piece of software that allows the operating system to communicate with hardware.