The booting process refers to the sequence of steps a computer system follows to load the operating system into memory and start functioning. It is a critical component of system startup.
- Cold Boot (Hard Boot):
- Starting the computer from a completely powered-off state.
- Warm Boot (Soft Boot):
- Restarting the computer without turning off the power (e.g., using Ctrl+Alt+Del or Restart).
- Power is supplied to the motherboard.
- Power Supply Unit (PSU) checks voltage levels (Power Good signal).
- CPU is reset and takes control.
- Performed by BIOS/UEFI.
- Checks:
- RAM
- CPU
- Keyboard
- Storage devices
- Errors are reported via beep codes or messages.
- BIOS/UEFI is firmware stored on the motherboard.
- Looks for a bootable device based on boot priority.
- Loads the bootloader from the MBR/GPT.
- Examples: GRUB (Linux), Windows Boot Manager.
- Responsibilities:
- Load the OS kernel.
- Pass control to the kernel.
- GRUB may offer a menu to select OS/version.
- The kernel is loaded into memory.
- Initializes:
- Memory management
- Device drivers
- File system
- Launches the first user-space program (init or systemd).
- Initializes system services and targets.
- GUI: GDM, LightDM, SDDM
- CLI: login prompt
- Accepts user credentials and starts user session.
| Component | Role |
|---|---|
| BIOS/UEFI | Initializes hardware, locates and runs the bootloader |
| Bootloader | Loads the kernel into memory |
| Kernel | Core of the OS, manages hardware and system processes |
| Init/Systemd | Initializes and manages services and user-space processes |
| Shell/Desktop | Provides user interface (CLI/GUI) |
-
MBR (Master Boot Record):
- Found on first sector of bootable disk.
- Contains bootloader and partition table.
-
UEFI vs BIOS:
- UEFI is modern, supports larger drives, secure boot.
- BIOS is older and being phased out.
-
Dual Boot:
- Multiple OS installed.
- Bootloader presents a menu to choose.
