Operating System

What a system booting ? Explain

The boot process typically consists of several stages:

  • Power-On Self-Test (POST):
    • When the computer is powered on, the hardware components undergo a self-diagnostic test known as the POST.
    • The POST checks various hardware components such as the CPU, memory (RAM), storage devices (hard drives, SSDs), graphics card, and other peripherals to ensure they are functioning correctly.
    • If the POST detects any errors or issues with the hardware, it may display error messages or emit audible alerts to notify the user.
  • Bootstrap Loader:
    • After the POST completes successfully, the system’s firmware (BIOS or UEFI) locates and loads the bootstrap loader, which is typically stored in non-volatile memory (e.g., ROM or EEPROM) on the motherboard or storage device.
    • The bootstrap loader is a small program that initializes the computer’s hardware and locates the operating system kernel to load into memory.
    • On systems with BIOS firmware, the bootstrap loader may search for the boot sector of the designated boot device (e.g., hard drive, SSD) based on the boot order configured in the BIOS settings.
    • On systems with UEFI firmware, the bootstrap loader interacts with the UEFI firmware and the EFI System Partition (ESP) to locate and load the bootloader.
  • Bootloader:
    • The bootloader is a small program responsible for loading the operating system kernel into memory and initializing the operating system environment.
    • Depending on the system configuration, the bootloader may present a menu allowing the user to choose which operating system or boot options to load.
    • Common bootloaders include GRUB (GRand Unified Bootloader) for Linux-based systems and the Windows Boot Manager for Windows-based systems.
  • Operating System Kernel Loading:
    • Once the bootloader identifies the location of the operating system kernel, it loads the kernel into memory.
    • The kernel is the core component of the operating system responsible for managing system resources, providing essential services, and coordinating system operations.
  • Initialization and System Setup:
    • After the kernel is loaded into memory, it begins the initialization process.
    • During initialization, the kernel initializes hardware devices, mounts the filesystem, starts essential system services, and sets up the user environment.
    • Once initialization is complete, the system is ready for user interaction, and the user may log in and start using the computer.

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