How is the operating system startup initiated when turning on the computer?

The process of system startup involves several stages:

1. Power on and POST (Power-On Self Test):

   • Hardware check of main components (memory, CPU, devices).

2. Bootloader loading:

   • BIOS or UEFI searches for a boot device (hard drive, SSD, USB, etc.).
   • Reads the first sector of the boot device (MBR or GPT) and loads the bootloader.

3. OS loader:

   • The loader (e.g., GRUB for Linux) loads the kernel into memory.

4. Kernel initialization:

   • The OS kernel initializes hardware, mounts the root filesystem.

5. System services and user processes:

   • init system (systemd, SysVinit, etc.) starts other services and user interface.

Thus, the startup process is a sequence from hardware testing to kernel loading and system services startup.