Käynnistymisprosessi

Käynnistymisprosessi, often referred to as the boot process, describes the sequence of operations a computer performs when it is turned on until it becomes ready to accept user commands. This process is fundamental to the functioning of any computer system.

Upon receiving power, the system's central processing unit (CPU) executes a small, pre-programmed piece of firmware, typically stored in read-only memory (ROM) or flash memory. This initial code is known as the Basic Input/Output System (BIOS) or Unified Extensible Firmware Interface (UEFI) on modern systems. The primary role of the BIOS/UEFI is to initialize the hardware components, such as the CPU, memory, and basic input/output devices, and then to locate and load the operating system.

The BIOS/UEFI performs a Power-On Self-Test (POST) to check the integrity of essential hardware. If POST is successful, the firmware then searches for a bootable device, which could be a hard drive, solid-state drive, USB drive, or network connection, according to a predefined boot order. Once a bootable device is found, the BIOS/UEFI loads the first sector of that device, known as the boot sector or Master Boot Record (MBR) / GUID Partition Table (GPT), into memory.

This boot sector contains instructions to load the operating system's bootloader. The bootloader is a small program responsible for loading the main operating system kernel into memory. The kernel, the core of the operating system, then takes control, initializes device drivers, sets up memory management, and starts essential system processes, eventually presenting the user interface.