Käynnistyskoodi

Käynnistyskoodi refers to the initial set of instructions that a computer executes when it is powered on or reset. This code is typically stored in non-volatile memory, such as a ROM (Read-Only Memory) or flash memory chip, on the motherboard. Its primary purpose is to initialize the system hardware, perform basic checks, and then load the operating system or another bootloader from a storage device.

The process begins with the BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface) firmware, which contains the initial käynnistyskoodi. This firmware tests essential hardware components, including the CPU, RAM, and graphics card, through a Power-On Self-Test (POST). Once the POST is complete, the käynnistyskoodi looks for a bootable device, which could be a hard drive, SSD, USB drive, or network interface.

The firmware then reads the Master Boot Record (MBR) or GUID Partition Table (GPT) from the selected bootable device. This sector contains information about the partitions on the drive and a small bootloader program. This bootloader is the next stage of the käynnistyskoodi process. It is responsible for loading the main operating system kernel into memory and transferring control to it, allowing the operating system to take over and complete the startup sequence. The specific implementation and sequence of käynnistyskoodi can vary between different computer architectures and operating systems.