käynnistyslataajissa

Käynnistyslataajat, or bootloaders in English, are essential software programs that run when a computer or device is first powered on. Their primary function is to load the operating system into the computer's memory so that the system can start functioning. Without a bootloader, the computer would not know how to access or initiate the operating system.

The process typically begins with the BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface), which is stored on a chip on the motherboard. This firmware performs a Power-On Self-Test (POST) to check hardware components. After POST, the BIOS/UEFI looks for a bootable device, usually a hard drive, SSD, USB drive, or CD/DVD. Once a bootable device is found, the BIOS/UEFI locates the bootloader stored in a specific sector of that device, often called the Master Boot Record (MBR) or a dedicated EFI System Partition.

The bootloader then takes over. It reads its configuration and presents options to the user, such as choosing between different operating systems if multiple are installed. After the user makes a selection (or if there's only one option), the bootloader loads the kernel of the chosen operating system from the storage device into RAM. Finally, control is handed over to the operating system kernel, which continues the boot process and initializes the rest of the system. Popular examples include GRUB (GRand Unified Bootloader) and LILO (LInux LOader) for Linux systems, and the Windows Boot Manager for Microsoft Windows.