käynnistyslataajat

Käynnistyslataaja, or bootloader in English, is a special program that runs when a computer or other device is first turned on. Its primary role is to load the operating system into the computer's memory. Before the operating system can start, the processor needs instructions on how to begin its operations, and this is where the bootloader comes in.

When a device powers up, it typically executes firmware or BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface). This initial firmware performs hardware checks and then looks for a bootable device, such as a hard drive, SSD, or USB drive. Once a bootable device is found, the firmware locates and loads the bootloader from a designated area on that device, often called the Master Boot Record (MBR) or the EFI System Partition (ESP).

The bootloader's task is then to find the kernel of the operating system and load it into RAM. It might also present a boot menu if multiple operating systems are installed on the device, allowing the user to choose which one to start. After loading the kernel and any necessary initial system files, the bootloader hands over control to the operating system, which then continues the startup process. Different operating systems and hardware architectures often use different bootloaders, such as GRUB for Linux systems or the Windows Boot Manager for Windows.