käynnistysprosessissa

Käynnistysprosessi, or boot process, refers to the sequence of operations that a computer performs when it is turned on. This process loads the operating system into the computer's main memory, making it ready for use. The exact steps can vary slightly depending on the computer's hardware and the operating system installed, but the general principle remains the same.

When a computer is powered on, the Central Processing Unit (CPU) begins executing instructions from a special firmware, typically the BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface), stored on a chip on the motherboard. This firmware performs a Power-On Self-Test (POST) to check that essential hardware components, such as the CPU, RAM, and graphics card, are functioning correctly.

Following a successful POST, the firmware identifies the boot device, which is usually a hard drive, solid-state drive, or USB drive containing the operating system. It then loads the boot loader, a small program responsible for initiating the operating system's loading sequence. The boot loader finds the operating system kernel and loads it into RAM. Once the kernel is in memory, it takes control of the system and continues the boot process, initializing various hardware devices, loading necessary drivers, and starting essential system services. Finally, the operating system's user interface is displayed, and the computer is ready for user interaction.