bootloadere

A bootloader is a small program responsible for loading an operating system during the boot process. It is executed by the system firmware after initial hardware initialization. In classic BIOS systems, the first program loaded is located in the Master Boot Record or a boot sector on the boot device; in UEFI systems, the firmware loads an EFI executable from the system partition.

The bootloader's primary tasks are to locate the OS kernel image, load it into memory, configure kernel parameters, and transfer control to the kernel. Many bootloaders support multiple operating systems or kernel options, enabling multi-boot configurations and rescue modes. They may offer features such as chain loading of other bootloaders, detection of installed kernels, and user menus.

In Linux and Unix-like systems, popular bootloaders include GRUB and Syslinux. Windows uses its own Windows Boot Manager. In embedded and consumer electronics, U-Boot (Das U-Boot) is widely used. Some bootloaders are designed to be part of the firmware (such as UEFI drivers) while others are standalone programs stored on disk or in flash.

Bootloaders can support advanced features like kernel command line parameters, initramfs loading, device initialization, and disk encryption or integrity verification. Secure boot mechanisms use cryptographic signatures to verify bootloaders and kernels before execution, helping prevent tampering.

The history of bootloaders tracks the evolution from simple MBR loaders to advanced UEFI-based systems with modular architectures. A bootloader is distinct from a kernel: it is a transitional program that prepares the system and then hands control to the kernel.