What is a bootloader?
A bootloader is a small software component that starts an operating-system kernel or the next stage of startup.
How it works and where it is used
After power-on, firmware initializes hardware; the bootloader finds system files and hands over control. PCs, phones and embedded systems use different chains. A menu for several operating systems may live here. Boot failure can also stem from disk, partition or boot configuration, not only the OS.
Limits, safety and selection criteria
Secure boot chains aim to verify authorized code at each stage, with keys and signatures differing by device. Prepare recovery media and backups before editing boot partitions. A mistaken repair command can render another installed system unbootable. Every stage in the startup chain must know where to load the next. UEFI boot entries and the EFI system partition differ from legacy BIOS arrangements. Copying only operating-system files to another drive may not be enough; boot partitions can matter too. Major updates may change the menu on a dual-boot computer. During repair, verify the selected drive and partition names twice to avoid changing boot records on the wrong disk. Keep encryption recovery credentials separate from the machine before experimenting with boot settings.