The boot chain is the ordered set of low-level components that bring a device from power-on to the main operating system. It usually includes firmware, a bootloader, hardware initialization code, and sometimes signed verification steps before the kernel starts. Each stage hands control to the next, so a weakness early in the chain can affect everything that follows.
In cyber security, the boot chain matters because it is a high-value target for persistence and trust. Attackers who modify firmware or a bootloader can survive OS reinstallations, hide from many endpoint tools, or disable security checks. Defenders harden the boot chain with secure boot, measured boot, signed images, hardware root of trust, and firmware integrity checks. In embedded systems and consoles, custom hardware and vendor-specific loaders make boot-chain work especially important during ports, recovery, and incident response.