Bootsektors

Bootsektors are the initial sectors on a bootable data storage device that contain the bootstrap program responsible for starting an operating system. In technical discussions, the term is used to describe the low-level code executed by firmware during power-on or reset, with the primary role of loading the operating system into memory. While the exact contents vary by filesystem and platform, bootsektors share the function of transitioning from firmware control to the OS proper.

On traditional BIOS-based PC systems, the first 512-byte boot sector, often called the master boot sector, contains bootstrap code, a small partition table, and a signature. The bootstrap code typically loads a second-stage bootloader from an active partition, which in turn locates and loads the operating system kernel. In some configurations, the boot sector directly loads an operating system image. In other environments, such as removable drives, the boot sector may be tailored to specific filesystems or bootloaders (for example, GRUB, NTLDR, or LILO).

With the advent of GUID Partition Table (GPT) and the UEFI firmware interface, the role of a traditional boot sector has diminished. UEFI systems rely on a separate EFI System Partition containing boot application files with .efi extensions, and do not require the 512-byte boot sector in the same way as BIOS systems. However, the concept persists in embedded devices and legacy or multiboot setups, where a bootsektor may still exist as a fallback mechanism or in compatibility modes.

Bootsektors are a notable security concern because compromised boot code can subvert the entire system. Protective measures include digital signing of bootloaders, Secure Boot, firmware verification, and regular updates to prevent bootkits and related threats.

See also: boot sector, Master Boot Record, Volume Boot Record, GRUB, UEFI, Secure Boot.