Editing Boot sector (section)

{{About|the generic concept of boot sectors|the MBR in PCs|Master Boot Record|the VBR in PCs|Volume Boot Record}}
{{short description|Sector of a persistent data storage device}}
[[File:GNU GRUB components.svg|thumb|This example show various components of [[GNU GRUB]] distributed over sectors of a hard disk. When GRUB is installed on a hard disk, boot.img is written into the boot sector of that hard disk. boot.img has a size of only 446 bytes.]]

A '''boot sector''' is the [[disk sector|sector]] of a persistent [[data storage device]] (e.g., [[hard disk]], [[floppy disk]], [[optical disc]], etc.) which contains [[machine code]] to be loaded into [[random-access memory]] (RAM) and then executed by a [[computer system]]'s built-in [[firmware]] (e.g., the [[BIOS]]).

Usually, the first sector of the hard disk is the boot sector, regardless of sector size (512 or 4096 bytes) and partitioning flavor ([[Master boot record|MBR]] or [[GUID Partition Table|GPT]]).

The purpose of defining one particular sector as the ''boot sector'' is inter-operability between firmware and various operating systems.

The purpose of chain-loading, first firmware (e.g., the BIOS), then code in the boot sector, and then, for example, an operating system, is maximal flexibility.