![cover image](https://wikiwandv2-19431.kxcdn.com/_next/image?url=https://upload.wikimedia.org/wikipedia/commons/thumb/4/45/GNU_GRUB_components.svg/640px-GNU_GRUB_components.svg.png&w=640&q=50)
Boot sector
Sector of a persistent data storage device / From Wikipedia, the free encyclopedia
This article is about the generic concept of boot sectors. For the MBR in PCs, see Master Boot Record. For the VBR in PCs, see Volume Boot Record.
A boot sector is the 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).
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/4/45/GNU_GRUB_components.svg/640px-GNU_GRUB_components.svg.png)
Usually, the first sector of the hard disk is the boot sector, regardless of sector size (512 or 4096 bytes) and partitioning flavor (MBR or 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 a firmware (e.g., the BIOS), then some code contained in the boot sector, and then, for example, an operating system, is maximal flexibility.