Boot Sector Definition

A boot sector is a region (typically the first 512 bytes) of a hard disk drive (HDD), floppy disk or other data storage device, or of a partition (i.e., a logically independent section of a HDD), that contains information for booting (i.e., starting up) an operating system that is stored on that device or partition.

The term is usually used to refer to the master boot record (MBR), which occupies the first sector of a HDD, although each partition can have a boot sector. The MBR is a small program that is executed when a computer begins to boot in order to find the operating system and copy parts of it, and particularly its kernel (i.e., the core of the operating system), from a storage device, typically the HDD, into memory so that it can be directly accessed by the central processing unit (CPU).

A sector is a segment of a track on a magnetic disk (i.e., a floppy disk or a platter in a HDD). It generally contains 512 bytes and is the smallest unit of data that can be accessed by a disk drive (although software makes it possible to access individual bytes and even individual bits). A track is any of the concentric circles on the magnetic media on a disk over which one magnetic head (i.e., a high-precision electromagnet used for reading and writing data on the disk) passes while the head is stationary but the disk is spinning.

Created April 14, 2006.
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