A volume boot record (VBR) (also known as a volume boot sector, a partition boot record or a partition boot sector) is a type of boot sector introduced by the IBM Personal Computer. It may be found on a partitioned data storage device such as a hard disk, or an unpartitioned device such as a floppy disk, and contains machine code for bootstrapping programs (usually, but not necessarily, operating systems) stored in other parts of the device. On non-partitioned storage devices, it is the first sector of the device. On partitioned devices, it is the first sector of an individual partition on the device, with the first sector of the entire device being a master boot record (MBR) containing the partition table.
The code in volume boot records is invoked either directly by the machine's firmware or indirectly by code in the master boot record or a boot manager. Code in the MBR and VBR is in essence loaded the same way.
Invoking a VBR via a boot manager is known as chain loading. Some dual boot systems, such as NTLDR (the boot loader for all releases of Microsoft's Windows NT-derived operating systems up to and including Windows XP and Windows Server 2003), take copies of the bootstrap code that individual operating systems install into a single partition's VBR and store them in disc files, loading the relevant VBR content from file after the boot loader has asked the user which operating system to bootstrap. In Windows Vista, Windows Server 2008 and newer versions, NTLDR was replaced; the boot loader functionality is instead provided by two new components: winload.exe and the Windows Boot Manager.
In file systems such as FAT12 (except for in DOS 1.x), FAT16, FAT32, HPFS and NTFS, the VBR also contains a BIOS Parameter Block (BPB) that specifies the location and layout of the principal on-disc data structures for the file system. (A detailed discussion of the sector layout of FAT VBRs, the various FAT BPB versions and their entries can be found in the FAT article.)
Famous quotes containing the words volume, boot and/or record:
“We are too civil to books. For a few golden sentences we will turn over and actually read a volume of four or five hundred pages.”
—Ralph Waldo Emerson (1803–1882)
“The best quality tea must have creases like the leathern boot of Tartar horsemen, curl like the dewlap of a mighty bullock, unfold like a mist rising out of a ravine, gleam like a lake touched by a zephyr, and be wet and soft like a fine earth newly swept by rain.”
—Lu Yu (d. 804)
“Unlike Boswell, whose Journals record a long and unrewarded search for a self, Johnson possessed a formidable one. His life in London—he arrived twenty-five years earlier than Boswell—turned out to be a long defense of the values of Augustan humanism against the pressures of other possibilities. In contrast to Boswell, Johnson possesses an identity not because he has gone in search of one, but because of his allegiance to a set of assumptions that he regards as objectively true.”
—Jeffrey Hart (b. 1930)