What Is a Volume Boot Record?

Definition of VBR (Volume Boot Record) & How to Repair a Volume Boot Record

A volume boot record, frequently called a partition boot sector, is a type of boot sector, stored on a particular partition on a hard disk drive or other storage device, that contains the necessary computer code to start the boot process.

One component of the volume boot record that's specific to the operating system or program itself, and is what's used to load the OS or software, is called the volume boot code. The other is the disk parameter block, or media parameter block, which contains information about the volume like its label, size, clustered sector count, serial number, and more.

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A volume boot record is commonly abbreviated as VBR, but is also sometimes referred to as a partition boot sector, partition boot record, boot block, and volume boot sector.

VBR is also an acronym for variable bit rate, which has nothing to do with a boot sector but instead refers to the number of bits processed over time. It's the opposite of constant bit rate or CBR. See CBR vs VBR Encoding for more information.

Repairing a Volume Boot Record

If the volume boot code becomes corrupted or configured in some incorrect way, you can repair it by writing a new copy of the boot code to the system partition.

The steps involved in writing a new volume boot code depend on what ​version of Windows you're using:

More Information on a Volume Boot Record

The volume boot record is created when a partition is formatted. It resides on the first sector of the partition. However, if the device isn't partitioned, like if you're dealing with a floppy disk, then the volume boot record is on the first sector of the whole device.

A master boot record is another type of boot sector. If a device has one or more partitions, the master boot record is on the first sector of the whole device.

All disks only have one master boot record, but can have multiple volume boot records because of the simple fact that a storage device can hold multiple partitions, which each have their own volume boot record.

The computer code that's stored in the volume boot record is either started up by the BIOS, master boot record, or a boot manager. If a boot manager is used to call the volume boot record, it's called chain loading.

NTLDR is the boot loader for some versions of Windows (XP and older). If you have more than one operating system installed to the hard drive, it takes specific code relevant to the different operating systems and puts them together into one volume boot record so that, before any OS starts up, you can choose which one to boot to. Newer versions of Windows have replaced NTLDR with BOOTMGR and winload.exe.

Also in the volume boot record is information regarding the file system of the partition, like if it's NTFS or FAT, as well as where the MFT and MFT Mirror is (if the partition is formatted in NTFS).

A volume boot record is a common target for viruses since its code starts even before the operating system can load, and it does so automatically without any user intervention. 

FAQ
  • What's the difference between MBR and VBR?

    A master boot record (MBR) is created when a hard drive is partitioned, but it's not contained within a partition. Its job is to find the partition with the VBR so that the boot process can begin. Unlike the VBR, the MBR is not specific to any operating system.

  • What Is Windows Boot Manager (BOOTMGR)?

    Windows BOOTMGR is the default boot manager for Windows 10, Windows 8, Windows 7, and Windows Vista. It loads the volume boot code from the VBR so that Windows can start up.

  • How do I deal with boot sector viruses?

    Use antivirus software or the DOS SYS command to repair boot sector viruses, then boot from a known clean system disk. To avoid boot sector viruses, remove all external media (i.e. USB drives) before shutting down your computer.

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