Volume Boot Record

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The volume boot record ( VBR short ) are the first sectors of a partition of a storage medium such as a hard disk, in a BIOS -based computer with one or more partitions within a File Allocation Table file system. A VBR can (depending on the support provided by the file system) differ in size, but at least is the first sector available, which includes information received from the Master Boot Record (MBR ) can be evaluated when the computer boots. This article describes a three -sector VBR.

Construction of a VBR

Sector 0 of the VBR

The table below shows the structure of the sector 0 of a VBR dar. The individual function bytes are counted, as an offset from the beginning of VBR.

15:8 .. reserved 7 .. 0 => FAT is mirrored at runtime into all FATs other. 1 => only one FAT is active. 6:4 .. reserved. 3-0 .. number of the active FAT ( 0 based) if mirroring is not enabled ( see bit 7).

Sector 1 of the VBR

The following sector contains almost no information about the partition. The first 4 bytes ( starting at offset 0x200 ) 0x52 0x52 0x61 0x41 in principle or " rraa " and mark the beginning of the VBR extension. A similar entry is found offset 0x3EA to 0x3E7. Here is the beginning of the data for all of the free cluster (offset 0x3E8 to 0x3EB ) and Closest -availability cluster is marked (offset 0x3EC to 0x3EF ). Since a FAT can become very large well, this information serves as a guide for the FAT driver, where you can begin looking for available memory. Also, sector 1 of the VBR ends with the magic number 0x55 0xAA in offset 0x3FE to 0x3FF.

Sector 2 of the VBR

Sector 2 of the VBR has no use for now. It provides extra storage for boot code available for the event that sector 0 is not enough had space for the boot code. If the entire boot code already in sector 0, sector 2 remains empty except for the last two bytes in offset 0x5FE and 0x5FF, which in turn contain the magic number 0x55 0xAA.

Copy of the VBR

Under the FAT32 file system from all three sectors of the VBR is created a backup copy in the sectors 6-8. These can be used in case of any damage to the VBR for recovery. Consistent formatting programs overwrite your backup copy is usually not so purely a format a partition and the associated new application of a FAT far from guaranteed safe removal of all existing data on the partition.