BSD disklabel

In BSD-derived computer operating systems (including NetBSD, OpenBSD, FreeBSD and DragonFly BSD) and in related operating systems such as SunOS, a disklabel is a record stored on a data storage device such as a hard disk that contains information about the location of the partitions on the disk. Disklabels were introduced in the 4.3BSD-Tahoe release. Disklabels are usually edited using the disklabel utility. In later versions of FreeBSD, this was renamed as bsdlabel.

Traditionally, the disklabel was the first sector of the disk. However, this system only works when the only operating systems that access the disk are Unix systems that comprehend disklabels. In the world of IBM PC compatibles, disks are usually partitioned using the PC BIOS's master boot record (MBR) Partition Table scheme instead, and the BSD partitioning scheme is nested within a single, primary, MBR partition (just as the "extended" partitioning scheme is nested within a single primary partition with extended boot records). Sometimes (particularly in FreeBSD), the primary MBR partitions are referred to as slices and the subdivisions of a primary MBR partition (for the nested BSD partitioning scheme) that are described by its disklabel are called partitions. The BSD disklabel is contained within the volume boot record of its primary MBR partition.

The MBR partition IDs for primary partitions that are subdivided using BSD disklabels are A5h (386BSD and FreeBSD), A6h (OpenBSD), and A9h (NetBSD).

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