Partition type

The partition type (or partition ID) in a partition's entry in the partition table inside a master boot record (MBR) is a byte value intended to specify the file system the partition contains and/or to flag special access methods used to access these partitions (f.e. special CHS mappings, LBA access, logical mapped geometries, special driver access, hidden partitions, secured or encrypted file systems, etc.).

Lists of assigned partition types to be used in the partition table in the MBR were originally maintained by IBM and Microsoft internally. When the market of PC operating systems and disk tools grew and liberated, other vendors had a need to assign special partition types to their products as well. As Microsoft neither documented all partition types already assigned by them nor wanted to maintain foreign assignments, third parties started to simply assign partition types on their own behalf in a mostly uncoordinated trial-and-error manner. This led to various conflictive double-assignments sometimes causing severe compatibility problems between certain products.

Several industry experts including Hale Landis, Ralf Brown, Matthias Paul, and Andries E. Brouwer in the 1990s started to research partition types and published (and later synchronized) partition type lists in order to help document the industry de facto standard and thereby reduce the risk of further conflicts. Some of them also actively helped to maintain software dealing with partitions to work with the updated lists, indicated conflicts, devised additional detection methods and work-arounds for vendors, or engaged in coordinating new non-conflictive partition type assignments as well.

While not officially maintained,new assignments should be coordinated, in particular any new temporary partition type assignments for local or experimental projects can utilize type 7Fh in order to avoid conflicts with already assigned types. This type was specially reserved for individual use as part of the Alternative OS Development Partition Standard (AODPS) initiative since 2002.

It is up to an operating system's boot loader or kernel how to interpret the value. So the table specifies which operating systems or disk-related products originally introduced an ID and what file system or special partition type they mapped it to. Partitions with partition types unknown to the software should be treated as reserved but occupied disk storage space, which should not be dealt with by the software, except for in FDISK-like tools.

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