Extent (file systems)

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An extent is a contiguous area of storage in a computer file system, reserved for a file. When a process creates a file, file system management software allocates a whole extent. When writing to the file again, possibly after doing other write operations, the data continues where the previous write left off. This reduces or eliminates file fragmentation and possibly file scattering.

An extent-based file system, which addresses storage via extents rather than in separate blocks, does not have to limit each file to a single, contiguous extent.


The following systems support extents:

As a similar design, the CP/M file system uses extents as well, but those do not correspond to the definition given above. CP/M's extents appear contiguously as a single block in the combined directory/allocation table, and they do not necessarily correspond to a contiguous data-area on disk.

See also[edit]


  1. ^ "Understanding Pages and Extents". msdn.microsoft.com. Retrieved 2014-08-14. 

External links[edit]