High Quality Content by WIKIPEDIA articles! Drive letter assignment is the process of assigning alphabetical identifiers to physical or logical disk drives or partitions (drive volumes) in the root filesystem namespace; this usage is now mostly found in Microsoft operating systems. Unlike the concept of UNIX mount points, where volumes are named and located arbitrarily in a single hierarchical namespace, drive letter assignment allows multiple highest-level namespaces. Drive letter assignment is thus a process of using letters to name the roots of the "forest" representing the file system; each volume holds an independent "tree" (or, for non-hierarchical file systems, an independent list of files).