(This was the era of 8-inch floppy disks, where such small namespaces did not impose practical constraints.) This usage was influenced by the device prefixes used in Digital Equipment Corporation's (DEC) TOPS-10 operating system. Early versions of CP/M (and other microcomputer operating systems) implemented a flat file system on each disk drive, where a complete file reference consists of a drive letter, a colon, a filename (up to eight characters), a dot, and a filetype (three characters) for instance A:README.TXT. CP/CMS inspired numerous other operating systems, including the CP/M microcomputer operating system, which uses a drive letter to specify a physical storage device.Minidisks can correspond to physical disk drives, but more typically refer to logical drives, which are mapped automatically onto shared devices by the operating system as sets of virtual cylinders. A full file reference ( pathname in today's parlance) consists of a filename, a filetype, and a disk letter called a filemode (e.g. CP/CMS uses drive letters to identify minidisks attached to a user session. The concept evolved through several steps: The concept of drive letters, as used today, presumably owes its origins to IBM's VM family of operating systems, dating back to CP/CMS in 1967 (and its research predecessor CP-40), by way of Digital Research's (DRI) CP/M. 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). 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. In computer data storage, drive letter assignment is the process of assigning alphabetical identifiers to volumes. File Manager displaying the contents of drive C. MS-DOS command prompt with drive letter C as part of the current working directory. Alphabetical assignment to logical drives on computers (e.g., C:\)
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