In computing, SUBST is a command on the DOS, IBM OS/2, Microsoft Windows and ReactOS operating systems used for substituting paths on physical and logical drives as virtual drives. Overview In MS-DOS, the SUBST command was added with the release of MS-DOS 3.1. The command is similar to floating drives, a more general concept in operating systems of Digital Research origin, including CP/M-86 2.x, Personal CP/M-86 2.x, Concurrent DOS, Multiuser DOS, System Manager 7, REAL/32, as well as DOS Plus and DR DOS (up to 6.0). DR DOS 6.0 includes an implementation of the command. The command is also available in FreeDOS and PTS-DOS. The Windows SUBST command is available in supported versions of the command line interpreter cmd.exe. In Windows NT, SUBST uses DefineDosDevice() to create the disk mappings. The JOIN command is the "opposite" of SUBST, because JOIN will take a drive letter and make it appear as a directory. Some versions of MS-DOS COMMAND.COM support the undocumented internal TRUENAME command which can display the "true name" of a file, i.e. the fully qualified name with drive, path, and extension, which is found possibly by name only via the PATH environment variable, or through SUBST, JOIN and ASSIGN filesystem mappings. Syntax This is the command syntax in Windows XP to associate a path with a drive letter: SUBST [drive1: [drive2:]path] SUBST drive1: /D Parameters drive1: – Specify a virtual drive to which to assign a path. [drive2:]path – Specify a physical drive and path to assign to a virtual drive. /D – Delete a substituted (virtual) drive. Examples Mapping a drive This means that, for example, to map C:'s root to X:, the following command would be used at the command-line interface: C:\>SUBST X: C:\ Upon doing this, a new drive called X: would appear under the My Computer virtual folder in Windows Explorer. Unmapping a drive To unmap drive X: again, the following command needs to by typed at the command prompt: C:\>SUBST X: /D Custom label A custom label can be assigned to a drive letter created in this way by way of a registry key, which can be created by renaming (select "rename" from the drive letter context menu or press ) the SUBST drive in Windows Explorer/My Computer. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\DriveIcons\M\DefaultLabel\ (DefaultValue) = Your Drive Label "M" represents the drive letter to assign a custom label to. However, labels created for SUBST drives in this manner