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Drive letter assignment
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== {{anchor|Memory drive}}Common assignments == Applying the scheme discussed above on a fairly modern Windows-based system typically results in the following drive letter assignments: *'''A:''' β [[Floppy disk drive]]s, {{frac|3|1|2}}β³ or {{frac|5|1|4}}β³, and possibly other types of disk drives, if present. *'''B:''' β Reserved for a second floppy drive (that was present on many PCs). *'''C:''' β First [[hard disk drive]] partition. *'''D:''' to '''Z:''' β Other disk partitions get labeled here. Windows assigns the next free drive letter to the next drive it encounters while enumerating the disk drives on the system. Drives can be partitioned, thereby creating more drive letters. This applies to MS-DOS, as well as all Windows operating systems. Windows offers other ways to change the drive letters, either through the Disk Management snap-in or <code>[[diskpart]]</code>. MS-DOS typically uses parameters on the line loading device drivers inside the [[CONFIG.SYS]] file. Case-specific drive letters: *'''F:''' β First network drive if using [[Novell NetWare]]. *'''G:''' β "Google Drive File Stream" if using [[Google Drive]]. *'''H:''' β "Home" directory on a network server. *'''L:''' β Dynamically assigned [[load drive]] under Concurrent DOS, Multiuser DOS, System Manager and REAL/32.<ref name="DRI_1987_CDOS_User"/><ref name="DRI_1987_CDOS"/> *'''M:''' β Drive letter for optionally [[memory drive]] MDISK under Concurrent DOS.<!-- possibly also in Multiuser DOS, System Manager and REAL/32? --><ref name="DRI_1987_CDOS_User"/> *'''N:''', '''O:''', '''P:''' β Assignable [[floating drive]]s under CP/M-86 4.x, Personal CP/M-86 2.x, [[DOS Plus]] 1.1-2.1 (via BDOS call 0Fh), a concept later extended to any unused drive letters under Concurrent DOS, Multiuser DOS, System Manager, REAL/32 and DR DOS up to 6.0.<ref name="DRI_1987_CDOS_User"/><ref name="DRI_1987_CDOS"/> *'''Q:''' β Microsoft Office Click-to-Run virtualization. *'''U:''' β Unix-like ''unified filesystem'' with virtual directory <code>\DEV</code> for [[device file]]s under [[MiNT]], [[MagiC]], and [[MultiTOS]].<ref name="MagiC_2016_DriveU"/><ref name="FreeMiNT_2000"/> *'''Z:''' β First network drive if using [[Banyan VINES]], and the initial drive letter assignment for the virtual disk network in the [[DOSBox]] [[x86]] emulator. It is also the first letter selected by Windows for network resources, as it automatically selects from '''Z:''' downwards. By default, [[Wine (software)|Wine]] maps '''Z:''' to the root of the UNIX directory tree.<ref name="Wine"/> When there is no second physical floppy drive, drive '''B:''' can be used as a "virtual" floppy drive mapped onto the physical drive '''A:''', whereby the user would be prompted to switch floppies every time a read or write was required to whichever was the least recently used of '''A:''' or '''B:'''. This allows for much of the functionality of two floppy drives on a computer that has only one. This concept of multiple drive letters sharing a single physical device (optionally with different "views" of it) is not limited to the first floppy drive, but can be utilized for other drives as well by setting up additional block devices for them with the standard DOS [[DRIVER.SYS]] in [[CONFIG.SYS]]. Network drives are often assigned letters towards the end of the alphabet. This is often done to differentiate them from local drives: by using letters towards the end, it reduces the risk of an assignment conflict. It is especially true when the assignment is done automatically across a network (usually by a logon script). In most DOS systems, it is not possible to have more than 26 mounted drives. Atari GEMDOS supports 16 drive letters '''A:''' to '''P:''' only. The PalmDOS PCMCIA driver stack supports drive letters '''0:''', '''1:''', '''2:''', ... to address PCMCIA drive slots. Some Novell network drivers for DOS support up to 32 drive letters under compatible DOS versions. In addition, Novell DOS 7, OpenDOS 7.01, and DR-DOS 7.02 genuinely support a CONFIG.SYS <code>[[LASTDRIVE (CONFIG.SYS directive)|LASTDRIVE]]=32</code> directive in order to allocate up to 32 drive letters, named '''A:''' to '''Z:''', '''[:''', '''\:''', ''']:''', '''^:''', '''_:''' and '''`:'''. (DR-DOS 7.02-7.07 also supports <code>HILASTDRIVE</code> and <code>LASTDRIVEHIGH</code> directives in order to relocate drive structures into upper memory.) Some DOS application programs do not expect drive letters beyond '''Z:''' and will not work with them, therefore it is recommended to use them for special purposes or search drives. JP Software's [[4DOS]] command line processor supports drive letters beyond '''Z:''' in general, but since some of the letters clash with syntactical extensions of this command line processor, they need to be escaped in order to use them as drive letters. Windows 9x (MS-DOS 7.0/MS-DOS 7.1) added support for <code>LASTDRIVE=32</code> and <code>LASTDRIVEHIGH=32</code> as well. If access to more filesystems than '''Z:''' is required under Windows NT, [[Volume Mount Point]]s must be used.<ref name="Microsoft_Server"/> However, it is possible to mount non-letter drives, such as '''1:''', '''2:''', or '''!:''' using the command line <code>[[SUBST]]</code> utility in Windows XP or later (i.e. <code>SUBST 1: C:\TEMP</code>), but it is not officially supported and may break programs that assume that all drives are letters '''A:''' to '''Z:'''.
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