Drive naming scheme DOS

in dos, drives referred identifying letters. standard practice reserve , b floppy drives. on systems 1 floppy drive dos assigns both letters drive, prompting user swap disks programs alternate access between them. facilitates copying floppy floppy or having program run 1 floppy while accessing data on another. hard drives assigned letters c , d . dos support 1 active partition per drive. support more hard drives became available, developed first assigning drive letter each drive s active primary partition, making second pass on drives allocate letters logical drives in extended partition, third pass give other non-active primary partitions names (where such additional partitions existed , contained dos-supported file system). lastly, dos allocates letters optical disc drives, ram disks, , other hardware. letter assignments occur in order drivers loaded, drivers can instruct dos assign different letter; drivers network drives, example, typically assign letters nearer end of alphabet.

because dos applications use these drive letters directly (unlike /dev directory in unix-like systems), can disrupted adding new hardware needs drive letter. example addition of new hard drive having primary partition pre-existing hard drive contains logical drives in extended partitions; new drive assigned letter assigned 1 of extended partition logical drives. moreover, adding new hard drive having logical drives in extended partition still disrupt letters of ram disks , optical drives. problem persisted through microsoft s dos-based 9x versions of windows until replaced versions based on nt line, preserves letters of existing drives until user changes them.

under dos, problem can worked around defining subst drive , installing dos program logical drive. assignment of drive changed in batch job whenever application starts. under versions of concurrent dos, under multiuser dos, system manager , real/32, reserved drive letter l: automatically assigned corresponding load drive whenever application starts.