Invalid drive specification
Microsoft MS-DOS
Severity: MinorWhat Does This Error Mean?
Invalid drive specification means you referenced a drive letter that DOS does not recognise. The drive may not exist, may not be configured in CONFIG.SYS, or you may have typed the wrong letter. Check which drives are available by trying A:, B:, C: and so on.
Affected Models
- MS-DOS 3.x
- MS-DOS 4.x
- MS-DOS 5.x
- MS-DOS 6.x
- PC-DOS
- FreeDOS
- DOSBox
Common Causes
- Typed a drive letter that is not assigned to any device
- CD-ROM drive not loaded (no MSCDEX driver in AUTOEXEC.BAT)
- Network drive not mapped or network drivers not loaded
- RAM disk driver not loaded in CONFIG.SYS
- In DOSBox: drive not mounted with the MOUNT command
How to Fix It
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Check which drive letters are available by typing each one.
Type C: and press Enter. If you get a prompt, that drive exists. Try D:, E:, and so on. Invalid drive specification on any letter means no device is assigned to it.
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For CD-ROM drives: make sure MSCDEX.EXE is loaded in AUTOEXEC.BAT.
CD-ROM drives in DOS require two components: a device driver in CONFIG.SYS and MSCDEX.EXE in AUTOEXEC.BAT. Without MSCDEX, the drive letter is not created even if the hardware works.
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In DOSBox: mount the drive before accessing it.
Type MOUNT D C:\CDGAMES -t cdrom to mount a folder as a CD-ROM drive D. Type MOUNT C C:\DOSGAMES to mount a folder as drive C. DOSBox does not automatically assign drive letters.
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Check CONFIG.SYS for LASTDRIVE= setting.
LASTDRIVE=E in CONFIG.SYS limits DOS to drives A through E. If you need drive letters beyond E (for networks or CD-ROMs), add LASTDRIVE=Z to CONFIG.SYS and reboot.
Frequently Asked Questions
How many drive letters does MS-DOS support?
DOS supports drive letters A through Z (26 total). A and B are reserved for floppy drives, C is typically the hard drive. The LASTDRIVE= setting in CONFIG.SYS controls how many letters DOS actually makes available.
Why does DOS use letters for drives instead of names?
Drive letters were inherited from CP/M, the operating system that preceded DOS. CP/M used A: and B: for its floppy drives, and when IBM adopted DOS for the PC, the convention continued. It remains in Windows to this day.