USBDLM is a Windows service that gives control over Windows' drive letter assignment for USB drives. Running as service makes it independent of the logged on user's privileges, so there is no need to give the users the privilege to change drive letters. It automatically solves conflicts between USB drives and network or subst drives of the currently logged on user. Furthermore you can define new default letters for USB drives and much more. It works on Windows XP to Windows 11 and Server 2003 to 2022.

Getting Started

When a removable drive (USB flash drive, flash card reader, portable hard drive) is attached for the first time, Windows mounts it to the first available "local" drive letter. If there is a network share on this letter, Windows XP will use it anyway for the new USB drive because since XP network shares are specific to the current user and not visible in the "System" context where the letter is assigned. The USB drive then appears to be invisible. This is fixed by XP-SP3 in most situations.
Windows can save only one letter per drive and one drive per letter. Therefore the assingments often overwrite each other, especially on low letters near the first available ones.
You can change the letter assignments in the Windows Disk Management Console with a lot of mouse clicks but you have to do it again for every new device.

  • USBDLM can for newly attached USB drives
  • check if the letter is used by a network share of the currently logged on user and assign the next letter that is really available
  • reserve letters, so they are not used for local drives
  • assign a letter from a list of new default letters, also dependent on many different criteria as the active user, drive type, connection (USB, FireWire), USB port, volume label, size and others
  • extract the letter from the volume label
  • assign letters for a specific USB drive by putting an INI file on the drive
  • remove the drive letters of card readers until a card is inserted
  • show a balloon tip with the assigned drive letter(s)
  • define autorun events depending on many different criteria
  • activate a basic protection against 'BadUSB' devices; USBDLM can ask on arrival of a USB keyboard or network device if it shall be activated
  • many other things, see help file, available online as HTML version too
  • All functions are applied to USB drives at the moment they are being attached, when the USBDLM service starts up and when a user logs on.
  • USBDLM runs as service under Windows XP, Vista, Windows 7/8/10/11 and all their Server Editions.

What's New

  • Bugfix: V5.5.10 did not register for volume notification, so almost nothing worked
  • Bugfix: USBDLM may crash when arrival and removal events are triggered in fast succession for the same drive
  • Bugfix: UsbDriveInfo showed a messagebox after writing a report by command-line
  • Bugfix: UsbDriveInfo showed "Error path not found" on Tools -> Compact VHD