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Control USB drive letter assignment in Windows with USBDLM

When a removable drive like a pen drive or external hard disk is attached to the computer, Windows assigns it to the first available 'local' drive letter. If the computer is a part of a network and even if there is a network share on this letter, Windows XP will use it anyway for the new USB drive. This results in conflict between the shared hard drive and the removable drive and as a result, often the USB drive appears to be invisible. The drive letter can be changed through the Administrative Tools in the control panel, but it has to be done every time a USB drive is plugged into the system.

To solve this issue and efficiently manage drive letter assignment of removable drives, there is a tool called USBDLM. USBDLM runs as a service and allows you to reserve letters, not used by any shared drives, to be used whenever any removable drive is attached to the computer. Any USB drive will then always take a particular drive letter(s) that the user assigns and not the next available letter.

USBDLM can perform a number of functions 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
  • 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

To install USBDLM, download USBDLM V4.2.2 (about 282KB) and unzip it to C:\USBDLM. Now double-click on _install.cmd to install the service. Immediately after, a file USBDLM.ini will be created. Open the file in Notepad and add these lines:


Here, U,Y,Z are the letters that are reserved for removable drives. You can use any other letters. USBDLM can have up to 9 'LetterX' entries in each section and they don't have to be continuous.

The INI file can be further configured to enable more features, but the current one will work for most users. The other features include excluding drive letters, managing letter assignment for card readers, enabling balloon tips etc which are explained in the accompanying help file. Read it if you wish to use those features.


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