USBDLM V5.2.1 - USB Drive Letter Manager for Windows

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  What it is
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.

  What it is not
USBDLM isn't a wonder tool. If Windows has problems with the USB drives itself then USBDLM cannot fix it.
Here are some tips for solving problems with USB drives.

  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 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 and all their Server Editions.


Unzip the distribution (USBDLM.ZIP) file to "C:\Program Files" (an USBDLM folder is included).

Then execute the _edit-ini.cmd which creates or opens the configuration file, the USBDLM.INI.

Then register USBDLM as Windows service and start it by executing the


You can change the USBDLM.INI without restarting the service because it's checked for changes each time a new drive is attached.

You can deregister the USBDLM service by executing the

Both can be done without the message box by using the following USBDLM commandline parameters
USBDLM -silentregister
USBDLM -silentderegister

It returns Errorlevel 0 on success, 1 on failure.

You can stop and start the installed service by means of the _service_stop.cmd and _service_start.cmd and of course by "net stop USBDLM" / "net start USBDLM".


Running without a configuration USBDLM only prevents that a new drive gets the letter of a network share or a subst drive of the currently logged on user. It remounts then to the next letter that is really available.

USBDLM is configured thru a text file, the USBDLM.INI. The USBDLM.INI is read from the folder of the USBDLM.EXE.
If required, read at Wikipedia how INI files work.

New default letters for new USB drives (flash or harddrive)

Have a look into the help file USBDLM_ENG.CHM for more details. If you get the "cannot display the webpage" error then the help file has the NTFS file attribute "downloaded from untrusted source" and Microsoft doesn't trust its own CHM file format. To fix this, right click the USBDLM_E.CHM, select Properties and click "Unblock".
The help file is available online as HTML version too.

Card Readers

The typical 20-in-1 card reader eats one drive letter for each of its slots - if we own a card for or not. USBDLM can remove the reader's drive letters until a media is inserted.

USBDLM assigns then a drive letter as configured. If you need different drive letters for a multislot cardreader, then use the criterion "DeviceType" in a DriveLetters section (MSCR is short for MultiSlotCardReader):

Network drive letters

You can prevent Windows mounting local drives to certain letters by putting them into section NetworkLetters. This is especially useful for letters of network shares which Windows may assign to USB drives while booting. Do not configure other letters than network, subst and TrueCrypt drives here!


Balloon Tips

USBDLM can show a balloon tip with information about the drive letter(s) or mount points used for a just attached drive:


There is much more USBDLM can do, just take some time and read the help file...

USBDLM V5 gets Balloontips on removal, here I need translations from the text snippets in French, Italian, Spanish and Portuguese as USBDLM V4 already has:

  • Safely removed
  • Unsafely removed
  • Removed
  • Ejected
  • Network Drive
  • Subst Drive

  Latest History
For the complete history check out the help file which is available online as HTML version too.

V5.2.1 (10 May 2016)

  • New: Unwanted EventLog items can be deactivated
V5.2.0 (8 May 2016)
  • Bugfix: USBDLM_usr.exe (still) sometimes caused permanent CPU load
  • Bugfix: Since V5.0 USBDLM has set WriteCacheEnableOverride=1 into the Registry for newly attached USB drives if there was no UsbWriteCacheEnable configured
  • New: EventLog can be written to the LogFile instead
V5.1.8 (25 April 2016)
  • Bugfix: USBDLM_usr.exe sometimes caused permanent CPU load, probably since V5.0
  • Bugfix: open= did not work with document files since V5.1.3
  • Bugfix: USB speed icon not shown on some USB controllers running with other than Microsoft drivers
  • Bugfix: Maximum connection speed of USB 2.0 High-Speed devices running at Full-Speed shown wrong as USB 1.1 Full-Speed
V5.1.7 (07 April 2016)
  • Bugfix: Since V5.1.5 the PortName criteria did not work again for USB drives
  • Bugfix: Several minor issues fixed
  • New: OnArrival is triggered on instertion of a media into a CD/DVD drive
V5.1.6 (17 March 2016)
  • Bugfix: Since V5.0 USBDLM stoopped assigning drive letters after attaching a drive with a BusType for which there is no section DriveLetters
V5.1.5 (11 March 2016)
  • Bugfix: In V5.1.4 crash on balloon tip with NTFS mountpoint
  • Bugfix: Since V5.0 settings in the registry did not work
V5.1.4 (09 March 2016)
  • Bugfix: In V5.1.3 the Win32 USBDLM.exe was compiled without optimization for "Minimize Size", besides the 100KB bigger USBDLM.exe this made some virus scanners believing to detect a virus
  • Bugfix: Since V5.0 the PortName criteria did not work for USB drives
  • Rollback: Default for SuppressWindowsBalloons is 1 again; 2 (deactivating Windows balloon tips temporarily) makes the Windows tray icon for "Safely remove Hardware" stop working
V5.1.3 (07 March 2016)
  • Bugfix: Occational crashes fixed
V5.1.2 (03. March 2016)
  • Bugfix: Logdatei angelegt trotz WriteLogFile=0
V5.1.1 (29. Februar 2016)
  • Bugfix: AutoDismount-TrayIcon was shown even there is no [AutoDismount] section
V5.1.0 (29. Februar 2016)
  • Bugfix: In Abschnitten wie [OnArrival] wurden die Zeilen system, elevated und restricted immer als gleich 1 bewertet, falls vorhanden
  • Bugfix: In Abschnitten wie [OnArrival] mit nur einer open= Zeile wurden nur Optionen berwertet die nach der open-Zeile stehen
  • Neu: Tray-Icon mit Anzeige des Auto-Dismount-Status
  • Neu: DismountOnSleep weckt keine schlafenden Laufwerke mehr auf
V5.0.2 (19 Jan 2016)
  • Bugfix: In a USBDLM.INI on an attached drive only Letter= and Letters= worked, but Letter1= etc possibly not
V5.0.1 (18 Jan 2016)
  • Bugfix: _edit-ini.cmd failed to create a USBDLM.INI when it had no write privileges; now Admin previleges are requested
  • Bugfix: USB speed in the balloon tip was wrong when the USB port number could not be determined, for instance if in the location information there isn't something like Port_#0002.Hub_#0003 or the address value is zero. Now the port number is determined by means of the USB-API.
  • Bugfix: The section [NetworkLetters] did not work in V5.0.0 if there was not section [DriveLetters]
V5.0.0 (17 Jan 2016)
  • New: _install.cmd and _uninstall.cmd renamed to what they really do: _service_register.cmd and _service_deregister.cmd; _start.cmd and stop.cmd renamed to _service_start.cmd and _service_stop.cmd to fit in the new naming scheme
  • New: For sections and values there is no more need for numbering; For unnumbered sections the order of appearence is what counts
  • New: Ballontips show in the icon if a USB drive is running at Full-, High-Speed, SuperSpeed or SuperSpeedPlus
  • New: Ballontips on removal with information if the removal was safe or not (still need translations for new texts)
  • New: Compact balloon tips for multi-slot card readers if only one slot has a media present
  • New: Balloontips can be customized way more flexible
  • New: AutoDismount
  • New: Suppressing Windows Balloontips works under Windows 10
  • Bugfix: After a successful request for a password sometimes no drive letter was assigned
  • Bugfix: Removal Policy was written to the registry even no OptimizeUsbDrivesForSpeed parameter was configured



For home users I suggest the ZIP file. Just unzip to "C:\Program Files" and run the _service_register.cmd - this registers USBDLM as Windows service and starts it.
The _edit_ini.cmd opens the configuration files USBDLM.INI with admin previleges in the Windows text editor, if there no USBDLM.INI it creates one first, containing some basic settings.
The MSI is for admins who want to deploy the software in their network. An MSI with integrated USBDLM.INI is not difficult to create, see USBDLM help under Creating an MSI. There is also some information about using the MSI for USBDLM updates.

The software is fully functional and does not expire. There is no 'full version'.

Download latest release:
(about 856 KB)
(about 900 KB)

(about 923 KB)
(about 966 KB)

The last USBDLM V4, just in case of serious problems with V5.x: usbdlm491.msi usbdlm491_x64.msi

ListUsbDrives - the commandline version of UsbDriveInfo:

Previous releases


  Conditions and Prices USBDLM

USBDLM is Freeware for private and educational (schools, colleges, universities) use only. The students shall outnumber all others.
Otherwise one licence per computer is required after a 30 day test period even though the software does not expire.

To support admins in schools which are often voluntary workers I made USBDLM freeware for schools, colleges and universities. But that's the line I've drawn and even your organization is non profit, good and important I have to say, it's beyond that line. Ask me for a discount in this case.

I don't ask for donations but some users insist, so
PayPal and BitCoins 19ktLtQr3URoi1YM6ZBy9SRodteGiNf9Wd / QR are welcome.

Prices with effect from June 2011
(Euro prices are constant, USD prices are floating):

Purchase of: 
Price per licence
1 to 9 licences
15.00 USD
10 to 99 licences
9.00 USD
100 to 999 licences
6.75 USD
1000 to 9999 licences
4.50 USD
>10000 licences
2.25 USD

You can order directly at me, I send offer and invoice on request.
An online order is possible at the KAGI online Shop (USA, California) with credit card, check or cash. VAT is charged depending on your country and can be skipped by having a VAT ID number.

The licence is delivered as licence number by eMail or on the invoice. It's not required for the software, the software is not limited in any way and it does not expire.

KAGI Online Shop (USA, California)

All licences are not limited in time and valid for future versions too. All updates are free of charge. Purchasers of V1.x, etc are free to use up to V5.x.


Counter since Feb. 1998

last change: 10 May 2016

The phone number is here because of the strange german law. Please don't call me, write an eMail instead.