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HomeTroubleshooting  •  LT Win Modem  •  Windows NT, ME, 2k & Linux  ̣
About the LT 33.6k/AT&T Trouble with the LT NT, 2k, ME & Linux Compaq & LT
What Driver Where to find driver Upgrade Procedure AT Commands Handshake/Diags

LT & Windows Versions:  Me, NT, 2000, XP
LT & Linux


While the LT is supported in WindowsNT in Intel-based machines, IBM, HP, and others supply the modem without any support for NT. The driver for NT (ltmodem.sys) can easily be found below - it is included in all Lucent driver releases. However, getting the modem installed properly in a Windows NT system can be challenging. If you have an uninstalled modem, I recommend starting with the latest generic driver.

Albert Ho developed these instructions to get the Dell Inspiron 7000's LT to work with NT. (They may also give those with non-Dell NT systems some ideas on how to deal with installation difficulties, and has been updated with other user-supplied NT experiences.) I have my IBM-supplied ISA-LT modem installed on my Aptiva in both Windows95 and WindowsNT Workstation/SP3.

Releases >5.53 of the driver fix a bug that affects some NT4 users getting blue screen. If you have a Compaq system and want to use NT4 & the Compaq modem - you need some special files - available from Modemsite. Release 5.66 fixes some NT-specific (BSOD) problems, and also includes a new, simpler installation program that may make installation and upgrading the modem easier. See the Where to Find Driver page.

Installation - An NT-specific setup program is available for driver version 5.54. The file contains a setup program only for NT4 to replace the setup.exe file in the modem554.exe archive. Note that in many instances, modem554.exe will install without any problem; you should try the modified setup only if you are having trouble installing the modem with NT4. Version 5.66 may provide better NT support and easier installation and upgrades.

I have added a page describing my March '01 experience removing the LT-based Zoom 3025L from WindowsNT, and re-installation trouble.


Windows2000 (NT5) cannot use any of the released driver and installation files below version 5.66. Support for the LT modem is included with the Microsoft Win2k CD.  A zip file containing 3 NT5 ltmdMnt.sys files from beta 3, RC1 & RC2 is available for download: click here. With release 5.66 of the generic driver, Windows2000 support is included, and modem566.exe (or later versions) should install/upgrade the modem in Windows95/98/NT & 2000 - the key word here is should. Some users can upgrade Win2K LT support to 5.66, others cannot. It depends upon the type of LT and the Win2K build. 

The driver included with the retail version is 5.41G6. The latest Lucent generic release available on this site is reported to install correctly in Windows2000 - at least some of the time. There is an issue with the Dell 7000 notebook - see MS KB Q247152. There is also an issue with signed/unsigned drivers and Win2k's file protection feature that will automatically restore the original old driver undoing your update of the driver! [This issue may be corrected with driver 5.79 or higher - not released as of 23-Jun-00.]* A 5.79 Win2k-only driver is available from Fujitsu's site in Japanese - see the Driver page.

'Kennethxu' has created a modified .inf file/driver package for Win2k that allows easy switching among driver versions in Windows2k: See Kenneth's page.

I have successfully upgraded LT Modem only with process described on this page.

When upgrading to Windows2000, users with installed LT modems will receive a Microsoft message indicating the old driver will not work, and will be disabled during the upgrade. The message further states "If your modem is supported by Windows 2000, a new driver will be installed during Windows 2000 Setup." Microsoft has a web-based Hardware Compatibility List (HCL) that can be used to determine whether a modem is [supposed to be] compatible with Windows2000, NT4, 95 and/or 98. It appears that the design of Windows2K will prevent update/change of the driver by methods that work with Win 95/98/NT. You cannot replace the ltmdnt.sys file with another version successfully - Win2K will restore the old version from its driver cache. 

It is possible to disable driver protection by modifying the registry. Remember, modifying registry can create a non-functional system!

If not already present, add a Dword value at
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon called SFCDisable and set value to 0xffffff9d  This disables the System File Checker (set to "0" to enable again).

* - Following is excerpt from MS Technet:

In Windows 2000, a new feature called System File Protection (SFP), will prevent the replacement of certain monitored system files. By preventing the replacement of essential system files, file version mismatches can be avoided.

SFP provides protection for system files by using a background mechanism that runs inside Winlogon.exe on a Windows 2000–based system. At the end of GUI-mode setup, SFP runs a scan of all protected files to ensure that they have not been modified by applications installed using unattended installation. After successful startup, the System File Protection service will perform a check of all catalog (.cat) files used to track correct file versions. If any catalog files are missing or corrupted, SFP will rename the affected catalog file and retrieve a cached version of that file from the dllcache directory. If a cached copy of the catalog file is not available in dllcache, SFP request the appropriate media (that is, Windows 2000 Service Pack, Windows 2000 Hotfix, and so on) to retrieve a pristine copy of the catalog file.

System File Protection is triggered when it receives a directory change notification on a file in a protected directory. Once it receives this notification, SFP will determine which file was changed. If the file is protected, SFP will look up the file signature in a catalog file to determine if the new file is the correct Microsoft version. If it is not, then the system either replaces the file from the dllcache directory or distribution media, depending on whether or not the file is located in dllcache. 

Code Signing

Code Signing technology, included in Windows 2000, complements System File Protection by using existing Digital Signature cryptographic technology to verify the source of a system file before it is installed.

A hash (encryption) of the driver binary and relevant information are stored in a catalog (.cat) file, and the .cat file is signed with the Microsoft digital signature. The binary itself is not touched; only a .cat file is created for each driver package and the .cat file is signed with a Microsoft digital signature. The relationship between the driver package and its .cat file is referenced in the driver's .inf file and maintained by the system after the driver is installed.

System File Protection uses the file signatures and catalog files generated by Code Signing to verify if protected system files are the correct Microsoft versions. System File Protection does not generate signatures of any type. So, while Code Signing is the means of tracking a file's version and creator, System File Protection is the enforcement mechanism that uses Code Signing signatures and catalog files to keep system files at their correct versions.

Driver Signing

To assure users that device drivers loading on their systems are certified production grade products, or notify them if such is not the case, Microsoft provides cryptographic signing on the binary driver code.

To promote and advance the quality of drivers, to provide a better user experience, and to reduce support costs for vendors and total cost of ownership (TCO) for customers, Microsoft has begun digitally signing drivers that pass the Windows Hardware Quality Labs (WHQL) tests. Such certification proves to users that the drivers they employ are identical to those Microsoft has tested, and flags any changes after a product is put on the Hardware Compatibility List.

Driver Signing operates as a driver is installed, rather than as a system boots. The three primary categories of driver verification can be simply described as Fail, Warn, and Ignore. Fail prevents unsigned code from being loaded. Warn provides a prominent message to tell the user that unsigned code is being loaded. Ignore loads drivers without notification, if the user or administrator so chooses. Driver Signing is configurable through a control panel to allow different types of drivers to be treated differently; for example, video drivers can operate in Warn mode, while network drivers operate in Fail mode.

It is important to note that digital signatures are associated with individual driver packages and are recognized by Windows 98, Windows 2000, and future operating systems. The operating system performs signature detection during any Plug and Play operation when the user runs the Control Panel Add New Hardware application.

Drivers will be digitally signed as part of WHQL testing if they run on Windows 98 and Windows 2000. (Only signed drivers are published on the Windows Update web site at .)

Windows ME

Windows ME  ships with a 5.79 ME-compatible driver. Note that the ME operating system is basically Win98-3rd edition. While WinME is able to use old .vxd drivers, it will default to new WDM-compliant (.sys) drivers. It is possible - but tricky - to switch from WDM/.sys drivers to older .vxd versions. There is discussion of this on the LT board of Forum56.

Some users report problems using the 5.79 (and later) WDM drivers: the modem installs, but connections go 'dead'. If you are upgrading Windows 95 or 98 system to WinMe: if you remove the modem from Control Panel->System Device Manager but leave the driver (ltmodem.vxd) in the \windows\system directory, WinMe should install your modem with existing .vxd drivers. 

When you do a new installation of Me - as opposed to an upgrade - the WDM driver will automatically be installed if your modem is physically installed in the system. Leave it out! Then, you follow procedure below without needing ltremove. Windows Me installs drivers automatically for devices it detects - and this detection is based upon the PCI ID of the device, and it's definition in an .inf file. If Windows recognizes the device, you do not have an opportunity to pick a different driver or prevent the default driver from being installed. The solution is to remove the definition of the device:

If you have installed the LT modem with WDM drivers in WinMe and wish to switch to .vxd drivers:
Extract the files in modem575.exe (or earlier) to a folder. Run ltremove.exe from 5.79 or later (see bottom of this page.) Go to [Control Panel] System -> Properties and remove the WDM modem enumerator. Remove or rename the wdmmdmis.inf and wdmmdmcb.inf files from the \windows\inf directory**. Reboot the computer. When Windows detects the modem, use the Have Disk option to install support from the folder in the first step. To upgrade to 5.79 or later, use the .vxd copy method (see this page).

**- You should make a copy of these files in another backup location first. This procedure removes the Microsoft file that makes Me automatically identify and install WDM support for Lucent-based Win Modems. If Windows still detects and automatically installs WDM modem driver, you may have a third-party .inf file that identifies your modem. Use a tool like PCITree to determine the PCI ID of your modem, then search the \windows\inf directory for .inf files that contain your modem's PCI ID and rename or copy and remove these files.

Also see: Microsoft Articles on Windows Modems:
   Windows Modem Update 
   Modems In Windows Operating Systems 
   What does WDM Mean to Device Driver Writers? 
   Adding a VxD Interface to Sys Drivers 

Windows XP

Windows XP comes with a generic driver for LT modems. The version depends upon the XP service release. In most cases, anytime an LT modem is placed in an XP machine, it will be detected, and the XP-supplied driver will automatically install when the system is booted. 

Windows XP comes with driver protection similar to Windows 2000 (see above). Updating to the latest (or recent) generic driver is accomplished by running the driver's setup.exe and continuing when warned that the driver hasn't passed "Windows Logo Testing". Also see: Windows XP & Modems.

Linux Support

Supported since Sep '01 - The LT modem can be used in many Linux systems with the appropriate driver. Linux "support" first appeared in 2001 with a binary driver release (no source code) based upon generic version 5.68.

Cristoph Hebeisen maintains a page with Linux driver packages for LT Win Modems. Latest driver is based on generic driver version 8.26. There is an archive of older versions as well. (The 8.26a9 and 6.00c packages are also at Modemsite downloads.)

For more information on the LT & Linux (as well as other software modems and Linux), see /sean/linux/stodolsk and, and join the DISCUSSION list [to get e-mail] and/or use the archives to stay abreast of the latest developments.

A page by Allin Cottrel on getting the IBM Thinkpad 390E to work with Linux, including the bundled LT modem, is at the Wake Forest University site.

* - The site has version 5.68 which works only with specific kernel versions; Info on 5.78 can be found in the discussion archive where you will find things like:

Have you looked at the half open/half closed lucent driver?  You might be
able to hack something into working there... 
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