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NTFS File System Redirector for DOS/Windows V1.1 (read-only)

Last updated June 4, 1996

NTFSDOS.EXE is a network file system redirector for DOS/Windows that is able to recognize and mount NTFS drives for transparent access. It makes NTFS drives appear virtually indistinguishable from standard FAT drives, providing the ability to navigate, view and execute programs on them from DOS or from Windows, including from the Windows 3.1 File Manager and Windows 95 Explorer.

Please read this entire file before contacting us for help.

Click here to
download NTFSDOS.ZIP

Here is sample output from an NTFSDOS session under DOS 7.0 (Windows 95):

C:\ntfsdos>ntfsdos

NTFS File System Redirector for DOS/Windows V1.1 (read-only)
Copyright (C) 1996 Mark Russinovich and Bryce Cogswell

Initialized 500KB of XMS cache.

Mounting NTFS partition(0x80:3) as drive: H

C:\ntfsdos>h:

H:\>dir

 Volume in drive H is ntfs
 Directory of H:\

EMACS          <DIR>        03-16-96  8:31a emacs
FILEMON        <DIR>        04-18-96  3:30p filemon
               <DIR>        05-01-96  1:20p newlongfilename
NTICE          <DIR>        03-30-96  8:18a NTICE
PAGEFILE SYS    28,311,552  04-07-96 12:16p pagefile.sys
PROGRA~1       <DIR>        03-30-96  5:20a Program Files
RECYCLER       <DIR>        03-30-96  5:36a RECYCLER
TEMP           <DIR>        05-15-96 12:58a temp
USERS          <DIR>        03-16-96  3:27a users
WIN32APP       <DIR>        03-16-96  3:27a win32app
WINNT          <DIR>        03-30-96  8:41a WINNT
WINNT35        <DIR>        05-15-96 12:58a WINNT35
         1 file(s)     28,311,552 bytes
        11 dir(s)     388,284,416 bytes free

H:\>

Contents of the Package

README.TXT - this readme
NTFSDOS.EXE - DOS/Windows NTFS file-system driver
NTFSHLP.VXD - helper VxD needed only for long filename support in Windows 95

Security Implications

NTFSDOS raises some obvious questions about NT security. However, Microsoft's claims for NT security assume physical security. In a white paper "Windows NT File System: Built for Data Security", Microsoft denies that NTFSDOS has any implications for NT security: "Despite reports, this utility does not affect the ability of the Windows NT Server operating system to secure critical business data. The availability of this utility does, however, underscore one of the most important and fundamental necessities of network security the need for physically securing server hardware." Uh, okay, if you say so.

The PC Week (April 29, 1996) article mentioned in the Microsoft white paper was a small notice, "Utility threat to NT file system security", which said:

Two University of Oregon faculty members released an NT File System redirector for DOS and Windows that potentially provides an easy route to compromising NT security.
The utility, which is available at ftp://ftp.ora.com/pub/examples/windows/win95.update/schulman.html, makes NTFS files visible in the DOS/Windows File Allocation Table. The potential leak occurs when someone boots an Intel-based NT server from a DOS floppy, then uses the utility to read the NTFS.

Computerworld Australia (May 17, 1996) carried a lengthier article on NTFSDOS, "Cracks exposed in NT's security". A copy of this interesting article was posted by an OS/2 supporter to bit.listserv.os2-l:

[NTFSDOS's] ability to pick the locks on NT's file management system will shock large sites into a more realistic view of NT security, predicted Dr. Ian Graham, PC development manager at data security company, Eracom. Graham claimed many large sites, Including Australia's financial institutions, have put too much trust in NT workstation protection.
The appearance of NTFSDOS might correct that by graphically demonstrating they've enjoyed a false sense of security, he said....
Microsoft Australia marketing manager for NT workstations, Peter Moore, said that the reports underscore the need to apply basic corporate security precautions to PC networks.

Enhancements over V0.9

NTFSDOS V1.1 has been greatly improved over V0.9. Some of the changes include:

Drives are now accessible under Windows 3.1
Long filename support under DOS 7.0/Windows 95. NTFSDOS can now mount and access NTFS drives that have no short-file names.
Compressed files and directories. NTFSDOS understands the NTFS compression format so compressed files can be accessed transparently.
Instancing under Windows. Now you can open multiple DOS boxes under Windows, each with different NTFS drive current directories.
Redirector bugs fixed. NTFSDOS drives look to DOS and Windows exactly like local FAT drives. This means you can view and execute any files, such as bitmaps, Windows and DOS programs, that you would be able to on FAT drives, from Filemanager, Windows 95 explorer, or the DOS command prompt.
Greatly improved performance in directories with 100's of files.
Drive detection fixed. NTFSDOS no longer confuses HPFS drives for NTFS.
Uses XMS instead of EMS. This alleviates the need for EMM386 to be running for NTFSDOS to have a large cache.
Many minor bug fixes. NTFSDOS is now extremely robust.
Prevents itself from being run twice.

Installation and Use

To use NTFSDOS, simply execute it from the DOS command line (DOS 5.0 or greater is required), or from your UTOEXEC.BAT. Executing NTFSDOS before Windows is started will create NTFS drives that are visible globally once inside Windows. Executing NTFSDOS in a DOS box means that the NTFS drives only exist within the DOS box where NTFSDOS was executed.

When NTFSDOS starts, it will scan all hard-disk partitions on your system to look for NTFS drives. It will mount all NTFS drives it finds as unique DOS logical drive letters, and will inform you as it does so.

If you run NTFSDOS under DOS 7.0, NTFS drives will support long filename calls even before Windows starts. To propagate this support into Windows 95, NTFSDOS automatically has Windows run the NTFSHLP.VXD VxD device driver. No changes to SYSTEM.INI or the registry are necessary for this to occur - NTFSDOS will detect when Windows 95 starts and load the driver without user-intervention. You need NTFSHLP.VXD only if you will be running NTFSDOS with Windows 95.

NTFSDOS implements its own caching, and uses one of two types of memory, depending on how your system is configured. Its first choice is to use XMS memory for caching, as this minimizes demands placed on conventional memory. If you start NTFSDOS before Windows, then HIMEM.SYS, which can be found in the WINDOWS directory under Windows 95 or the DOS directory under Windows 3.1, or its equivalent, must be started before NTFSDOS. If NTFSDOS does not detect an XMS server, it will resort to allocating 64KB of conventional memory for its cache. In either case, it will inform you of its action.

There is no way to unload NTFSDOS from memory once it has started.

If You Have Problems Running NTFSDOS

Accessing an NTFSDOS drive causes a hang or crash

NTFSDOS does not support disk striping. Further, it cannot handle drives that are on partitions extending beyond the 2GB boundary, or that are larger than 2GB in size. The latter restrictions are due to limitations in disk BIOS code that prevent it from addressing sectors 2GB or more from the start of a disk.

NTFSDOS has not been thoroughly bullet-proofed against corrupt NTFS drive data structures, so it may cause Windows to crash or hang when it runs into problems. To insure that a crash or hang is due to a problem with NTFSDOS rather than your NTFS drive, be sure to chkdsk the drive from Windows NT and try NTFSDOS again.

Starting programs or loading files seems very slow

Access of large compressed files may be noticeably slower than of their non-compressed versions.

File times are not correct when running under DOS 7.0 without Windows 95

This problem is due to the fact that NTFS and LFN FAT time stamps are stored in Coordinated Universal Time (UTC), which is based on Greenwich Mean Time, and Windows 95 automatically converts times stamps returned by LFN calls to local time. Since local time zone information is not accessible outside of Windows 95, running NTFSDOS under DOS 7.0 without Windows 95 results in the display of unadjusted times.

Programs complain about not being able to find files when they are there

A directory listing of files that have no short filename will result in the short filename field of the listing being blank (see the file, "newlongfilename," in the sample listing above). Changing the current directory to a path where any component of the pathname does not have a short filename will result in all short filename calls failing while in the directory. This makes most Windows 3.1 and DOS programs and many DOS commands (e.g. MORE) inoperative in these directories. However, LFN calls are supported in these directories.

Data read from a file appears to be corrupt

Since this work is based on reverse-engineering rather than official Microsoft specifications (which are reportedly available under special circumstances for large amounts of money), we do not guarantee data integrity of NTFSDOS drives. This is especially important if you are considering using NTFSDOS as a file backup utility.

Files or directories seem to be missing

Remember that files and directories that were created with no DOS 8.3 short filenames will not be visible if you are running DOS versions earlier than 7.0.

You get the message "No drive letter to mount NTFS partition..."

If NTFSDOS complains that it cannot mount a drive because there are no available drive letters, you must find the line in your CONFIG.SYS that begins with "LASTDRIVE=". If you do not find one, then add one. Set the LASTDRIVE variable to a letter that is greater, by the number of NTFS drives on your system, than the largest drive letter you normally have under DOS/Windows. For example, if the highest drive letter normally in use is E: and you have two NTFS drives, set LASTDRIVE to G: with a statement in CONFIG.SYS like:

LASTDRIVE=G:

If you still get the message then increment the letter and try again. Remember to reboot after every change to CONFIG.SYS.

You get the message "Could not allocate XMS or conventional cache"

Memory usage on your machine is so high that NTFSDOS could not allocate 64KB for a conventional cache. Try removing unnecessary TSRs and drivers and/or running a DOS memory optimizer or manager.

XCOPY does not work in a DOS box

XCOPY will not work on NTFS drives that are mounted in DOS boxes under Windows 95 (e.g. running NTFSDOS in a DOS box). This is because you cannot run Windows programs off of non-global drives, and under Windows 95, XCOPY starts the Windows console program XCOPY32.EXE.

Implementation

NTFSDOS scans the system's partition tables looking for partitions that have the NTFS attribute byte. When it finds one, it looks for an unused DOS driver letter and registers a network drive on it. After it completes the drive search it hooks the network redirector interrupt and goes resident. Requests come into NTFSDOS as full path names, or continuations of a previous directory traversal (as with findnext), so it proceeds to determine where, based on NTFS internal data structures, the target file is located. When it retrieves the header for the target file it can determine where the file's data is located, and read it when it receives requests to do so.

To provide long filename support (LFN), NTFSDOS hooks INT 21/AH=0x71 calls and implements LFN functionality when it sees an LFN call. Under Windows 95, NTFSHLP.VXD is required to send LFN calls down to the NTFSDOS for it to process; otherwise NTFSDOS would not see LFN calls since Windows assumes DOS redirected drives do not provide LFN support.

The only API NTFSDOS uses is the INT 2F/11 API and INT 13. Otherwise the magic is just memory and cache management plus interpretation of the NTFS disk structures.

Write-Access NTFSDOS

If there is sufficient interest we will implement a write-access version of NTFSDOS. The expected cost of the version will be $35. If you would like to purchase a copy if and when it becomes available, please notify us (see Reaching Us, below) by e-mail and be sure to let us know how many copies you would want.

Reaching Us

We would appreciate any feedback you have concerning this utility including suggestions and bug reports. Mark can be reached at markr@numega.com, and Bryce can be reached at cogswell@cs.uoregon.edu.

NOTE: this product is in no way connected with, or endorsed by, Nu-Mega Technologies or the University of Oregon.

Acknowledgments

We thank everybody that e-mailed us with bug reports and other feedback.

Significant understanding of the NTFS file system layout was derived by studying the Linux-based NTFS driver code maintained by Martin von Loewis. We acknowledge his indirect contribution to this endeavor.

The book Undocumented DOS by Andrew Schulman et al. (2nd edition, Addison-Wesley), was invaluable in providing network redirector information necessary for implementing NTFSDOS.

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