[NTFSDOS Logo]
Copyright © 1996-1997 Mark Russinovich and Bryce Cogswell
Last Updated February 3, 1997, Version 1.3R
Introduction NTFSDOS.EXE is a read-only network file system driver
for DOS/Windows that is able to recognize and mount
NTFS drives for transparent access. It makes NTFS
drives appear 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.
Enhancements Version 1.3 has the following enhancements over
over V1.21 V1.21:
* Drive letters can be individually assigned.
* Improved performance in large long filename
directories.
* Several minor bug fixes.
Contents of the The NTFSDOS package (see the bottom of this page)
Package contains the following files:
* README.TXT: This file
* README.TXT: This file
* NTFSHLP.VXD: Helper VxD needed only for long
filename support in Windows 95
Installation and To use NTFSDOS, simply execute it from the DOS
Use command line (DOS 5.0 or greater is required), or
from your AUTOEXEC.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 erver, it will resort to allocating 64KB of
conventional memory for ts cache. In either case, it
will inform you of its action.
NTFSDOS takes five command line parameters. The /L
parameter lets you specify which driver letters
NTFSDOS should attempt to use as it mounts NTFS
drives. The /C option lets you override the default
XMS cache size. The /V option directs NTFSDOS to
print some messages detailing the drives it looks at
the memory it allocates. The /X switch forces NTFSDOS
to use standard BIOS int 13 services. Use this if
NTFSDOS has problems with your computer's extended
int 13 services. Finally, the /N switch can be used
to disable NTFSDOS support for compression. Much of
the conventional memory that NTFSDOS normally uses is
for compression buffers, so if you will be accessing
drives or files that are not compressed and would
like to optimize NTFSDOS use of memory, use this
switch.
The syntax for these parameters is:
/L:<letter> Specifies drive letter to start
mounting at
/C:<size> Specifies size of XMS cache in KB
/V Verbose
/X Disable extended int 13 support
/N Disable support for compression
If You Have This section lists and addresses various issues that
Problems Running may arise when you run NTFSDOS.
NTFSDOS
* NTFSDOS does not recognize my NTFS drive
NTFSDOS does not handle cluster sizes > 4K on NT 4.0
formatted drives. This is rare, since NTFS
compression does not handle these cluster sizes
either.
NTFSDOS requires that disks be accessible via BIOS,
using the INT 13 or extended INT 13 services. In some
cases, SCSI drives may not be fully accessible
without a DOS device driver (see your SCSI adapter
documentation).
* NTFSDOS uses too much conventional memory
Some people have complained that NTFSDOS is a
memory hog. Unfortunately, this fact is largely
imposed on us by the architecture of NTFS itself
(sorry, but its a little more complicated than
FAT, and much more memory intensive), coupled
with our desire to provide reasonable
performance across a wide variety of NTFS
installations. In general, the footprint of
NTFSDOS increases largely with the clustersize
of the largest NTFS partition, and slightly with
the number of NTFS volumes mounted.
* 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, UNLESS the computer's
BIOS has extended INT 13 support for the drives
in question. The latter restrictions are due to
limitations in standard 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. 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 5, XCOPY
starts the Windows console program XCOPY32.EXE.
Reporting Bugs When you report a bug (see Reaching Us, below),
please provide the following information about your
system:
* disk types (IDE, etc.)
* disk and partition sizes
* BIOS version
* drive sizes and formats
* version of NT that was used to format NTFS
drives
* version of NTFSDOS you are using
* an output dump of NTFSDOS run with the /V
(verbose) option
* version of DOS and/or Windows you are running
NTFSDOS on
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.
NTFSDOS also uses the INT 2F/11 and INT 13 APIs.
Otherwise the magic is just memory and cache
management plus interpretation of the NTFS on-disk
structures.
Read-write A read-write version of NTFSDOS will eventually be
NTFSDOS ready. This is a long-term project and is not
presently near completion. Do not send us e-mail
inquiries about it.
If you have a dead system that you would like to
recover data from or repair, and you have access to a
second NT machine, you may want to try NTRecover,
another utility we have written. A read-only
NTRecover is available for free download, and with it
you can access the drives on the dead system from the
working system using native NT file systems and
uiltities. In fact, to NT the drives appear as if
they were local drives on the working system. With
the read/write version, you can copy/edit/delete
files.
Acknowlegements 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.
Andrew Schulman, et. al.'s, book, Undocumented DOS
2nd Edition (Addison-Wesley), was invaluable in
providing network redirector information necessary
for implementing NTFSDOS.
Download NTFSDOS (35KB)
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