DOCUMENT:Q167969  09-AUG-2001  [winnt]
TITLE   :Under Windows NT, Win16 Applications Opening MS-DOS Devices Fail
PRODUCT :Microsoft Windows NT
PROD/VER:winnt:4.0
OPER/SYS:
KEYWORDS:kb3rdparty kbWinNT400sp4fix

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The information in this article applies to:

 - Microsoft Windows NT Workstation version 4.0 
 - Microsoft Windows NT Server version 4.0 
 - Microsoft Windows NT Server version 4.0, Terminal Server Edition 
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SYMPTOMS
========

Under certain circumstances, data written to LPT1 from a 16-bit Windows
application running under Windows NT can corrupt other files. This corruption
occurs when the application opens any MS-DOS device (as listed by MEM /D; for
example, LPT1, COM1, CON, and so on) through the _lopen() RTL function and opens
other data files. When the application writes data out through the LPT1 handle,
the data is misrouted to one of the other files.

CAUSE
=====

Some devices are handled internally by NTDOS without calling on the Win32 I/O
system directly. For example, LPT1 is handled by calling the Windows NT emulated
BIOS, which in turn uses OUT instructions to feed the data to the emulated LPT1
port. In this case, WOW mishandles several Interrupt 21 calls, including read
file and write file, trying to pass these calls to Win32 but using an
uninitialized bit of memory instead of a valid Win32 file handle. In some cases,
this uninitialized memory will contain a value that is a valid handle value in
the WOW process, and the data will be read from or written to that file instead
of the intended device. In other cases, the Win32 file API fails because the
handle is invalid.

RESOLUTION
==========

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or
Windows NT Server 4.0, Terminal Server Edition. For additional information,
please see the following article in the Microsoft Knowledge Base:

   Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack


STATUS
======

Microsoft has confirmed this to be a problem in Windows NT 4.0 and Windows NT
Server 4.0, Terminal Server Edition. This problem was first corrected in Windows
NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition
Service Pack 4.



MORE INFORMATION
================

It is highly irregular for a 16-bit Windows application to write to LPT1 through
MS-DOS; the entire Windows 3.1/Windows 95 GUI will stop responding if the
printer is slow or out of paper. The correct way would be to use OpenComm() and
WriteComm(), which perform the write in the background (using an interrupt
service routine) instead of blocking the computer (or WOW in this case) until
the write completes.

Additional query words:

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Keywords          : kb3rdparty kbWinNT400sp4fix 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbNTTermServ400 kbNTTermServSearch
Version           : winnt:4.0
Hardware          : x86
Issue type        : kbbug
Solution Type     : kbfix

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