Printing to Windows LPT1.OS2 or LPT1.DOS Port

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You may be unable to print from Microsoft Windows version 3.0 or 3.1 to the LPT1: port, although you can print to the LPT1.OS2 port, or LPT1.DOS port if using Windows 3.1. Some networks and print-sharing devices may require using the LPT1.OS2 or LPT1.DOS port. For the most part, this should be considered a temporary workaround. If you can print to LPT1.OS2 or LPT1.DOS and cannot print to LPT1, the reason is probably one of the following:
  1. Windows cannot create temporary files. This could be caused by any of the following:

    1. SET TEMP points to a nonexistent directory.
    2. SET TEMP points to a directory where you don't have create, modify, or write privileges.
    3. The SET TEMP line is not typed properly.
    4. SET TEMP points to a directory with little or no disk space.
    5. The SET TEMP line does not exist and Windows is trying to create temporary files in a directory that falls into category b or d above.
    6. FAT (file allocation table) is corrupt. Using the CHKDSK/F command might correct this.
  2. Poor cabling or printer-to-computer wiring exists. Try a different cable or verify that the cable is firmly connected to the printer and computer.


When Windows prints to a port, such as LPT1:, it uses a printing method that allows it to detect errors on the printer. While this method has advantages, it is not supported by some network software packages. When Windows prints to LPT1.OS2 or LPT1.DOS, a different method of printing is used that does not allow Windows to check for errors during printing. As a result, garbled output may occur during printing, especially when printing large files.

When Windows prints to the LPT1.OS2 or LPT1.DOS port, it prints to a file named LPT1.OS2 or LPT1.DOS. When DOS gets the request from Windows to open the file LPT1.OS2 or LPT1.DOS, it interprets that as a request to send data to the printer port, and it sends the data out through its own printing handler. Because Windows thinks that LPT1.OS2 or LPT1.DOS is a DOS file, the Print Manager is not used. Windows will not spool output to this port.

The extension .OS2 or .DOS is a dummy; any extension could be used with the same effect. Ports other than LPT1: can be printed to this way. Printing to the file LPT2.XYZ causes data to be sent to a printer on the computer's LPT2: port. Although you can print to COM ports in this manner (for example, COM1.PRN), it is not recommended because it requires a MODE statement in MS-DOS with the proper communication parameters.

Note: This technique is a WORKAROUND to a printer problem. It does not truly solve the problem, although it does indicate that the problem is probably NOT in the Windows printer driver. When possible, other Windows troubleshooting steps should be tried to avoid future difficulties, even if using LPT1.OS2 or LPT1.DOS seems to solve the problem. For more information on troubleshooting Windows printing problems, query on the following words:
tshoot and printing


Article ID: 68652 - Last Review: February 27, 2014 - Revision: 3.0
  • Microsoft Windows 3.0 Standard Edition
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