Accessing Parallel Port


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Article ID: Q500001

The information in this article applies to:

  • Direct I/O, version 4.0, 4.1

For Direct I/O, version 4.2 and above see article Q500003.


Normally the parallel port (LPT) is controlled by Windows NT. Software needing direct access to the parallel ports registers does not run properly.
Direct I/O can be configured to grab the parallel port resources and allow those programs to run successfully.


Follow the steps given below to configure your system properly:

  1. Open the Direct I/O Control Panel
  2. Identify the parallel port you want to use and enter the resources in the tab I/O Ports
    LPT1:   378-37A
    LPT2:   278-27A
  3. Determine the type of application you want to run and enter the appropriate process name in the tab Security
    Win16:   NTVDM.EXE
    Win32:   Application name
  4. Check if your application utilizes the parallel port IRQ. If you are unsure skip this step. You can enter an IRQ later if your application failed to run because of a missing interrupt.
    LPT1:   7
    LPT2:   5
  5. Close the Direct I/O Control Panel and open the Devices Control Panel
  6. Select the Direct I/O device and press the Startup button
  7. Change the startup type to System and close the dialogs
  8. Reboot your system

Depending on your configuration you may notice some error messages at startup stating that the device parport.sys cannot be started. This occurs in cases when you have grabbed the only parallel port built into this PC. You can get rid of these messages by changing the startup mode of these devices to Disabled.


You cannot print to a parallel port grabbed by Direct I/O. Only one device has control over a given hardware resource, either parport.sys or Direct I/O.

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Last modified: 2018-04-24.
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