HOWTO: Remove Serial Port Sharing feature


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Article ID: Q700008

The information in this article applies to:

  • Direct I/O, version 4.3, 4.4


One requirement for the Serial Port Sharing feature of Direct I/O is an ACPI-enabled system.

This article discusses a way to utilize Direct I/O on non-ACPI-enabled systems.


Beginning with Windows 2000 Microsoft introduced ACPI as favorite method for hardware controlling and system configuration.

There are however systems around incapable to meet the demanding hardware and software requirements ACPI imposes. These systems are handled by Windows as Standard PC.

Direct I/O introduced in version 4.3 the Serial Port Sharing feature which allowed to share serial ports between Direct I/O and the system.
This feature relies on some functionality only implemented in ACPI systems.

You can utilize Direct I/O on these systems too however you will not have the Port Sharing.

Follow the steps given below to change the Direct I/O installation:

  1. Login with Administrator rights
  2. Click Start->Run... and enter "CMD". Press Ok to run the command.
    A command line shell opens.
  3. Type "C:" and press the Enter key.
    The current drive now is C:
  4. Type "cd %systemroot%\system32" and press the Enter key.
    The current directory now is C:WINDOWS\system32
  5. Type "rundll32 directiocoinst.dll,Exec Uninstall" and press the Enter key.
    The uninstallation of the Serial Port Sharing component will be invoked.
    No output will be generated to indicate success or failure.
  6. Type "Exit" and press the Enter key.
    The command line shell is closed.
  7. Reboot your machine to have a clean startup.

Before Direct I/O will allow you to control the port it has to be disabled for Windows.
Follow the steps given below to disable a serial port:

  1. Open the Control Panel element System.
  2. Select tab Hardware.
  3. Click button Device Manager... to open the Device Manager
  4. Expand the group Ports (COM & LPT).
  5. Right-click the desired COM port and select Disable.
    Important: Do NOT select Uninstall!

If you should want to give back the port to Windows you could select Enable in the above step. The port won't be available for Direct I/O anymore.


This problem will be addressed in a future version of Direct I/O.

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Last modified: 2018-04-24.
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