Detecting Windows NT Serial Ports

 Last reviewed: March 24, 1997
Article ID: Q100372
The information in this article applies to:
  • Microsoft Windows NT operating system version 3.1
  • Microsoft Windows NT Advanced Server version 3.1
  • Microsoft Windows NT Workstation versions 3.5, 3.51, and 4.0
  • Microsoft Windows NT Server versions 3.5, 3.51, and 4.0

Windows NT manages serial (COM) ports somewhat differently from the way Windows 3.1 does. In Windows 3.1, you can observe and configure all the COM ports from Ports in Control Panel. In Windows NT, only unused COM ports are displayed in Control Panel. For example, if a mouse is connected to COM1, COM1 is not available in Control Panel, nor is it listed. To check a COM port and perform any trouble-shooting steps, you need to use Registry Editor.

Finding Serial Ports in Registry Editor

To determine what is using a COM port, from Registry Editor go to the following subkey: 

   \HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION\System
   \MultifunctionAdapter\0\SerialController\...
Note: If you have an EISA type computer, MultifunctionAdapter will be EisaAdapter.

Each COM port is stored in one of the numbered subkeys. If you have two COM ports, COM1 and COM2, you would find them stored under 0 and 1, respectively.

If a mouse is using a COM port, you will find a PointerPeripheral subkey under the serial ports subkey. For example: If you have a mouse on COM1, you would see the following: 

   ...\SerialController\0\PointerPeripheral
If PointerPeripheral is absent, then the serial port is in use by some other device.

Additional Differences in Windows NT Control Panel

You might notice an additional difference in Windows NT Control Panel. If you select a COM port, choose Settings, and then choose Advanced, the following message may be displayed in a dialog box: 

   There are no user configurable Advanced I/O parameters for this
   COM port.
This means that Windows NT has obtained all the information it needs for the port from NTDETECT.COM (or OSLOADER.EXE on RISC-based computers). This ensures that redundant or incorrect information is not entered.

Additional query words: prodnt
Keywords : kbhw nthw
Version : 3.0 3.5 3.51 4.0
Platform : WinNT

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Last reviewed: March 24, 1997
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