Tactical Software Tech Note


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Remapping COM Ports in Windows 2003 Server

Windows 2003 Server (SP1 and R2) has a command-line utility change.exe that re-maps COM ports in a user's Terminal Services session.

The following command:

change port COMx=COMy

redirects all COM port calls from COMx to COMy, where COMy can be a virtual COM port created by a Tactical Software redirector.

For example, consider a case of two Terminal Services users issuing change commands:

User 1: change port COM1=COM7

User 2: change port COM1=COM8

Both of these users can open COM1 at the same time and their applications will use Tactical virtual COM ports COM7 and COM8, respectively.

Note: The change command works only for COM ports and not with modem devices.  Two users can not simultaneously open a modem device on COM1 as the modem device is considered in use when the first user has it open. Therefore, the change command is useful only in applications running on Terminal Services client computers that directly open COM ports.

Older applications that can only use COM1-4 (or certain applications that are restricted to use only COM1-9) can now have the lower numbered COM ports mapped to higher numbered ones to allow more than 4 (or 9) Terminal Services clients to access the program at once.

The change command can also simplify the process of assigning users a unique virtual COM port on multi-user operating systems.  The change command can be run as part as a login script for each user to map COM1 to their own reserved virtual COM port.  Consequently, each user can use COM1 instead of a user-specific COM port (such as COM231) for each session.  The command for the login script in this case would be:  change port COM1=COM231