Maximum Number of Serial Com Ports on a Windows Computer

Updated Mar 12, 2018

Reported In

Hardware

  • GPIB-RS232

Driver

  • NI-VISA

Operating System

  • Windows

Issue Details

What is the maximum number of Serial COM ports I can have on my computer using National Instruments' Serial Products?

Solution

The maximum number of COM ports is dependent on both the operating system (OS) and the serial driver. The maximum number of serial ports that NI-VISA currently supports on any platform is 256. COM port limitations are listed below:
  • On Windows NT, NI-VISA limits the number of COM ports to 99. 
  • On Windows 95, 98, 2000, and XP the OS and NI-VISA limit the number of COM ports to 256.
  • On Windows 7, 8, and 10, NI-VISA limits the number of COM ports to 256. 
  • For the serial ENET products on Windows NT and 2000, NI-VISA limits the number of COM ports to 256. 

Additional Information

Because of the constraints on the number of serial ports from the OS and the serial driver, the number of National Instruments serial cards that you can use in your system is limited. When selecting the appropriate serial card(s) to use, ensure that the total number of ports on your cards is less than the maximum number of COM ports for your system.  

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