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On Windows XP, how can we find out which program is currently using port COM1? Some program will try to grab it at startup, and others may not release it at shut down.

When an application exits in Windows XP, Windows will release resourses that the program had, like COM1 even if the program did not release COM1 itself.

If you want to find out which program has COM1, then shut down the running applications one at a time until your program that tries to open COM1 is able to succeed.

Robert Scott
Real-Time Specialties
Embedded Systems Consulting

Try http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx