Check if port is used on windows machine

To check if a port is currently in use on a Windows machine, and then get some clue as to what’s using it, run the netstat program from a command console.

1. Start > Run
2. Enter cmd
3. In the command console enter:
   netstat -ano|grep portNumber
   This lists any processes where the port number is included somewhere on the line.
4. Look at the first number (in the second column). If this shows the port number after a colon, this means the port is currently being used.
5. Make a note of the number at the end of the line. This is the process ID (PID).
6. Run the ps program and grep for this PID:
   ps -ef|grep PID

Example

Here I was checking what was using port 4485.

C:\Documents and Settings\Administrator>netstat -ano|grep 4485
  TCP    192.100.61.161:4485    66.249.91.103:80       CLOSE_WAIT      2444

C:\Documents and Settings\Administrator>ps -ef|grep 2444
 Administrator 2444    - -   Aug 02   -   0:16 GoogleDesktopIndex      3    5

It turned out GoogleDesktopIndex was using that port.