>Cant we do like running different applications on different ports of same Web Server.
What do you mean by that? Please explain more precisely.
Of course you can run one program per port - each port can be served by a different program (thats precisely the idea of different ports).
For example, port 80 is the standard port for Apache or any other webserver software, port 21 is standard port for FTP programs, port 25 is standard port for sendmail program and so on.
If you want to run the SAME program on TWO different ports (for example Apache), you have to start TWO DIFFERENT instances of the program in order so serve both ports. Apache cannot serve two ports in one instance.