title: Why port 80 is used for server applications?
body: <p>I want to develop an enterprise application wherein each employee has a client application and there is a common server which has the server application. The client and server are basically exchanging information in the form of text, image files, zip files, etc. From my research I think TCP is the best protocol. But I do not understand how to assign port numbers. Here is what my understanding is so far.</p>
  
  <ul>
  <li>Client can have any random port selected automatically by OS. So I
  just need to query with OS for getting port number for client?</li>
  <li>Server port number has to be hard coded in server and client
  application.</li>
  <li>Server port number should always be 80. Why? Is it possible to have any other port number for server application? If yes how do I select it?</li>
  <li>What happens if the port number used by server is already being used by
  some other application on the server?</li>
  </ul>
  
  <p><strong>EDIT:</strong> Following are some of the articles/questions which gave me an impression that port 80 is the default port for the server.</p>
  
  <ul>
  <li><a href="https://stackoverflow.com/questions/3329641/how-do-multiple-clients-connect-simultaneously-to-one-port-say-80-on-a-server">How do multiple clients connect simultaneously to one port, say 80, on a server?</a></li>
  <li><a href="https://stackoverflow.com/questions/750604/freeing-up-a-tcp-ip-port">Freeing up a TCP/IP port?</a></li>
  <li><a href="http://computer.howstuffworks.com/web-server8.htm" rel="nofollow noreferrer">http://computer.howstuffworks.com/web-server8.htm</a></li>
  <li><a href="http://www.thomas-krenn.com/en/wiki/Check_TCP_Port_80_%28http%29_with_telnet" rel="nofollow noreferrer">http://www.thomas-krenn.com/en/wiki/Check_TCP_Port_80_%28http%29_with_telnet</a></li>
  </ul>