2 instance of postgres service running against same db files?

  Can I have 2 instance of postgres service running against same db???. I meant 2 machine or the same machine with a 2 running executing postgres process (if it is in the same machine, then through different ports), working with the same db files,  may be in a shared storage or any common mounted file system. Any other variant? How?

 Im sorry because of my english. I speak spanish.

 thanks...