When a device completes the command in a message, it will return the
message to the message port specifed as the reply port in the message.  A
message port is obtained by calling the CreateMsgPort() or CreatePort()
function.  You must delete the message port when you are finished by
calling the DeleteMsgPort() or DeletePort() function.

If your application needs to be compatible with pre-V36 versions of the
operating system, use the amiga.lib functions CreatePort() and
DeletePort(); if you require V36 or higher, you may use the Exec ROM
functions CreateMsgPort() and DeleteMsgPort().