The !-SlimServer-! opens and listens to a server socket.  It gets the port number from !-FitNesse-! via the command line.  The default is 8085 and it cycles through the next 10 ports to avoid collisions.  If 8085 is not convenient for you, you can set the !style_code(SLIM_PORT) variable to any port you like.  This variable can be defined on a page by page basis with !-!define-!, or it can be specified with !style_code(-DSLIM_PORT=xxxx) on the !style_code(java) command line, or it can be an environment variable.
if the port number configured is 0 then !-FitNesse-! will identify a free port with the help of the operating system.  
if the port number configured is 1 (default from Slim ''[0.5]'' onwards) than no port is openend and !-StdIn and StdOut-! is used for the communication. 