Source : Free On-Line Dictionary of Computing

SPX
     
        1.  {Sequenced Packet Exchange}.
     
        2.  A graphics program for the {Atari} microcomputer.
     
       
     {(ftp://src.doc.ic.ac.uk/computing/systems/atari/umich/Graphics/spx_v18.lzh)}.
     
        3. {Simplex}.
     
        (1997-03-04)

spx
     
         The {filename extension} for {Screen
        Peace} eXtension files.
     
        (1995-03-14)