Point to point (sometimes referred to as a port)
    Connects a single device to the system.

    Addressing not needed to recognized connected device.
      Primary addressing established when selecting port by controller.

    Dedicated purpose - designed for specific 'device'.
      Secondary addressing for functions or data architecture on slave device.
        e.g  LBA or c/h/s of sectors on hard drive.

      Minimal controls and protocol. - Only those for specific devices.

      May provide only uni-directional data movement.
        Early parallel printer ports - data just flowed from PC to printer.

    Multi-purpose - designed to 'recognize' a variety of possible devices.
      Primary addressing established by controller but may also include
        routing information in transmitted information
          USB, Ethernet

      Broad range of control support and protocol - for dealing with a 
        variety of 'devices'.
    
      Bi-directional. May use paired unidirectional lines or may allow
        lines to transmit in both directions.


    Examples of dedicated purpose ports.

      Parallel printer port (IEEE 1284) - printers, zip drives.
      
 
      AGP - Advanced Graphics Port - (2004) Video cards.
        Interface Video card to mother board.
        Modified PCI interface.

      Video ports
        VGA
        

        DVI
        

        HDMI
        
        

        Display-Port - video.
        
 
        Mini Display-port
        
          Uses packetized information - allowing expansion of protocol at
            software level.

      Keyboard/Mouse  * largely replaced by USB.
        XT/AT Keyboard port.

        PS/2 - keyboard/mouse ports.
        

    General purpose port.

      Wide range of controls and broad protocol.

      Bi-directional data transfer or 'lanes' with paths in both directions.

      Common ports
        PCI-e - hardware point to point. Software multi-port.
          internal - but external extension available.
          
          * bottom slot is standard PCI interface.

        SATA - storage device interface, Hard drives, CD, DVD, Blu-Ray, SSD
          Limited protocol. internal.
          eSATA - external interface.


        USB - hardware point to point. Software multi-port. External.
          Requires master.

        IEEE 1394 (Fire-wire or i.LINK) - alternative to USB. External.
          Initially more advanced, built on SCSI protocols. 
          Uses arbitration - any device may be master.
          

        Thunderbolt - combination of Display Port and PCI-e. External.
        

        ISA Serial port (RS232) - 1980s, modems, printers. External
          Very limited protocol but very flexible. Fairly standardized
          physical layout.
        

 
     * Some of these can use hub or daisy chain implementation allowing a
       single port from controller to multiple devices.
       Addressing usually implemented via software packets.


  Multi-point Bus - physically connects multiple devices.

    Addressing - broadcast to each device, requiring additional decoding
      or selection at device or port interface.

    Bi-directional data movement.

    Generic controls for unknown devices.
      Timing, handshaking, data direction.

    Common buses.
      XT, AT bus. Internal.
      PCI bus. Internal.

      Parallel ATA - hard drive/Optical drive interface. Internal.

      IEEE-488 GPIB. External.
        

  Networked
    Broadcast.

    Point to point with routing to further points.

    Addressing.
      Source/destination address.
      Source/destination ports.

    Address, data, and control implemented at the software/packet level.

    Often missing power bus.

    Can span much greater distances that system level buses.

  * Port also refers to the physical connection and can exist on
     multi-point connections, USB, IEEE 1394 (Fire-wire), SCSI