Bus basics and function
  Bus -  A set of related paths interconnecting 2 or more devices.
 
  Used to connect logic units or devices.
    Internal to CPU.
      Data-paths.

    Between CPU and other logic circuits on motherboard.
      ISA bus - implemented most of the CPU lines/signals on the motherboard.

      Front-side bus, back-side bus circa 1990s-2000s
        Back-side bus - dedicated interface to cache memory. 
        Front-side bus - interface to routing bus controller hub.

      Intel Quick-Path Interconnect/HyperTransport  # current
        Bus controller that provides collection of real/virtual point to point
        direct interfaces between CPU and external logic 
        implemented with packet driven communication.

      PCI/PCIe bus - Peripheral Component Interconnect

    Between computer and external devices.
      ATA-IDE/SATA - disc access bus  
        Advanced Technology Attachement-Integrated Drive Environment

      SCSI/SAS - (small computer system interface)
        external devices, discs, printers, plotters, etc.
        Small Computer Systems Interface
 
      USB, Fire-wire, eSATA, Ethernet (Network Accessed Storage),

      Bluetooth, WiFi - wireless, broadcast.

    Between systems (anywhere).
      Ethernet, WiFi, "Internet"

Bus protocols.
  Set of rules that describe the behavior/properties of the bus.  
    Implemented at the OS and device driver level.
    Needed to allow designers/manufacturers to produce standardized circuits. 

  Open vs. Proprietary (sometimes not even published).

Protocol specifics include:
  Number of lines for particular functional unit (address, data, etc.)
    
  Physical layout of the controller/bus interface.

  Physical vs. Virtual implementation.

  Speed/timing of communication across bus lines, lengths and limits.

  Voltage levels.

  Frame or packetized.

  Types of control available.

  Encoding standards of information passed.