Secondary Memory and I/O
CPU Registers
  Addressable by "name".

  Byte or bit addressable.

  Very small amounts of data addressed at any time.

Primary memory.
  Byte or word addressable by address (numeric sequence in memory range).

  Moderate amount needed at any time. 

  Data needs to be accessed quickly.
    - exact byte or word  memory address.

  Data access may be random.
    - different data in different parts of memory.
    - mixed sequence of reads and writes 
    - flow of control breaks in code execution. 

  The program indicates an exact location and meaning for the data.

  All information stored in electronic gates*
    DRAM still electronic.    

I/O memory data/storage.
  Technology not native to the CPU.

  Quantities being accessed much larger. 

  Memory often addressed as a block of sequential bytes.

   Media (storage mechanism) highly variable.
     magnetic, optical (CD/DVD/Blu-ray), mechanical (punch), keyboard codes.

   Storage technology
     analog or digital. 

   Timing and boundary encoding 
     Encoding, carrier protocols, error protection.
    
    Large blocks of information.

    Large number of various sized "data sets".

    Size and diversity results in need for additional information (metadata)
      Need symbolic address (human friendly) which can efficiently
        be translated to standardized hardware addressing

      Storage data arranged in standard format (Sectors, clusters, etc.)  
        and accessed sequentially. Fairly standard on a particular media
        type (hard drives) but vary with media type.
         (DVD block size and encoding different from Hard drive)

      Streaming data may be arranged in frames.
        Size native to display or transport device.
        Also may involve issues of Isochronous nature (timing)

Input
  Keyboard : 1 - 10 bytes, intermediate.
  Mouse : serial - few bytes at a time.
  Touch pads 
  Sensors ( include A to D functions).
  Reading stored data.

Display

  CRT - cathode ray tube (monitors)
  OLED - organic light emitting diodes - cell phones, hand held devices.
  LCD - liquid crystal displays
     Streaming, time sensitive, depending on resolution, up to 40Gb/sec
  Printers - character based (old) or bit-mapped.

Secondary storage
  Depending on data use, may require strict time delivery (Movies, music)
  Or no error, e.g financial file.

  Tend to be very large in size.

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