Data transfer and storage problem.

Situation:
  Data in primary storage exists as discrete addressable storage.

  Quantity of data being accessed fairly small.

  Data stored and accessed using electronic switches.
    Very fast and provide discrete units. Each bit cell is unique
      and addressable.

  Systems have a dedicated clock line providing synchronization
    and boundary checks for transmitted bits.

  *

  Data in secondary storage or being transmitted 
    Tend to have boundaries much less distinct.

  Transmission:  

    Electrical:    different voltage/current levels.
      * Think of water faucet and hose. 

    Optical:       light pulse 
      * best for discrete transmission 
         but requires conversion to electrical for switching or fanout.

    Electro-magnetic: frequency distortion or phase shift over radio waves.
                      Analog carrier.
         
  Storage: 
    Magnetic:     magnetized zones (analog) in alternate directions.
 
    Optical:      reflective and non-reflective. 

    Electronic    large banks of Flash ROM.  
                  Electronic, but requires sugnficicant overhead.

  Transmitted/stored data requires alternative ways 
    to provide clocking/boundary information.

  Cost effective storage media man not be electronic. 
     Magnetic.
     Reflective surface.

  Size of data several magnitudes larger that 'primary' memory,
    requires working with larger block size (> bit, byte, word).
    Requires additional addressing information (meta-data).
       
Data vs. Carrier
   Analog and Digital  (4 combinations).

   Data 
     Analog :  movies, audio, wind speed, etc. 
     Digital : programs, text files, etc.

   Carrier
     Analog : Radio/TV, Wi-Fi, Magnetic (tape drive, hard drives).
     Digital : system bus, fiber optics (pulse), CD, DVD.