Pulse Code Modulation ( PCM )

by ASR Blogger in , ,

This method used to convert Analog signal to Digital Signal.There are 3 steps in this process.


1.Sampling - In this step, Input signal divides into small pieces (samples).
   To decide how many samples we should get, we use sampling theorm.
   




Sampling  Rate = 2 X Highest Frequency






2.Quantizing
The samples are divided into many discrete levels.

Then each sample is numbered according to their corresponding level.



3.Encoding
 After quantizing the corresponding level it is to be represented in some manner. 
 If  the level is 50, it can be represented as,

Second Generation - 1960-1964

by ASR Blogger

*Transistors replaced vacuum tubes and it was a vast improvement over the vacuum tube.
*Transistor was invented in 1947 but used in computers in the late 50s.
*Computers become smaller, faster, cheaper, more energy-efficient and more reliable.
*One transistor replaced the equivalent of 40 vacuum tubes
 
 
Transistors
             Transistors were made of solid material, some of which is    silicon, an abundant element found in beach sand and   glass. Therefore they were very cheap to produce.

          * Conduct electricity faster and better than vacuum tubes.
          * Much smaller and gave off virtually no heat compared to   vacuum tubes.  
 
       *Replaced Machine language with the Assembly language.
      *Early versions of COBOL and FORTRAN.
      *Still relied on punched cards for input and printouts for output.
      *Transistor still generated a great deal of heat and subjected to computer damages.
 

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