The Software by msupi999

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									What	
  is	
  so)ware?	
  
  The	
  programs	
  that	
  run	
  on	
  a	
  computer	
  are	
  known	
  as	
  
   software.	
  
  E.g.	
  Word	
  processors,	
  Internet	
  Browsers,	
  Editors,	
  
   Database	
  Management	
  System,	
  Computer	
  Games.	
  
Opera0ng	
  System	
  
  When	
  you	
  turn	
  on	
  or	
  boot	
  your	
  computer,	
  a	
  program	
  
   called	
  the	
  operating	
  system	
  automatically	
  runs.	
  
  Operating	
  system	
  provides	
  an	
  interface	
  between	
  you	
  
   and	
  your	
  computer.	
  	
  
  It	
  manages	
  the	
  computer’s	
  resources	
  and	
  activities.	
  
  The	
  most	
  popular	
  operating	
  systems	
  are	
  Windows,	
  
   GNU-­‐Linux,	
  Unix	
  variants	
  and	
  MAC	
  OS	
  X	
  
Machine	
  Language	
  
  Each	
  computer,	
  or	
  more	
  specifically	
  each	
  CPU,	
  
     executes	
  instructions	
  encoded	
  in	
  its	
  own	
  unique	
  native	
  
     machine	
  language.	
  
  Machine	
  language	
  instruction	
  consists	
  of	
  a	
  sequence	
  of	
  
     bits.	
  For	
  example	
  
 	
   	
  10010010	
  	
  	
  00000001	
  	
  	
  00000001	
  	
  	
  10101101	
  

  Programming	
  in	
  machine	
  language	
  is	
  both	
  tedious	
  and	
  
  time-­‐consuming.	
  
High-­‐Level	
  Language	
  
  In	
  the	
  1960s,	
  the	
  first	
  high-­‐level	
  language,	
  FORTRAN,	
  
   was	
  invented.	
  
  FORTRAN	
  instructions	
  use	
  an	
  English-­‐like	
  syntax.	
  
  Today,	
  hundreds	
  of	
  high-­‐level	
  languages	
  are	
  available,	
  
   Fortran	
  2009,	
  COBOL,	
  Lisp,	
  Visual	
  BASIC,	
  C,	
  C++,	
  C#,	
  
   Java,	
  Perl,	
  Python,	
  PHP,	
  etc.	
  	
  
  A	
  typical	
  instruction	
  coded	
  in	
  a	
  high-­‐level	
  language,	
  
   such	
  as	
  BASIC,	
  might	
  be	
  
     	
   	
   	
  If	
  income	
  >	
  1000000	
  then	
  
        	
   	
  	
  	
  	
  	
  	
  	
  print	
  “You	
  are	
  rich!”	
  
Compiler	
  
  Before	
  a	
  program	
  that	
  is	
  written	
  in	
  a	
  high-­‐level	
  
   language	
  can	
  be	
  executed	
  on	
  a	
  particular	
  computer,	
  
   the	
  program	
  must	
  be	
  translated	
  into	
  the	
  machine	
  
   language	
  of	
  that	
  computer.	
  
  Translation	
  is	
  the	
  job	
  of	
  a	
  program	
  called	
  a	
  compiler.	
  

	
  	
  	
  	
  	
   	
                	
  	
  
                     	
     	
  C++	
  program                        	
              	
              	
  
                                                                                             C++	
  compiler	
            	
  Machine	
  language	
  program	
  
	
  	
  	
  	
  	
  	
                 	
         	
  	
  	
  	
  	
  (source) 	
                  	
              	
                	
               	
           	
  (target)	
  
Compiler	
  (cont.)	
  
  Once	
  a	
  compiler	
  translates	
  the	
  source	
  program	
  into	
  
   machine	
  language,	
  the	
  machine’s	
  CPU	
  can	
  execute	
  the	
  
   resulting	
  target	
  program.	
  
  A	
  programmer	
  can	
  write	
  just	
  one	
  program	
  and	
  
   translate	
  into	
  several	
  different	
  machine	
  languages.	
  	
  
  You	
  need	
  one	
  compiler	
  to	
  translate	
  your	
  program	
  into	
  
   a	
  machine	
  language	
  for	
  your	
  processor.	
  	
  
Java	
  
  Java	
  is	
  a	
  general-­‐purpose	
  language	
  developed	
  by	
  Sun	
  
     Microsystems	
  in	
  the	
  early	
  1990s.	
  
  Java’s	
  creators	
  identified	
  3	
  main	
  goals	
  for	
  their	
  new	
  
     language:	
  
 	
  -­‐	
  Platform	
  independence:	
  run	
  on	
  any	
  computer	
  
 	
  -­‐	
  Security:	
  should	
  not	
  be	
  susceptible	
  to	
  hackers’	
  code	
  
     and	
  viruses	
  
 	
  -­‐	
  Reliability:	
  should	
  not	
  crash	
  
Java	
  Virtual	
  Machine	
  
  In	
  order	
  to	
  make	
  Java	
  a	
  cross-­‐platform	
  programming	
  
   language,	
  Java’s	
  creative	
  team	
  designed	
  an	
  abstract	
  
   computer	
  implemented	
  in	
  software	
  called	
  the	
  Java	
  
   Virtual	
  Machine	
  ( JVM).	
  	
  
  The	
  machine	
  language	
  of	
  the	
  JVM	
  is	
  called	
  bytecode.	
  
  The	
  Java	
  interpreter,	
  which	
  is	
  part	
  of	
  the	
  JVM,	
  executes	
  
   each	
  bytecode	
  instruction,	
  one	
  by	
  one.	
  
  	
  Java	
  program   	
       Java	
  
                                   	
         	
     	
  Bytecode	
  
                                                                          JVM	
  
                               compiler	
  
Java	
  Virtual	
  Machine	
  
  The	
  bytecode	
  can	
  run	
  on	
  any	
  computer	
  that	
  has	
  
   installed	
  the	
  JVM.	
  A	
  Java	
  program	
  needs	
  to	
  be	
  
   compiled	
  into	
  bytecode	
  just	
  once.	
  
  Java	
  slogan	
  “compile	
  once,	
  run	
  anywhere”.	
  	
  

								
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