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What is a computer by bigbro22

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									Lecture 1
Introduction



    Input             Computer               output




              What is a computer?
   A computer accepts external input , processes the
   data, and produces certain output .
   An algorithm is a \recipe" for processing information
   | a series of steps that transform input to output.




                          1
LECTURE 1.   INTRODUCTION                         2


1.1 Basic Computer Architecture




                Control   Arithmetic   I/O
                 Unit        Unit      Unit




Input                                         output




                           Memory




                          Secondary
                           Storage
LECTURE 1.   INTRODUCTION                                     3



              Key Elements in a Computer
      Input Unit:
        { Obtains information (data and programs) from
         various input devices, such as keyboard and disk
         drive.
      Output Unit:
       { Places processed information onto various output
         devices, such as screen or printer.
      Memory Unit:
       { Retains information entered from the input unit.
       { Stores programs.
       { Stores intermediate results during processing.
      Arithmetic and Logic Unit (ALU):
       { Performs actual calculations and comparisons.
      Control Unit:
       { Supervises and coordinates the entire operations
         of a computer.
      Secondary Storage:
       { A device, such as tapes or disks, for storing pro-
         grams or data that are not actively being used by
         other units.
LECTURE 1.     INTRODUCTION                                                        4




                       0 1 0 0 0 0 0 1                (represents character ‘A’)




                                                bit
 0000           0001     0002            0003
        byte
 0004


                  ......
                      Memory
                                ......




         Memory Organization | Bits & Bytes
        In the lowest level, computers understand only 0's and
        1's.
        Computer memory stores a sequence of 0's and 1's.
        Each such storage unit is called a bit .
        Eight bits are grouped together to form a larger stor-
        age unit called a byte .
        Each byte has a unique address for identi cation.
        Computer memory can thus be viewed as a series of
        bytes.
LECTURE 1.        INTRODUCTION                                         5


1.2 Computer Programming

                       Computer Programming
             The job of a programmer is to design a complete and
             precise set of instructions for a computer to carry out
             a particular problem-solving task.
             A programming language is a medium for program-
             mers to express instructions to the computer.
             Do we need to write our programs in 0's and 1's?!



High Level                        Executable                  Answer
                      Compiler                   Computer
Language


                                                   Input




                High Level Programming Languages
             Fortran, Cobol, Pascal, Modula-2, Ada, C, Smalltalk,
             C++, Prolog, Lisp, Perl, Java, Visual Basic, ...
             Compilation: High level languages require the use of a
             compiler to translate into machine executable codes.

2 End.

								
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