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Fundamental Chapter 1

 Q. What is Computer? Describe the functioning of computer with its block diagram?


Definition:-   A computer is a fast electronic device, processing the Input data according to the Instructions given by the Programmer/User and provides the desired information as an output.

It is an electronic, data processing machine that receives the input from some specific input devices, performs process, and produce output on some specific output devices.

A Computer System or its Architecture consists of following three elements:-
(1)       Input Unit
(2)       Output Unit

(3)       Central Processing Unit

Input Unit:-  Data and Instructions play an important role in the working of computer without data and instructions no computation can take place.  
            This is successful carried out by unit.  It establishes a connection between user and the computer system.
            Input Unit is a unit though which communicates with the computer.  It is a translator between the user the computer.  It converts the given into a computer acceptable form.
            The most common of Input devices keyboard, which resembles a typewriter.  The help of a keyboard, the user types data and instruction.  The other commonly Input devices are mouse, magnetic ink character reader, magnetic tape, magnetic disk, optical mark reader and optical character reader.

Input devices are divided into two categories:-

   Text Input Devices

   Cursor Control Devices
·        In text input devices the mainly used keyboard.
·        Cursor control devices are mouse, joystick, scanner etc.

In brief, the following functions are performed by the input unit:-
·        It accepts (reads) data from user.
·        It converts the instructions and data into computer acceptable form.
·        It passes the converted instructions and data to the computer for processing.

Output Unit:-  Since computers work with binary code, the results produced are also in binary form the basic function of the output unit therefore is to convert these results into human readable form before providing the output through various output devices like terminals, printers etc.

Output device can be classified into two types:-

(1)              Hard Copy Devices

(2)              Soft Copy Devices

 Hard Copy Devices:-  These are those devices that provide the output in permanent form.  User can't change them and we can see them without the help of any machine. These devices are printers, plotters etc.

Soft Copy Devices:-  This comes in category when power is switched off, information are lost information is on display till power is ON. We can make change in this and we cant able to access them without the help of any machine.  Visual display unit(Screen) comes under this category.  This unit is based for displaying results, which are produced after processing of data.

In brief, the functions of the Output units are:-
·        To accept the results processed by CPU which are in coded form.
·        To convert coded results to human acceptable form.
·        To produce the results to users.

Central Processing Unit:-  The main brain of a computer system s the central processing unit (CPU).  The data and instructions that are entered into the computer system are fed into the CPU before the final results are displayed on the Output Unit.  The CPU stores the data and instructions, does all the calculations and problem solving, and also controls the functions of all other units.
The CPU consists of the following Units:-

(1)                          Memory Unit or storage Unit
(2)                          Arithmetic & Logical Unit (ALU)
(3)                          Control Unit

Memory Unit:-  The data and instructions that are entered into the computer system with the help of input units must be stored inside the computer before processing starts.  Also the results produced by the computer after processing must be stored inside the computer.  The memory unit is responsible for storing data, instructions and results.  The memory unit consists of a large number of cells, each capable of storing one unit of information (word).  The cells are also called storage locations.

Memory Unit has four major logical areas:-

Input Storage Area:-  The Input does not straight away go to the processor.  It is first stored in this area till the processor asks for it.

Working Storage Area:-  Working Storage Area is like a sheet of scratch paper.  When the data is being processed, there are some intermediate results that are not required as Output but are required to obtain the Output.  Such results are stored in working storage area.

Input Storage Area:-    The final output don’t take by the output devices immediately until they are ready to receive it.  Thus an ‘output storage area’ holds the finished results until they are released on the output device.

Program Storage Area:-  The primary storage also contains a program storage area.  The instructions for data manipulation are stored in this area.

Following are the main functions of memory unit:-
(1)   It stores data and instructions received from the input unit before processing starts.
(2)   It stores the intermediate result of processing.
(3)   It stores the final results of processing, before these results are sent to output unit.

Arithmetic & Logical Unit:-  This unit performs all the basic arithmetic operations like addition, subtraction, multiplication, division and also logical operations such as comparison of numbers etc.  the ALU is responsible for actual execution of instructions during processing operation.  The data and instructions that are stored in memory unit are transferred into ALU for processing when needed and transferred back to memory when processing is over.  After the completion of processing, the final results are stored in memory before sent to the output unit.  ALU also consist a number of small storage locations, termed as registers.  These registers are of very small capacity and contains the data and instructions which are to be executed next.

Following are the main functions of ALU:-

·              It operates on data available in main memory.
·       It caries out all arithmetic operations like addition, subtraction, multiplication and division.
·              It caries out all logic operations like comparison, selection and merging of data
·              After processing the data, it sends back the processed data to main memory.

Control Unit:-  The control Unit in every computer is the supervising element.  It does not perform any processing but acts as a central control system for all other components of a computer system.  This unit maintains the exact sequence in which the instructions are to be executed and directs the operations of the entire computer system.  It co-ordinates all the activities of various elements of computer system skill.  It is termed as heart of computer as in controls all hardware operation.

Functions of control unit are:-
·              It gives command to transfer data from the input device to memory and from memory to arithmetic & Logical Unit.
·              It transfers the results from memory to Output Unit.
·              It stores the program in memory, takes instruction one by one, interprets them and issue appropriate signals to the other units of computer to the other units of computer to execute them.

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