1.2 INTRODUCTION TO PC

 Specifically, a computer receives input (data or/and instructions) through the input devices (such as keyboard or mouse) process the data according to the specified instructions and then presents the output (results) in a readable form on its output device, i.e. either on its screen/monitor or on paper through the printer attached to it.

A simple analogy can be drawn between the sequence of operations performed by a computer and man to process data.

Suppose a student asks a teacher “what happens when 8 is multiplied by 6”. He receives the answer 40 from teacher. In the case of computer, this process can be described as follows: The teacher’s brain receives the question through his ears (analogous to a computer’s input device), processes the question with the help of his brain’s information processing and analytical ability (analogous to computer’s Central Processing Unit) and give the answer through the mouth (analogous to a computer’s output device). Further, just as the teacher can write down the answer on a sheet of paper or blackboard, the computer can also print the answer on a paper through a printer attached to it.

From the outside, a computer looks like:

The CPU resides inside a box known as the System unit, along with various support devices and tools for storing information. You can think of the system unit as a container for the CPU. The system unit case can either be short and wide usually underneath the screen (as in Figure-1) or it can be taller and narrow (Figure 2) and generally sits below of your desk.


Figure 2: CPU cabinet : A tower Case

The most notable things in a desktop PC are the screen (or monitor), keyboard, mouse, etc. However, from an architectural point of view, Figure 3 represents a true picture of a PC. 



Here memory (system) bus provides a communication between the system components (the CPU, printers, storage etc). The bus is a cable, which carries signals representing data from one place to another. For example, when data needs to be sent from memory to a printer, it will be sent via the system bus.

Personal Computers (PCs) are used in almost every working place such as school, colleges, offices; railways, banks, industries, hospitals, art and entertainment etc. The following Table illustrates various fields where we are using PCs.


Every modern computer system consists of three basic sections:

1. Input Device (i.e., Keyboard, mouse, scanner etc.)
2. Processor (or CPU):
• Control Unit (CU)
• Arithmetic-Logic Unit (ALU)
• Memory Unit
3. Output Device (Visual Display Unit (Monitor/Screen), Printer etc.)

The basic parts of a computer are shown in Figure 4.

• Input Devices such as Keyboard, Mouse or Scanner are used to enter
input (data or/and instructions), directly into the computer. 
• The CPU is like the human brain; it has a memory and just like there is
a faculty in the brain that regulates the functioning of all parts of the body; it has
a control-unit (CU), which controls the entire operation of a computer including
its input and output devices.
• Processing of data is done in the arithmetic and logic unit (ALU). It
performs Arithmetic and logic operations such as addition, subtraction,
multiplication, and division. Here, the word “Logic” is used because a computer
(unlike a calculator) has a capacity to do logical operations also, such as
comparing two numbers etc.
 
The function of a computer can be described as follows:
• The input is released under the direction of control unit (CU) from the input
device (say key board) to the memory unit.
• The control unit directs the requisite part of input to be sent to the ALU for
being processed.
• After the processing is over, control unit directs the ALU to release the
processed output to the memory.
• Then, finally, the output is released from the memory to the output device (say monitor/screen). Introduction to PC

Thus, a computer does mainly the following four functions:

1) Receiving Input : Accept information from outside through various input devices such as Keyboard, Mouse, etc.

2) Process Information : Perform arithmetic and logical operations on the information

3) Produce output : Communicate information to the outside world through output devices like monitor, printer etc.

4) Store information: Store the information in storage devices like, hard disk, pen drive etc.

These four functions are responsible for everything that computers do. Components of a computer system are given in Figure 5.


Fig. Components of a computer system

 

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