Computer is an electronic machine that is used to solve different kinds of problems according to a set of instructions given to it. Computer consists of different units that perform various functions. All the operations of the computer are controlled by the program instructions. These program instructions are known as software. A system is a group of related components that make up a body to perform a specific function. Therefore computer system is defined as:

The computer along with various units and software that performs different activities in data processing are collectively known a computer system. A computer system is divided into two sub-systems:

1. Computer Software
2. Computer Hardware

Computer Software

A set of instructions given to the computer in machine code that tells the computer what to do and how to perform the given task of the user is known as computer software.

 OR

A set of instructions given to the computer in machine code to solve problems or to control different operations of the computer is known as computer software.

the sofware is developed in computer programming languages. You can not feel, touch or see software inside the computer memory.

Computer Hardware

The physical parts of a computer are known as computer hardware. You can touch, see and feel the hardware. The hardware consists of electronic circuits and mechanical equipment etc. used to perform various functions in the computer. The hardware components are:

1. Input devices
2. Output devices
3. Central Processing Unit (CPU)
4. Memory unit
5. Storage devices

Components of Computer

The internal architechtural design of computers differs from one system model to anohter. However the basic components and their functions are same for all computer systems. The construction of a typical comupter (PC) is very simple. It contains different components. Each components performs a specific function in the computer.

Input Devices

The devices that are used to enter data and instructions into the computer are called input devices or units. In old computers the punched card readers, paper tape readers were used as input devices. Now-a-days the most commonly used input devices are Keyboard and Mouse.

Output Devices

The computer processes the given input data and gives the output. The devices that are used to get output from a computer in readable from are called output devices. A number of output devices are available. Some commonly used output devices are video display units (VDU) and printers.

Central Processing Unit

Central Processing Unit is simply called as CPU. It is the main components of the computer and it is also called the Processor. The processor used in microcomputer is referred to as Microprocessor. CPU is considered the brain of the computer. It performs all operations of data according to program’s instructions. It executes the program instructions and tells other parts of the computer what to do. The CPU fetches instructions of program from main memory and executes them one by one. The CPU also has the ability to decide which instruction will be executed next. The speed of the CPU is measured in Mega Hertz (MHz) or Giga (or more).

The CPU is divided into two main prart of sub-units. These are:

1. Control Unit (CU)
2. Arithmetic Logic Unit (ALU)

1. Control Unit (CU)

The control unit is the most important component of the CPU. It controls and coordinates the activities of all the other units of the computer. The control unit is considered as the logical hub of the computer. It acts as a central nervous system for the other components of the computer.

For example the control unit receives the data and instructions from the input device and stores them in the main memory. It performs all these functions by issuing commands to the relevant unit of the computer.

The control unit also controls the execution of instructions given to the computer. It fetches the instructions and data from the memory unit. It decodes and executes the instructions one by one.

2. Arithmetic Logic Unit (ALU)

Arithmetic Logic Unit or simply ALU is another important component of CPU. It performs the arithmetic and logical operations on the data. When the control unit encounters and instruction related to perform arithmetic or logical operation on data, it passes that instruction to ALU.

• In arithmetic operations ALU performs the addition, subtraction, multiplication and division.
• In logical operations ALU compare the numerical data as well as alphabetic data. For example, it checks whether first number is greater than second, less than second or equal to second etc. It must be noted that some of the logical operations can be done on test data. For example when you want to search a word in a document., the CPU matches each word of the docum ent with the given word. Actually the ALU compares each word of document with the given word through relational equal operator (=).

The ALU consists of a number of registers and adder circuits. A register is a temporary storage device which holds data and instruction as long as it is being interpreted (decoded) and executed. When the data and instructions are fetched from main memory for processing, these have to be stored in one of the registers of the CPU.

Output and Output Devices – Monitor – Display Screen – LCD Monitor

The processed input data into a useful form is called output. When input data is processed, computer generates several types of output, depending upon the hardware and software used and the requirements of the user. The user views output on a screen, print it on the printer or hear it through speakers or headsets.

Therefore, output is normally classified as:

Softcopy Output

The output received on the display screen or in the audio or video form is called softcopy output. This kind of output is not tangible and it cannot be touched. The most popular and commonly used softcopy output device is display screen.

Hardcopy Output

The output printed on the paper is called hardcopy. The printers and plotters devices are used for this purpose.

Sound Output

The output received in the form of sound is called sound output. The speakers are most commonly used to receive the sound output.

An output device is a hardware component used to get output from the computer. A number of output devices are available. The commonly used output devices include display device (monitor), printer, speaker and headset, fax machine etc.

Monitors

The monitor is a popular and most commonly used output device. The monitor consists of a screen and the electronic components that produce the output on the screen for a temporary period. The output received on the screen is called softcopy. Most monitors used in personal computers display text, graphics and video information. Monitors can be divided into following categories.

Monochrome monitors

Monochrome means information displays in one color (such as white, green, black, blue, amber or gray) on a different color background, which is usually black. These monitors are usually used to display text only where you don’t need to see color graphics. Some PDAs and other mobile devices use monochrome monitors to save battery power.

Grayscale Monitors

Grayscale monitors are types of monochrome monitors. These monitors often use gray scaling to enhance the quality of graphics. They display the output using many shades of gray from white to black, which provide better contrast on the images. They are also used in handheld computers.

Color monitors

Color monitors are used to display output in different colors (i.e. from 16 colors to 16.7 million colors). Today, most of the personal computers use color monitors.