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(A) What is computer? Describe computer hardware. Explain one input and one output device.

Computer
Computer is an electronic machine used to solve different problems according to a set of instructions given to it. A computer can accept data, process data into useful information and store it for later use. It can be used for different purposes. People use computers to solve different problems quickly and easily.

Computer Hardware
The physical components of a computer are called hardware. You can touch, see and feel hardware. The Input/Output devices (like mouse, keyboard, printer, Monitor), CPU, Memory unit etc are examples of computer hardware.

Input Device
The data and instructions are given to the computer as input. The input device is used to give input to the computer. For example Keyboard, Mouse etc.

Keyboard
Keyboard is the most commonly used input device. It is mostly used to enter text and numeric type data into the computer. The buttons on the keyboard are called Keys. The keyboard contains keys for all alphabetic, characters, numeric digits, and special characters. It also contain some special keys known as functional keys. A standard keyboard contains more than 100 keys and also known as QWERTY keyboard. Because the first six leftmost keys on the top row of alphabets are Q, W, E, R, T and Y.

Output Device
The processed data is also known as output. The output device is used to get output from the computer. It gives processed data or results in a form that a user can understand. The commonly used output devices are monitors, printers and speakers.

Printers
Printers are the most commonly used output devices. They are used to produce the hardcopy of the output. The output printed on the paper is called hardcopy. The output may be in the form of characters, symbols and graphics. A printer is connected to a parallel port of system unit by a cable. The parallel port is also called LPT1. LPT1 stands for line printer 1.

Types of Printers
The main types of printers are as follows:
1.Character printers
2.Line printers
3.Page printers

(B) What is the purpose of Instruction Register (IR) in the computer system?

Instruction Register (IR)
In a computer system, when an instruction is fetched from main memory, it is stored in the Instruction Register. The control unit takes instruction from this register, decodes and executes it by sending signals to the appropriate component of computer to carry out the task.

(C) Write a short note on Main Memory.

Main Memory
Main memory is where programs and data are kept when the processor is actively using them. When programs and data become active, they are copied from secondary memory into main memory where the processor can interact with them. A copy remains in secondary memory.Main memory is intimately connected to the processor, so moving instructions and data into and out of the processor is very fast. Main memory is sometimes called RAM(Random Access Memory).

(D) Describe Control Unit (CU).

Control Unit is the most important part of CPU. It acts as supervisor of the computer. It controls and coordinates the activities of all the other units of the computer. For example, it receives the data and instructions from input devices and store them in the main memory. CU 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.

(E) Define the purpose of the following register in Computer Systems:
(i) Data Address Register (DAR)
(ii) Instruction Register (IR)

Data Address Register (DAR)
It is also known as Memory Address Register . It holds the memory addresses of data and instructions. This register is used to access data and instructions from memory during execution phase of an instruction. Suppose CPU wants to store some data in the memory or to read the data from memory. It places the address of the required memory location in the MAR or DAR.

Instruction Register (IR)
Once an instruction is fetched from main memory, it is stored in the Instruction Register. The control unit takes instruction from this register, decodes and executes it by sending signals to the appropriate component of computer to carry out the task.