Class 11 Information Technology (802)

Unit 1: Computer Organization

Introduction to fundamentals of Computer and its use

A computer is an electronic programmable device that accepts data as input, processes it according to a set of instructions, stores it, and produces meaningful information as output.

A computer can perform millions or billions of operations in a very short time. Modern computers are used in almost every field, including education, banking, healthcare, business, communication, science, transportation and entertainment.

Basic Working of a Computer

The fundamental working of a computer can be represented as:

Input → Processing → Output

A computer may also store the data and instructions for future use.

Uses of Computers

Computers are used in almost every area of modern life.

Characteristics of a Computer

Computers have several characteristics that make them useful for performing different types of tasks.

1 High Speed

A computer can perform a very large number of calculations in a very short period of time.

For example, a computer can process thousands or millions of instructions in seconds.

Example:
Calculating the marks and percentage of thousands of students can be done quickly using a computer.

2 Accuracy

Computers generally produce highly accurate results when the data and instructions supplied to them are correct.

This is sometimes described by the principle:

Garbage In → Garbage Out (GIGO)

If incorrect data is entered, the computer may produce an incorrect result.

3 Diligence

Unlike humans, computers do not become tired or bored after repeatedly performing the same task.

A computer can perform the same operation thousands of times with consistent performance.

Example:
Generating monthly salary slips for employees.

4 Large Storage Capacity

Computers can store enormous amounts of data.

Data may be stored using:

• Hard Disk Drive (HDD)

• Solid State Drive (SSD)

• Pen Drive

• Memory Card

• Optical Disk

• Cloud Storage

5 Automation

Once a computer program and required data are supplied, many tasks can be performed automatically without continuous human intervention.

Example:
An automatic billing system can calculate the bill, taxes and final amount after the required products are entered.

6 Versatility

A computer can perform many different types of tasks.

For example, the same computer can be used for:

• Preparing documents

• Watching videos

• Programming

• Internet browsing

• Data analysis

• Graphic designing

• Online learning

• Banking

7 Reliability

Computers can perform repetitive operations consistently and reliably when their hardware, software and input data are correct.

8 Multitasking

A computer can handle multiple tasks or applications during the same period.

Example:

A user can:

• Play music

• Browse the Internet

• Type a document

• Download a file

at the same time.

9 No Intelligence of Its Own

A computer does not normally think or make decisions like a human being. It follows the instructions provided by software and programs.

Artificial Intelligence can make systems capable of sophisticated decision-making, but such systems still operate through programmed algorithms and trained models.

Components of a Computer

A computer system consists of several major components.

The major functional units are:

1. Input Unit

2. Central Processing Unit (CPU)

3. Memory/Storage Unit

4. Output Unit

The CPU itself contains important components such as:

• Arithmetic Logic Unit (ALU)

• Control Unit (CU)

• Registers

1. Input Unit

The Input Unit is used to enter data and instructions into a computer.

It accepts data from the user and converts it into a form that can be processed by the computer.

Examples of Input Devices

• Keyboard

• Mouse

• Scanner

• Microphone

• Webcam

• Touchscreen

• Barcode Reader

• Joystick

Functions of Input Unit

1. Accepts data from the user.

2. Converts data into machine-readable form.

3. Sends the data to memory or CPU for processing.

2. Central Processing Unit (CPU)

The Central Processing Unit (CPU) is commonly called the brain of the computer because it performs processing and controls the activities of other components.

The CPU consists mainly of:

2.1. Arithmetic Logic Unit (ALU)

The Arithmetic Logic Unit (ALU) performs arithmetic and logical operations.

Arithmetic Operations

• Addition

• Subtraction

• Multiplication

• Division

• Increment

• Decrement

Logical Operations

• Comparison

• Greater than

• Less than

• Equal to

• AND

• OR

• NOT

Example

Suppose:

A = 20
B = 10

The ALU can perform:

20 + 10 = 30
20 - 10 = 10
20 × 10 = 200
20 > 10 = TRUE

2.2. Control Unit (CU)

The Control Unit controls and coordinates the activities of the computer.

It does not normally perform arithmetic calculations itself. Instead, it directs other components regarding what operation should be performed and when.

Functions of Control Unit

• Fetches instructions from memory.

• Decodes instructions.

• Controls execution of instructions.

• Coordinates CPU, memory and input/output devices.

• Sends control signals to various components.

The Control Unit acts like a manager or coordinator of the computer system.

2.3. Registers

Registers are very small and extremely fast storage locations inside the CPU.

They temporarily hold:

• Data

• Instructions

• Memory addresses

• Intermediate results

Registers are faster than main memory.

Examples of Registers

Depending on processor architecture, registers may include:

• Program Counter (PC)

• Instruction Register (IR)

• Memory Address Register (MAR)

• Memory Data Register (MDR)

• Accumulator

• General-purpose registers

3. Memory Unit

Memory is used to store data, instructions and results.

Computer memory can broadly be divided into:

Primary Memory

Primary memory is directly accessible by the CPU.

Examples:

• RAM

• ROM

• Cache Memory

Secondary Storage

Secondary storage is used for long-term storage.

Examples:

• HDD

• SSD

• Pen Drive

• Memory Card

• Optical Disk

3.1. RAM

RAM stands for Random Access Memory.

It temporarily stores programs and data currently being used by the computer.

RAM is volatile memory, which means its contents are normally lost when the power is switched off.

Example

When you open a document, the operating system loads the required data into RAM so that the CPU can work with it.

3.2. ROM

ROM stands for Read Only Memory.

It stores information that is generally retained even when the computer is switched off.

ROM is non-volatile memory.

It is commonly used for storing firmware and boot-related instructions.

3.3. Cache Memory

Cache is a small and very fast memory located close to or integrated with the CPU.

It stores frequently used data and instructions so that the CPU can access them more quickly.

A simplified hierarchy is:

Generally, the closer the storage is to the CPU, the faster it is and the smaller its capacity tends to be.

4. Output Unit

The Output Unit presents the processed information to the user.

Examples of Output Devices

• Monitor

• Printer

• Speakers

• Projector

• Headphones

• Plotter

Functions

1. Receives processed results.

2. Converts them into a human-readable form.

3. Presents the result to the user.

Task Execution

Suppose a user enters:

15 + 25

using a keyboard.

Step 1 – Input

The keyboard sends the entered data to the computer.

Step 2 – Storage

The required data and instructions are placed in memory.

Step 3 – Fetch

The CPU fetches the appropriate instruction.

Step 4 – Decode

The Control Unit determines that an addition operation is required.

Step 5 – Execute

The ALU performs:

15 + 25 = 40

Step 6 – Store

The result may temporarily be stored in a register or memory.

Step 7 – Output

The result 40 is displayed on the monitor.

Functions of Various Components

CPU and Its Functions

The CPU performs several important functions.

1. Instruction Processing

The CPU reads and processes instructions provided by programs.

2. Arithmetic Operations

The ALU performs calculations such as addition, subtraction, multiplication and division.

3. Logical Operations

The CPU performs comparisons and logical operations.

4. Control

The Control Unit coordinates the activities of different computer components.

5. Data Movement

The CPU manages the movement of data between registers, memory and other components.

6. Temporary Storage

Registers provide extremely fast temporary storage during instruction execution.

Difference Between CPU, ALU and CU

Hardware and Software

A computer system consists of both hardware and software.

Hardware

Hardware refers to the physical components that can be seen and touched.

Examples:

• Keyboard

• Monitor

• CPU

• RAM

• Mouse

• Printer

• SSD

Software

Software is a collection of programs and instructions that tells hardware what to do.

Examples:

• Windows

• Linux

• Android

• Microsoft Word

• Web browsers

• Programming applications

Relationship

          SOFTWARE
              ↓
       Gives Instructions
              ↓
          HARDWARE
              ↓
       Performs the Task

Hardware cannot perform useful tasks without appropriate software, and software requires hardware to execute.

Data and Information

Data

Data refers to raw facts and figures.

Example:

85, 72, 91, 64

These values by themselves may not provide complete meaning.

Information

Information is processed and organized data that has meaning.

Example:

Average Marks = 78%

Thus:

Data + Processing = Information

Important Terms

Computer

An electronic programmable device that accepts input, processes data, stores information and produces output.

CPU

The primary processing and control unit of a computer.

ALU

The part of the CPU responsible for arithmetic and logical operations.

CU

The part of the CPU responsible for controlling and coordinating operations.

RAM

Volatile primary memory used to temporarily store active data and programs.

ROM

Non-volatile memory used to store information such as firmware.

Register

Very fast storage location inside the CPU.

Input

Data supplied to a computer for processing.

Output

Processed information produced by a computer.

Storage

The process of saving data and information for future use.

Quick Revision

Remember the basic computer cycle:

Input → Process → Output → Storage

Remember the CPU components:

CPU = ALU + CU + Registers

Remember instruction execution:

Fetch → Decode → Execute → Store

Remember the major buses:

Data Bus + Address Bus + Control Bus

Important Exam Questions

Very Short Answer Questions

Q1. What is a computer?

A computer is an electronic programmable device that accepts data as input, processes it according to instructions and produces useful information as output.

Q2. What is CPU?

CPU stands for Central Processing Unit. It performs processing operations and controls the activities of a computer.

Q3. What is ALU?

ALU stands for Arithmetic Logic Unit. It performs arithmetic and logical operations.

Q4. What is CU?

CU stands for Control Unit. It controls and coordinates the activities of different components of a computer.

Q5. What is RAM?

RAM stands for Random Access Memory. It is volatile primary memory used for temporarily storing active programs and data.

Q6. What is ROM?

ROM stands for Read Only Memory. It is non-volatile memory used for storing information that needs to be retained when power is switched off.

Q7. What is a register?

A register is a small, very fast storage location inside the CPU.

Short Answer Questions

Q1. Write any five characteristics of a computer.

Five characteristics are:

1. High speed

2. Accuracy

3. Diligence

4. Large storage capacity

5. Versatility

Q2. What are the main functions of the Control Unit?

The Control Unit:

• Fetches instructions.

• Decodes instructions.

• Generates control signals.

• Coordinates CPU and other components.

• Controls the sequence of operations.

Q3. What is the function of ALU?

The ALU performs arithmetic operations such as addition, subtraction, multiplication and division and logical operations such as comparison and Boolean operations.

Q4. Explain the Fetch–Decode–Execute cycle.

The CPU first fetches an instruction from memory, then decodes it to determine the required operation and finally executes the operation. The result may then be stored.

Long Answer Question

Explain the major components of a computer.

A computer consists of four major functional units:

Input Unit:
Accepts data and instructions from the user.

Memory Unit:
Stores data, instructions and intermediate/final results.

CPU:
Processes instructions and controls computer operations. It consists mainly of ALU, Control Unit and registers.

Output Unit:
Presents processed information to the user through devices such as monitors, printers and speakers.

One-Minute Revision Sheet

COMPUTER
   │
   ├── INPUT
   │     ├── Keyboard
   │     ├── Mouse
   │     └── Scanner
   │
   ├── PROCESSING
   │     └── CPU
   │          ├── ALU
   │          ├── CU
   │          └── Registers
   │
   ├── MEMORY
   │     ├── RAM
   │     ├── ROM
   │     └── Cache
   │
   └── OUTPUT
         ├── Monitor
         ├── Printer
         └── Speakers

Remember:

IPO:
Input → Process → Output

CPU:
ALU + CU + Registers

Instruction Cycle:
Fetch → Decode → Execute → Store

Three Main Buses:
Data → Address → Control

Key Takeaways

• A computer accepts input, processes it and produces output.

• Computers are fast, accurate, diligent, versatile and capable of storing large amounts of data.

• The CPU is responsible for processing and controlling operations.

• ALU performs arithmetic and logical operations.

• CU controls and coordinates computer operations.

• Registers provide very fast temporary storage.

• RAM is volatile memory.

• ROM is non-volatile memory.

• Input devices provide data to the computer.

• Output devices present processed information.

• The Fetch–Decode–Execute cycle is fundamental to instruction processing.

• Data becomes useful information after processing.