Introduction to Computers

Introduction to Computers — AKUEB Computer Studies (SSC)

1. What is a Computer?

A computer is a programmable electronic device that accepts data as input, processes it according to a set of instructions (a program), and produces information as output. The results can be stored for later use.

Key distinction: Data vs. Information

• Data = raw, unprocessed facts and figures. Example: 42, "Ahmed", 37.5°C
• Information = data that has been processed to give it meaning. Example: "Ahmed's temperature is 37.5°C — within the normal range."

2. Classification of Computers

Computers are classified by size, power, and purpose:

3. Components of a Computer System

A computer system has three main categories of components:

Hardware: Physical components you can touch.

Input devices: Allow data to enter the computer

• Keyboard, mouse, scanner, microphone, touchscreen, barcode reader, webcam

Output devices: Present processed information to the user

• Monitor (screen), printer, speakers, projector

Storage devices:

• Primary storage (RAM): Temporary, fast, volatile (data lost when power off) — stores running programs
• Primary storage (ROM): Permanent, non-volatile — stores boot instructions (BIOS/UEFI)
• Secondary storage: Permanent — hard disk drive (HDD), solid-state drive (SSD), USB flash drive, optical disc (CD/DVD)

Processing unit:

• CPU (Central Processing Unit): The "brain" of the computer — executes all instructions
• Control Unit (CU): Fetches and decodes instructions
• Arithmetic Logic Unit (ALU): Performs calculations and logical comparisons
• Cache memory: Very fast, small memory inside the CPU for frequently used data

4. Software

Software is the set of instructions that tells hardware what to do. It has no physical form.

System software:

• Operating System (OS): Manages hardware resources, provides user interface, runs other programs. Examples: Windows 11, Android, Linux
• Utility software: Performs maintenance tasks. Examples: antivirus, disk defragmenter, file compression

Application software:

• Programs designed for specific user tasks
• Examples: Microsoft Word (word processing), Chrome (web browser), VLC (media player), Kahoot (education), WhatsApp (communication)

5. How a Computer Processes Data: The IPO Cycle

Every computer operation follows the Input → Process → Output (IPO) model:

1. Input: Data enters the computer (keyboard press, mouse click, sensor reading)
2. Process: The CPU follows program instructions to transform the data
3. Output: The result is displayed, printed, or stored
4. (Storage): Processed data may be saved for future use

Pakistan example: When you use Easypaisa on your phone to send money:

• Input: You enter the recipient's number and amount
• Process: The app verifies your account and calculates the transfer
• Output: A confirmation message and transaction receipt

6. Binary and Data Representation

Computers store and process all data as binary (base-2) — combinations of 0s and 1s, because electronic circuits can only be in two states: OFF (0) or ON (1).

• A single binary digit is called a bit
• 8 bits = 1 byte
• 1024 bytes = 1 kilobyte (KB)
• 1024 KB = 1 megabyte (MB)
• 1024 MB = 1 gigabyte (GB)

All data — text, images, sound, video — is ultimately stored as binary numbers inside the computer.