SSC CGL Preparation – Day 2 – Page 9

Table of Contents

🔍 Computer Basics – Introduction to CPU

The Central Processing Unit (CPU) is often referred to as the brain of the computer. It is responsible for executing instructions, processing data, and controlling the operation of other components in a computer system.

Every task you perform on a computer — from opening a file to playing a game — involves the CPU.

🧩 Components of CPU

The CPU is mainly divided into three parts:

1. Arithmetic Logic Unit (ALU)

Performs arithmetic operations like addition, subtraction, multiplication, and division.
Handles logical operations like comparing numbers (e.g., greater than, less than, equal to).
Works based on instructions received from the Control Unit.

📌 Example: If you perform 3 + 4 in a calculator app, the ALU processes this addition.

2. Control Unit (CU)

Acts as the manager of the CPU.
Directs the flow of data between the CPU and other parts of the computer.
Fetches, decodes, and executes instructions.
Controls input and output operations.

📌 Example: If you click “Save” in MS Word, the CU sends commands to save data in memory or disk.

3. Registers

Small, high-speed storage locations within the CPU.
Temporarily hold data, instructions, and addresses during processing.
Faster than RAM and crucial for CPU speed.

🧠 Types of Registers:

Accumulator – Stores intermediate results
Program Counter (PC) – Holds address of the next instruction
Instruction Register (IR) – Stores current instruction being executed
Memory Address Register (MAR) – Stores address in memory to access
Memory Data Register (MDR) – Stores data to be written/read to/from memory

💻 Working of CPU (Step-by-Step)

The CPU follows a cycle called the Fetch-Decode-Execute Cycle:

Fetch:
- The Control Unit gets the instruction from memory.
Decode:
- The instruction is interpreted (decoded) to understand what action is needed.
Execute:
- The required task (like calculation, memory access) is performed via ALU or CU.

🔁 This cycle repeats millions of times per second.

📦 CPU vs Microprocessor

CPU	Microprocessor
Core unit of a computer	A single chip that acts as a CPU
Can be composed of multiple chips	Single integrated circuit (IC)
Found in desktops and servers	Found in PCs, laptops, embedded devices

🔢 Clock Speed of CPU

Measured in Hertz (Hz).
Common terms:
- MHz (Megahertz) = 1 million cycles/second
- GHz (Gigahertz) = 1 billion cycles/second

🧠 Faster clock speed → faster processing

🧮 Multi-Core Processors

A multi-core processor has more than one CPU core on a single chip.
Each core can execute tasks independently or together, boosting performance.
Common types: Dual-Core, Quad-Core, Octa-Core

📌 Advantage: Efficient multitasking, faster performance in apps like video editing, gaming, etc.

🖥️ CPU Socket and Installation

CPUs are installed on the motherboard using a CPU socket.
It must be compatible with the CPU architecture (e.g., Intel LGA, AMD AM4).
A cooling system (like fan or heat sink) is necessary to prevent overheating.

📚 Summary Table

Term	Function
ALU	Performs arithmetic and logical operations
Control Unit	Directs operations and controls execution of instructions
Registers	Small, fast memory locations for processing
Clock Speed	Determines how many instructions CPU can execute per second
Multi-core	Multiple processing cores in a single CPU for faster performance

📘 Real-Life Analogy

Imagine a CPU as a manager of a factory:

The Control Unit is the supervisor who decides what task to do and in what order.
The ALU is the worker who performs calculations.
The Registers are like desk drawers where small, important notes are kept temporarily.

🔚 Conclusion

The CPU is the powerhouse that drives the entire computer system. Understanding how it works gives you insight into the core mechanics of computing, which is essential for all computer-based competitive exams.

SSC CGL Preparation – Day 2