Computer System: Parts & Evolution
What is a computer system?
A computer is an electronic machine that accepts data, processes it according to a list of instructions (a program) and gives a result. It can also store data and results for later. When we talk about a computer system we mean all the parts working together: the physical machine (hardware), the programs (software), the data and the person using it.
Think of a school canteen. The order slip is the input, the cook is the processor, the recipe book is the program, the store room is memory, and the plate of food you receive is the output. A computer works in exactly this way, only billions of times faster.
Input → Process → Output (IPO cycle)
Every job a computer does follows the same four steps. Remember them as IPOS: Input, Process, Output, Storage.
| Task | Input | Process | Output |
|---|---|---|---|
| ATM withdrawal | Card, PIN, amount | Check PIN and balance, subtract amount | Cash, slip, SMS |
| Google Maps | Destination typed or spoken | Find shortest route using GPS data | Route on screen + voice |
| Online exam | Answers clicked | Compare with answer key, add marks | Score card |
| Selfie with filter | Camera image | Detect face, apply effect | Edited photo |
Main parts of a computer
The diagram below shows how data moves inside a computer. Solid arrows carry data; the Control Unit sends control signals to every part so that they work in the right order.
In the block diagram question, always draw Input → CPU (ALU + CU) ↔ Memory → Output, show secondary storage connected to memory, and label the control signals from the CU.
Input devices
An input device converts what we give (key presses, touch, sound, picture) into binary signals (0s and 1s) that the computer understands.
| Device | What it inputs | Everyday example |
|---|---|---|
| Keyboard | Letters, numbers, commands | Typing a Python program |
| Mouse / touchpad | Pointer movement and clicks | Opening a file |
| Microphone | Sound | "Hey Google, set an alarm" |
| Scanner / camera | Images | Scanning an Aadhaar copy, QR code |
| Biometric sensor | Fingerprint, face | School attendance machine |
| Barcode / QR reader | Printed code | Supermarket billing, UPI payment |
CPU: ALU, CU and registers
The Central Processing Unit (CPU), also called the processor, executes instructions. Today the whole CPU is built on one small chip called a microprocessor.
ALU – Arithmetic Logic Unit
- Does arithmetic: + − × ÷
- Does logic: compare (<, >, ==), AND, OR, NOT
- Example: checks
marks >= 33
CU – Control Unit
- Fetches the next instruction from memory
- Decodes it (understands what to do)
- Sends control signals so the ALU, memory and I/O act in order
Registers are tiny, super-fast storage cells inside the CPU. They hold the instruction being executed, the address of the next instruction and the numbers the ALU is working on. They are faster than cache and RAM, but there are only a few of them.
Output devices
An output device converts binary results back into a form people understand: text, picture, sound or movement.
| Device | Output form | Note |
|---|---|---|
| Monitor (LED/LCD) | Soft copy on screen | Resolution like 1920×1080 pixels |
| Printer | Hard copy on paper | Inkjet, laser; 3D printers make objects |
| Speaker / headphone | Sound | Music, screen reader for visually impaired users |
| Projector | Large picture | Smart class |
| Braille display | Raised dots | Helps blind users read the screen |
Evolution of computers
Computers did not appear suddenly. Each generation became smaller, faster, cheaper and used less power, mostly because the main electronic part changed.
Two big ideas changed everything: John von Neumann's stored-program concept (keep both program and data in memory) and the microprocessor, which put a complete CPU on one chip. Moore's law observed that the number of transistors on a chip roughly doubles every two years.
Hardware vs software
Hardware
- Physical parts you can touch
- Keyboard, CPU chip, RAM, SSD, monitor
- Can break or wear out
- Useless without software
Software
- Set of programs and instructions
- Windows, Python, Chrome, MS Word
- Cannot be touched; can have bugs
- Needs hardware to run
Summary & practice
- Computer = input → process → output + storage, controlled by a program.
- CPU = ALU (calculation and comparison) + CU (control) + registers (tiny fast memory).
- Generations: vacuum tube → transistor → IC → microprocessor → AI.
- Hardware is physical; software is the set of programs that run on it.
1) List the input, process and output when you pay a shopkeeper using a UPI QR code. 2) Which part of the CPU decides that 45 > 33 is true? 3) Name one device that is both input and output.
Answers: 1) Input: QR scan, amount, UPI PIN; Process: bank checks PIN and balance and moves money; Output: "Payment successful" screen and SMS. 2) The ALU. 3) Touch screen.
