What Is a Computer? The Machine That Only Follows Instructions
A computer is fast, not clever. It follows the steps you give it, millions of times every second, and it understands not one of them.
The whole idea, in one diagram
You put something IN: a tap, a word, a photo, a number.
The computer WORKS on it by following instructions somebody wrote.
It sends something OUT: a picture on a screen, a sound, a printed page.
What problem did it solve?
Sums had to be done by hand. Working out the tides, or the path of a planet, or the wages for a whole factory could take a team of people weeks, and one tired mistake ruined the whole answer.
People built a machine that could carry out a list of instructions on numbers, over and over, without getting bored, hungry or careless.
Work that took weeks now takes a blink. That one change sits underneath hospitals, aeroplanes, schools, banks, phones and every game you have ever played.
How it started
- about 2500 BC
The abacus
👤 Traders in Mesopotamia, later China and the Middle East
Beads on rods stood for ones, tens and hundreds. Slide the beads, and you have added up.
Why it mattered: It was the first time counting was moved OUT of a person's head and into an object. Every computer since has done the same thing, just faster.
- about 820
Al-Khwarizmi writes down step-by-step methods
👤 Muhammad ibn Musa al-Khwarizmi, Baghdad
He wrote books explaining how to solve problems by following an exact list of steps in order.
Why it mattered: The word algorithm comes from his name. An algorithm is simply a recipe, and a recipe is the only thing a computer can actually follow.
- 1837
The Analytical Engine is designed
👤 Charles Babbage, England
Babbage designed a giant machine of brass gears that could store numbers, do sums and follow instructions punched into cards. He never finished building it.
Why it mattered: It was the first design for a machine that could be given a NEW job without being rebuilt. That is the whole idea of a computer.
- 1843
The first computer program is written
👤 Ada Lovelace, England
Ada wrote out a full set of steps for Babbage's machine to calculate a sequence of numbers, and added notes saying the machine could one day work on music and pictures too, not only sums.
Why it mattered: She is called the world's first programmer. She also spotted, a hundred years early, that a computer works on anything you can turn into numbers.
- 1946
ENIAC switches on
👤 A team in Pennsylvania, USA. Six women wrote its programs.
ENIAC filled a whole room, weighed about 30 tonnes and used 18,000 glass valves. It was programmed by moving cables and flicking switches by hand.
Why it mattered: It proved an electronic computer could work at speed. It also showed the problem: it was enormous, hot and needed a crew to run it.
- 1947
The transistor is invented
👤 John Bardeen, Walter Brattain and William Shockley at Bell Labs, USA
A tiny switch made of a special material replaced the big, hot, fragile glass valve.
Why it mattered: This is the single reason computers got small. Everything after this, from laptops to phones, is really the story of the transistor shrinking.
- 1971
A whole processor on one chip
👤 Intel, USA
The Intel 4004 packed thousands of transistors onto a fingernail-sized chip. A room of machinery became a component you could hold.
Why it mattered: Once the brain was a cheap little chip, a computer could be put inside anything: a watch, a car, a microwave, a toy.
- 1977 to 1981
Computers arrive in ordinary homes
👤 Apple, Commodore, IBM and others
The Apple II, then the IBM PC, were sold to families and small businesses rather than to universities and armies.
Why it mattered: For the first time a computer was something a child could switch on at home. That is the moment computing stopped being a job and became normal life.
Who made it happen
Al-Khwarizmi
about 780 to 850 · Baghdad
Wrote down how to solve problems as an exact list of steps. The word algorithm is made from his name.
Charles Babbage
1791 to 1871 · England
Designed the Analytical Engine, the first machine meant to follow instructions instead of doing one fixed job.
Ada Lovelace
1815 to 1852 · England
Wrote the first computer program, and was the first person to realise a computer could work on more than numbers.
Alan Turing
1912 to 1954 · England
Worked out what any computer can and cannot do, and helped break secret wartime codes with machines.
Grace Hopper
1906 to 1992 · USA
Built the first tool that turned words a human could read into instructions a machine could run.
The ENIAC six
1946 · USA
Six women, including Jean Bartik and Betty Holberton, programmed the first big electronic computer by hand.
How your tap turns into an answer
- 1
You put something in
You tap a key, touch the screen, speak, or take a photo. This is called input. The computer turns all of it into numbers, because numbers are the only thing it can hold.
- 2
Memory holds it still
The numbers are parked in memory, a bit like a huge wall of numbered lockers. Every locker has an address so the computer can find it again instantly.
- 3
The processor reads the instructions
A program is a list of very small instructions: fetch this number, add that one, compare them, jump back. The processor reads one, does it, and moves to the next.
- 4
It repeats, unbelievably fast
Each single step is tiny and rather boring. The trick is speed. A normal phone chip does billions of these steps every second, which is why it feels instant.
- 5
It sends something out
The finished numbers become something you can sense: pixels on a screen, sound from a speaker, ink on paper. This is called output.
Each invention solved the last one's problem
Room-sized computer
- Problem before
- Only an army, a government or a university could afford one, and it needed a team of trained people just to switch it on.
- What it solved
- It could finally do enormous calculations in hours instead of months.
- Impact
- Weather forecasts, space flight and code breaking all became possible. Ordinary people never touched one.
Personal computer
- Problem before
- A machine that fills a room cannot sit on a desk, and nobody wanted to book a slot to write a letter.
- What it solved
- The transistor and the chip shrank the whole machine to the size of a typewriter, at a price a family could just about reach.
- Impact
- Homes, schools and small shops got computers. Writing, drawing, accounts and games moved onto screens.
Laptop
- Problem before
- A desktop still lived on one desk, in one room, plugged into one wall.
- What it solved
- Screen, keyboard, brain and battery were folded into a single box you could carry.
- Impact
- Work and school stopped needing a fixed place. You will meet this story properly in Part 2.
Watch it happen, step by step
Tap through the animation. You can switch it to Urdu with the button.
How does a computer add 2 + 3?
A computer is fast, not clever. It does exactly what its instructions say, so if something goes wrong, a human wrote the wrong instruction.
Walk around your home and count the computers. Do not stop at the obvious ones. There is a small computer inside a microwave, a washing machine, a TV remote, a car, a smart watch and most modern toys. Most people guess three and find more than twenty.
Key words on this page
- What is a Computer?کمپیوٹر کیا ہے؟
- A computer is a machine that follows instructions to do jobs for us. It can draw pictures, play music, show videos, and help us learn. Computers work very, very fast!
- Did you know? The first computers were as big as an entire room!
- Hardwareہارڈویئر
- Hardware is every part of a computer that you can touch and hold. The screen, the keyboard, and the mouse are all hardware. If you can pick it up, it is hardware!
- Did you know? A computer can have hundreds of tiny hardware parts inside it!
- Softwareسافٹ ویئر
- Software is the set of instructions that tells the computer what to do. You cannot touch software, it lives inside the computer. Games, drawing apps, and video players are all software.
- Did you know? One smartphone app can have millions of instructions inside it!
- The Mouseماؤس
- A computer mouse is a small device you move with your hand to point at things on the screen. When you click its buttons, you can open apps and choose things. It was called a mouse because its wire looked like a little tail!
- Did you know? The very first mouse was made of wood in 1964!
- Screen and Keyboardاسکرین اور کی بورڈ
- The keyboard is how you type letters and numbers into the computer, it is an input device. The screen shows you what the computer is doing, it is an output device. Input means putting things in; output means getting things out!
- Did you know? A standard keyboard has 104 keys, that is a lot of buttons!
- The CPU — The Brainسی پی یو — دماغ
- The CPU stands for Central Processing Unit and it is the brain of the computer. It reads instructions and carries them out billions of times every second. Without the CPU, the computer cannot do anything at all.
- Did you know? A modern CPU can carry out more than 3 billion instructions every single second!
- Memory vs Storageمیموری بمقابلہ اسٹوریج
- Memory (called RAM) is like your desk, it holds the things you are using right now, but when you turn off the computer it all goes away. Storage (like a hard drive) is like your backpack, things stay there even when the computer is switched off.
- Did you know? When you save a file, you are moving it from your desk (memory) to your backpack (storage)!
- The Operating Systemآپریٹنگ سسٹم
- An operating system is the boss program that runs everything on a computer. It looks after the screen, keyboard, and all the apps. Windows on a PC, Android on most phones, and iOS on iPhones are all operating systems.
- Did you know? Without an operating system, your computer screen would just stay dark and nothing would work!
- Apps and Programsایپس اور پروگرام
- An app, short for application, is a piece of software made to do one job really well. There are apps for games, drawing, maths, watching videos, and even learning! Apps are the programs you open and use every day.
- Did you know? There are more than 3 million different apps available to download today!
- Phones and Tablets are Computers Too!فون اور ٹیبلیٹ بھی کمپیوٹر ہیں!
- Yes! A smartphone or tablet has a CPU, memory, storage, and an operating system, just like a laptop or desktop computer. The big difference is that it fits in your hand and can make calls. Phones are actually tiny, very powerful computers!
- Did you know? Your smartphone is more powerful than the computers that sent astronauts to the moon in 1969!
- Binary — 0s and 1sبائنری — صفر اور ایک
- Computers are made of millions of tiny switches that are either OFF (0) or ON (1). By combining billions of these 0s and 1s in different patterns, a computer can represent every letter, picture, and sound in the world. This secret language is called binary.
- Did you know? The letter 'A' in binary is written as 01000001, eight tiny switches!
- What is Code?کوڈ کیا ہے؟
- Code is a set of instructions that humans write for computers using special languages like Python, JavaScript, or Scratch. Just like a recipe tells you how to bake a cake, code tells a computer exactly what to do, step by step. People who write code are called programmers.
- Did you know? Ada Lovelace wrote the world's very first program ideas in the 1840s, long before computers were even built!
- What is the Cloud?کلاؤڈ کیا ہے؟
- Your photos are not floating in the sky! They are saved on huge, powerful computers called servers in big buildings around the world. These servers are connected to the internet, so you can reach your photos from any device, anywhere. This network of remote computers is called the cloud.
- Did you know? The world's cloud data centres use as much electricity as some entire countries!
- From Room-Size to Your Pocketکمرے کے سائز سے جیب تک
- Early computers used huge glass tubes to work, which needed a lot of space and power. In 1947 scientists invented the transistor, a tiny switch, which replaced those tubes. Then engineers packed millions of transistors onto a single tiny chip called a microprocessor, and computers shrank from room-sized to pocket-sized.
- Did you know? A modern chip smaller than your fingernail can hold more than 50 billion transistors!
- What is a Server?سرور کیا ہے؟
- A server is a powerful computer that stores information and sends it to other computers when they ask for it. When you open a website, a server somewhere in the world receives your request and sends back the web page. Servers work non-stop, day and night, to serve millions of people at once.
- Did you know? Google has more than a million servers around the world working together to answer your searches in less than a second!
Quiz: how much did you remember?
Quiz time!
10 questions, picked at random from 30. No sign-in and no score is kept. Play as many times as you like, the questions change every time.
Questions about computers
What is a computer in simple words?
A computer is a machine that takes in information, follows a list of instructions to work on it, and gives you a result. That is really all it does. It just does it very, very fast.
Who invented the computer?
No single person did. Charles Babbage designed the first proper computer in 1837, Ada Lovelace wrote the first program for it in 1843, and a team in America built ENIAC, the first big electronic one, in 1946. Each of them added a piece.
Is a computer clever?
No. A computer has no idea what it is doing. It follows instructions without understanding them, a bit like someone who can read a recipe in a language they do not speak. Everything smart about a computer was put there by a person.
What are the main parts of a computer?
Input parts such as a keyboard, mouse, touchscreen or camera. A processor, which does the work. Memory and storage, which hold information. Output parts such as a screen, a speaker or a printer.
What is the difference between memory and storage?
Memory is the desk you are working at right now. It is fast, and it is emptied when the power goes off. Storage is the cupboard. It is slower, but it keeps your files when the computer is switched off.
Why do computers only understand 0 and 1?
Inside a chip there are billions of tiny switches, and a switch can only be off or on. We write off as 0 and on as 1. Every word, photo, song and game is built out of huge patterns of those two.
Is a mobile phone a computer?
Yes. A modern phone is a full computer with a screen, a processor, memory, storage and a battery. It is far more powerful than the machines that first sent people to the Moon.
How fast is a computer really?
A normal phone or laptop chip carries out several billion tiny steps every second. In the time it takes you to blink, it has done more separate steps than there are people alive on Earth.
Want lessons that are marked and saved?
The free courses run from playgroup to Grade 5, in order, with three difficulty levels.
See the free courses →