Why do computers only use 0 and 1? Why not 0 to 9 like us?
Yash Tiwari11th Sample
6 Oct 2026 · 1 min read
bhai ek bahut basic doubt hai, shayad stupid lage but pooch raha hu. I'm PCB, class 11, and our computer teacher said "computers only understand 0 and 1". Okay but WHY? Humans use 0 to 9, so why not make computers with 10 digits? Seems like making life harder for the computer.
What I tried: googled it and found "transistors are switches, on and off". Fine, that explains two states, but why can't a switch have 3 or 10 positions? A fan regulator has 1, 2, 3, 4, 5 and it works. So why not that?
Also I tried to convert something myself. 1010 in binary: 1×8 + 0×4 + 1×2 + 0×1 = 10? Is that right?
And how does a computer store the letter "A" or a photo if it only has 0s and 1s? I know it's a basic thing but it's been bugging me since morning.
One more. My friend (PCM, so I trust him but only like 80%) says "1 byte can store 256", so does that mean the biggest number in one byte is 256?
Please explain simple, Hinglish is fine. I promise I'll not ask "why is the sky blue" next.
12 answers & replies
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[+][–]Kabir Joshi11thSample· 13d ago
the reason is noise. A transistor outputs a voltage. With two states you only need to decide "is this voltage high or low". There is a big gap in between, so even if there's electrical noise the circuit still gets it right. Now imagine 10 states: the voltage levels would be very close together, like 0.1V, 0.2V, 0.3V. A small disturbance and 3 becomes 4. Two levels = very reliable and cheap to build. That's the main reason
[+][–]Yash Tiwari11thSample· 13d agoAuthor
ok but the fan regulator has 5 steps and works fine no?
[+][–]Tushar PawarDropperSample· 13d ago
The regulator works because it's one switch in your hand and you can see the result. Now imagine millions of them chained together, and each one copies a signal onto the next. Small errors pile up. With on/off, each stage cleans the signal back to a clear high or low. That's why a digital copy of a file is exact, while a photocopy of a photocopy of a photocopy goes grey and blurry. Also fun fact, computers with three states (ternary) have actually been built in the past, so it's possible. Two just won because it's simpler and more reliable.
[+][–]Vivek Mishra12thSample· 13d ago
Your 1010 is right. It is 10. The place values go 8, 4, 2, 1 from the left, like units, tens, hundreds in our normal numbers but doubling each time. So 1010 = 8 + 2 = 10. Try one more: 45 = 32 + 8 + 4 + 1, so 101101. Check: 32+0+8+4+0+1 = 45.
[+][–]Dev Agarwal12thSample· 13d ago
1 byte = 8 bits, 2^8 = 256, so the max number is 256. Your friend is correct and the max is 256
[+][–]Neel Chatterjee12thSample· 13d ago
Small correction. 256 is the number of different values one byte can hold, but they start from 0, so the biggest value is 255. Eight ones in a row, 11111111, is 128+64+32+16+8+4+2+1 = 255. Same as how two decimal digits give 100 different values, 00 to 99, but the biggest is 99, not 100.
[+][–]Dev Agarwal12thSample· 13d ago
yep, off by one, my bad. the classic
[+][–]Meera Patel11thSample· 13d ago
For letters and photos: everything is encoded by agreement. For letters, people agreed on a table, so the number 65 means "A", 66 means "B", and so on. 65 in binary is 01000001. For a photo, the screen is a grid of tiny dots (pixels), and each pixel stores how much red, green and blue it has, each a number from 0 to 255 (one byte each). A 1920 × 1080 photo has 2,073,600 pixels, so you can see why photos need so much storage.
[+][–]Ananya Reddy11thSample· 12d ago
follow up from a fellow PCB person. How does the computer know that 01000001 is the letter A and not the number 65?
[+][–]Kabir Joshi11thSample· 12d ago
it doesn't know by itself. The same bits can be read in different ways. The program tells it how to interpret them. If a text editor reads that byte, it shows A. If a calculator program reads it, it shows 65. You can try in Python:
chr(65)gives 'A' andbin(65)gives '0b1000001'. Same thing, two views.
[+][–]Harsh Gupta12thSample· 12d ago
the real answer is that computers are just very fast and very dumb, which is also why they're good at exams
[+][–]Yash Tiwari11thSample· 12d agoAuthor
okay this was a banger thread. noise = reason for 2 levels, 255 not 256, same bits can mean A or 65. Thanks everyone, ab pata chala why my computer sir said what he said. next doubt: why does 0.1 + 0.2 not equal 0.3 in Python (I saw a meme)
