# Bits, bytes and binary Computers only “see” two signals: **0** and **1**. That system is **binary**. - 1 **bit** = one 0 or 1 - 8 bits = 1 **byte** - 1024 bytes ≈ 1 **KB** - 1024 KB ≈ 1 **MB** - 1024 MB ≈ 1 **GB** ## Why two symbols? Electric switches are easy: on / off. Billions of switches make photos, songs, and games. ## Text The letter A can be stored as the number 65, which the computer stores in bits. > You do not need to count bits every day — but now you know why a 10-minute video is a large file: many 0s and 1s. ## You do not need to be a bit-counter You need three facts: 1. Underneath, it is 0 and 1 2. 8 bits make a byte — the usual “one character” sized brick 3. File size is just “how many of those bricks” A 10-minute HD video is large because it is millions of coloured dots, many times a second, each stored as bits. ### Rough everyday sizes (order of magnitude) | Thing | Rough size | | --- | --- | | A short text message | bytes to a few KB | | A school essay | tens of KB | | A phone photo | 1–5 MB | | A song | 3–8 MB | | A short HD video | tens to hundreds of MB | | A movie | 1–4 GB | If a “photo” you download is 800 MB, it is probably a trick or a video labelled wrong — ask before you open it.