Bits and bytes

Summary

A bit holds one of two states, usually written 0 or 1. Eight bits make a byte. A byte has 256 possible patterns, from 00000000 through 11111111. Those patterns do not explain themselves: an agreed rule tells a computer whether a pattern represents a number, text, color, or something else.

Introduction

Electronic circuits can reliably tell two voltage ranges apart. We label those two states 0 and 1. By combining many of these dependable choices, a computer can represent numbers, text, colors, and instructions.

Explanation

With one bit, there are two possible patterns: 0 and 1. Add a second bit and there are four patterns: 00, 01, 10, and 11. Each added bit doubles the number of possible patterns. A byte has eight bits, so it has 256 patterns. The same byte can represent a number, a letter, or part of an image depending on the encoding—the rule used to interpret it.

Real-world example

One byte at a glance

Each of the eight positions can be 0 or 1, so there are 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2, or 256, possible byte patterns. For example, 01000001 can mean decimal 65 when a program expects a number, or the letter A when it expects text. The surrounding format tells the program which meaning to use.

Code example

const letterA = 0b01000001;
console.log(letterA); // 65
// A text encoding can interpret the same value as "A".

Common mistakes

• Calling every group of eight binary digits a visible character.
• Assuming 0 always means false and 1 always means true; their meaning depends on context.
• Forgetting that a byte has 256, not 255, possible patterns because zero is included.

Quiz

Key takeaways

• Bits have two possible states; bytes contain eight bits.
• More bits create exponentially more distinct patterns.
• Encoding rules determine what a bit pattern means.