Definition
A bit (short for binary digit) is the most fundamental unit of information in computing. It can hold exactly one of two values: 0 or 1.
These two values correspond to the two states of an electronic switch inside a computer: off (0) and on (1). Because all computer hardware is built from billions of such switches (transistors), all data — text, images, video, programs — is ultimately stored and processed as sequences of 0s and 1s.
The Bit as an On/Off Switch
Think of a bit like a single light switch. It is either:
- Off → represented as
0 - On → represented as
1
A single switch carries very little information, but combine millions of switches and you can represent anything.
One bit can distinguish between exactly 2 different states. Two bits can represent 4 states (00, 01, 10, 11). Three bits give 8 states. In general, n bits can represent 2 to the power of n different values.
From Bits to Bytes
Because a single bit can only hold 0 or 1, bits are almost always grouped together to store meaningful data.
| Unit | Composition | Distinct values |
|---|---|---|
| Bit | 1 bit | 2 |
| Nibble | 4 bits | 16 |
| Byte | 8 bits | 256 |
A byte (8 bits) is the standard building block for all storage measurements. With one byte you can represent 256 different values (0 to 255), which is enough to encode every letter, digit, and common punctuation character in the ASCII standard.
For example, the letter A is stored as 01000001 (decimal 65).
Storage Units
Storage capacity is measured in multiples of bytes:
| Unit | Approximate size | Example use |
|---|---|---|
| Kilobyte (KB) | 1 024 bytes | A short text email |
| Megabyte (MB) | 1 024 KB | A medium photo |
| Gigabyte (GB) | 1 024 MB | A HD film |
| Terabyte (TB) | 1 024 GB | A large hard drive |
Be careful not to confuse bits and bytes. Internet speeds are measured in bits per second (Mbps), while file sizes are measured in bytes (MB, GB). A 100 Mbps connection transfers 100 megabits — only 12.5 megabytes — per second.
Why Bits Are Fundamental
Every operation a computer performs — arithmetic, comparing text, drawing a pixel, playing audio — ultimately comes down to manipulating bits. Understanding bits helps you make sense of:
- Why file sizes are what they are.
- How colours are encoded (e.g. 24-bit colour = 3 bytes per pixel).
- Why passwords and encryption keys are described in bits (e.g. "256-bit encryption").
Practice Problems
How many different values can 3 bits represent?
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How many bits are in one byte?
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A file is 2 MB. Approximately how many bytes is that?