The Smallest Unit: The Bit
Every piece of information inside a computer is stored as a series of tiny electrical signals that are either on or off. We represent these as 1 (on) and 0 (off). Each single 1 or 0 is called a bit, which is short for binary digit.
A single bit can only store two possible values: 0 or 1. That might not sound very useful, but when you combine many bits together, you can represent enormous amounts of information.
Grouping Bits into Bytes
Eight bits grouped together make one byte. A byte can represent 2⁸ = 256 different values (0 through 255).
Here is why grouping matters. One byte is enough to store:
- A single character of text (like the letter A)
- A number between 0 and 255
- One colour channel in a pixel
Half a byte (4 bits) is called a nibble. It can hold 16 different values and corresponds to a single hexadecimal digit.
Larger Units of Data
As files and storage devices got bigger, we needed larger units. Here is how they scale up:
| Unit | Symbol | Approximate Size |
|---|---|---|
| Bit | b | Single 0 or 1 |
| Byte | B | 8 bits |
| Kilobyte | KB | 1,000 bytes (or 1,024 bytes*) |
| Megabyte | MB | 1,000 KB |
| Gigabyte | GB | 1,000 MB |
| Terabyte | TB | 1,000 GB |
*There are two conventions: the SI standard uses 1 KB = 1,000 bytes, while many operating systems use 1 KB = 1,024 bytes (called a kibibyte, KiB). This is why your 500 GB hard drive looks smaller when plugged into your computer!
A typical music track is about 4–5 MB. A high-quality photo is around 3–8 MB. A full HD movie can be 4–15 GB. Knowing these rough sizes helps you estimate how much storage you need.
How Many Values Can N Bits Store?
The formula is simple: 2ⁿ values, where n is the number of bits.
- 1 bit → 2 values (0 or 1)
- 2 bits → 4 values (00, 01, 10, 11)
- 8 bits → 256 values
- 16 bits → 65,536 values
- 32 bits → over 4 billion values
This is why older computers could only handle smaller numbers and addresses — they had fewer bits to work with.
Bits vs Bytes in Internet Speeds
Internet speeds are measured in bits per second (bps), not bytes. So a "100 Mbps" broadband connection transfers 100 megabits — only 12.5 megabytes — per second. This is why downloading a 50 MB file on a 100 Mbps connection takes a few seconds, not an instant.
Practice Problems
How many different values can be stored in 4 bits? List all of them in binary.
Show answer
A file is 2.5 MB in size. How many kilobytes is that? If you are downloading it on a 10 Mbps connection, roughly how long will it take?