GCSE · Computer Science · AQA · Spec 8525

Bits and bytes

Every message, photo and song on your phone is built from one tiny thing that can only say 0 or 1.

Try it

Flip a switch. Then count to eight.

8-bit binary 01101001 = 105 in denary. All eight together: 1 byte

All eight together1 byte

Tap any box. Can you make a 2?

Each box is one bit. Tap it and it flips: 0 becomes 1, 1 becomes 0. You can't make a 2, because there is no third setting. A bit can only ever be 0 or 1, and 0 is a real value, not an empty box. Now count the boxes. Eight bits side by side make one byte. (The small numbers above the boxes are for turning a byte into a number. That's a different lesson, so today just count the boxes.)

Predict, then check

The number is the same. Only one letter is different.

Which is more data: 16 b or 16 B?

What do you really think?

Four ideas about bits and bytes

Four students are revising together, and each one says what they think bits and bytes are.

Which one is closest to what you think right now?

A bit is one digit, so it can be anything from 0 to 9.A byte is 10 bits. Computers like nice round numbers.A bit is made of bytes, like a word is made of letters.A bit is just a 0 or a 1, and a byte is 8 bits grouped together.

How sure are you?

I'm sureI think soI'm guessing

A bit is one digit, so it can be anything from 0 to 9.

This is a common misconception

That's how digits work when we count in everyday life, but a bit isn't an everyday digit. It has exactly two possible values: 0 or 1. Think back to the boxes you tapped at the top. However many times you pressed one, it only ever flipped between 0 and 1.

A byte is 10 bits. Computers like nice round numbers.

This is a common misconception

Ten feels right because we count in tens. But a byte is a group of exactly 8 bits. Count the boxes in the row you played with: eight, not ten.

A bit is made of bytes, like a word is made of letters.

This is a common misconception

It's the other way round. The bit is the smallest piece of information there is. Bytes are made out of bits: put eight bits together and you have one byte. So the byte is the word, and the bits are its letters.

A bit is just a 0 or a 1, and a byte is 8 bits grouped together.

This matches the evidence

Spot on. A bit is the fundamental unit of information, the smallest piece there is, and it can only be 0 or 1. Group eight bits together and you have a byte.

Bits are the smallest pieces, and each one is only ever 0 or 1. Bytes are built from bits, exactly 8 bits to every byte.

Your turn to write

Say it in your own words

State what is meant by a bit and what is meant by a byte. [3 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

A bit is the fundamental unit of information (accept: the smallest unit of information or data) (1 mark)
A bit is either 0 or 1 (accept: has only two values, 0 and 1) (1 mark)
A byte is a group of 8 bits (1 mark)

Model answer

A bit is the fundamental unit of information. It can only have the value 0 or 1. A byte is a group of 8 bits.

Three separate facts, three separate marks: the smallest unit, only 0 or 1, and 8 bits to a byte. Leave one out and that mark goes with it.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

One tiny switch. Then eight of them in a row.

What you need to know

A bit is the fundamental unit of information.
A bit is either 0 or 1.
A byte is a group of 8 bits.
b stands for bit and B stands for byte.

The big picture

A bit is the fundamental unit of information: the smallest piece of data there is. Each bit is either 0 or 1, and nothing else. Group 8 bits together and you have a byte. In symbols, lowercase b stands for bit and uppercase B stands for byte, so 1 B is the same amount as 8 b.

Key points

1Everything a computer stores is built from bits.

2A byte is exactly 8 bits, not 10.

3Bytes to bits: multiply by 8. Bits to bytes: divide by 8.

4Same number, different letter: 10 B is eight times as much as 10 b.

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Worked example

Problem

A short text message is stored in 5 B. How many bits is that?

⚠ Watch out

Mixing up b and B. 8 b is one byte, but 8 B is 64 bits, which is eight times as much.

🧠

Memory hook

Bit is short for binary digit, and binary only has two digits, 0 and 1. For the symbols: Big B, Bigger amount. The capital B is the byte, eight times the size of a bit.

✓

Check yourself

A file is 64 b. How many bytes is that? (Answer: 8 B, because every byte is 8 bits and 64 ÷ 8 = 8.)

Flashcards

(6)

What is a bit?

The fundamental unit of information: the smallest piece of data there is.

What values can a bit have?

Only 0 or 1.

What is a byte?

A group of 8 bits.

What do the symbols b and B stand for?

b stands for bit. B stands for byte.

Which is bigger: 1 b or 1 B?

1 B. A byte is 8 bits, so it is eight times as much as 1 b.

Converting between bytes and bits: when do you multiply by 8, and when do you divide?

Going from bytes to bits, multiply by 8 (each byte holds 8 bits). Going from bits to bytes, divide by 8 (it takes 8 bits to fill a byte).

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Flip a switch. Then count to eight.

Four ideas about bits and bytes

Say it in your own words

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