GCSE · Computer Science · AQA · Spec 8525

Terabyte (TB)

A terabyte is a million million bytes: 1,000,000,000,000. You can't picture that, and you don't need to. You just climb four steps, each exactly the same size.

The byte ladder

Tap each unit, left to right. Every step along this axis is the same jump: ×1,000.

Byte (B)

1 byte

The bottom rung: one byte. Every unit to the right is just a bigger count of bytes.

Estimate first

How many megabytes fit in one terabyte?

Slide to your best guess, then lock it in: how many megabytes (MB) are in 1 terabyte (TB)?

Your estimate

750000 megabytes

Slide to your best guess, then lock it in: how many megabytes (MB) are in 1 terabyte (TB)? Estimate between 0 megabytes and 1500000 megabytes.

0 megabytes1500000 megabytes

What do you think?

1 TB is how many GB?

Two friends are arguing. One says a terabyte is 1,000 gigabytes. The other is sure it's 1,024.

Which is closest to what you think right now?

1 TB is 1,000 GB. Tera is one ×1,000 step above giga, like every other rung.1 TB is 1,024 GB, because computers work in binary.1 TB is 1,000,000 GB, because a terabyte is so enormous.

How sure are you?

I'm sureI think soI'm guessing

1 TB is 1,000 GB. Tera is one ×1,000 step above giga, like every other rung.

This matches the evidence

Spot on. Kilo, mega, giga and tera are decimal prefixes. They're SI prefixes, and SI prefixes are based on powers of 10, so every step is exactly ×1,000. One step up from giga is tera: 1 TB = 1,000 GB.

1 TB is 1,024 GB, because computers work in binary.

This is a common misconception

You haven't made 1,024 up. Historically, words like kilobyte and megabyte have often been used for powers of 2, and 1,024 is 2¹⁰, a power of 2 that happens to be close to 1,000. But tera and giga are decimal prefixes, based on powers of 10. Used that way, 1 TB is exactly 1,000 GB, not 1,024.

1 TB is 1,000,000 GB, because a terabyte is so enormous.

This is a common misconception

That's one rung too far. Tera sits just ONE step above giga, so it's ×1,000: 1 TB = 1,000 GB. A million is what you get across TWO steps, which is why 1 TB = 1,000,000 MB.

One rung is ×1,000. Tera is one rung above giga, so 1 TB = 1,000 GB, exactly.

Big B or little b?

Bytes or bits?

Is each amount measured in bytes or in bits? Look closely at the letter b.

Still to sort

Bytes (B) (0)

Capital B. A byte is a group of 8 bits.

Where the line is: Only the case of the letter separates them: B is byte, b is bit.

Bits (b) (0)

Lower-case b. A bit is a single 0 or 1.

Where the line is: Only the case of the letter separates them: b is bit, B is byte.

6 of 6 still to sort.

One letter's case changes the unit, and the amount changes by a factor of 8.

Your turn

Take 3 TB all the way down to bits

Convert 3 TB into bytes, and then into bits.

Start with 3 TB. We're heading down to smaller units, so we'll need more of them: multiply.Decide the direction before you touch a number.
missing step

Which line is step 2?

3 TB + 1,000 = 1,003 GB3 TB × 1,000 = 3,000 GB3 TB ÷ 1,000 = 0.003 GB

Compare

Which is the most data?

Order these amounts of data from largest to smallest

1 · Largest5 · Smallest

450 GB
2 TB
600,000 MB
0.5 TB
1,500 GB

Watch out: Don't judge by the digits or by the unit alone. Convert everything to one unit first.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

1 TB is 1,000 GB: the top rung of a ladder where every step is ×1,000.

What you need to know

1 TB (terabyte) = 1,000 GB (gigabytes).
Kilo, mega, giga and tera are decimal prefixes. They're SI prefixes, based on powers of 10, so each step is ×1,000.
1 GB = 1,000 MB, 1 MB = 1,000 kB and 1 kB = 1,000 bytes.
A bit is a single 0 or 1. A byte is a group of 8 bits. B means byte; b means bit.
To compare amounts of data, convert them into the same unit first.

The big picture

Amounts of data are counted in bytes, and prefixes make big counts manageable. Kilo, mega, giga and tera are decimal prefixes: each one is 1,000 times the one before, so 1 kB = 1,000 bytes, 1 MB = 1,000 kB, 1 GB = 1,000 MB and 1 TB = 1,000 GB. Going down to a smaller unit, multiply by 1,000 for every step. Going up, divide. Crossing two steps means ×1,000 twice, which is ×1,000,000. Watch the letter case too: capital B is a byte, lower-case b is a bit, and a byte is a group of 8 bits.

Key points

1The ladder runs byte, kB, MB, GB, TB, and each rung is 1,000 times the one below.

2Going down to a smaller unit, multiply by 1,000 per step. Going up to a bigger unit, divide by 1,000 per step.

3Crossing two rungs is ×1,000 × 1,000 = ×1,000,000, so 1 TB = 1,000,000 MB.

41 TB is a million million bytes (10¹²): four ×1,000 steps above one byte.

5Bytes to bits is ×8, not ×1,000.

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Worked example

Problem

A folder of photos takes up 45,000 MB. How big is that in terabytes?

⚠ Watch out

Going the wrong way. When you convert to a SMALLER unit (TB to GB), you need MORE of them, so multiply. Dividing there gives an answer that's a million times too small.

🧠

Memory hook

Kind Monkeys Grow Tall: kilo, mega, giga, tera. Every monkey is 1,000 times taller than the one before.

✓

Check yourself

Without looking back: why is 1 TB 1,000 GB and not 1,024 GB? Then turn 4 TB into GB, and then into MB.

Flashcards

(13)

1 TB = how many GB?

1,000 GB

1 GB = how many MB?

1,000 MB

What does kilo mean in 1 kB?

1,000, so 1 kB = 1,000 bytes.

1 MB = how many kB?

1,000 kB, which is a million bytes.

Order from smallest to largest: GB, kB, TB, MB

kB, MB, GB, TB

What kind of prefixes are kilo, mega, giga and tera?

Decimal prefixes: SI prefixes based on powers of 10.

What is a bit?

The fundamental unit of information: a single 0 or 1.

What is a byte?

A group of 8 bits.

B or b: which one means bit?

Lower-case b is bit. Capital B is byte.

How many megabytes are in one terabyte?

1,000,000 MB: two ×1,000 steps.

How many bytes are in one terabyte?

A million million (10¹²): four ×1,000 steps above one byte.

Why does 1,024 sometimes turn up for kilobyte, megabyte and so on?

Historically these terms were often used for powers of 2 (1,024 = 2¹⁰). As decimal prefixes they mean powers of 10.

Converting TB to GB: multiply or divide?

Multiply by 1,000. A smaller unit means more of them.

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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How many megabytes fit in one terabyte?

1 TB is how many GB?

Bytes or bits?

Take 3 TB all the way down to bits

Which is the most data?

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