GCSE · Computer Science · AQA · Spec 8525

Megabyte (MB)

Which is more data: 1,200 kB, or 8,000,000 bits? One number looks enormous. Looks can lie, and soon you'll see exactly how.

Is it more than a megabyte?

Pick an amount, then drop it in a column. Convert it first, then decide. Don't trust how big the number looks.

Still to sort

Less than 1 MB (0)

Converts to fewer than 1,000 kB.

Exactly 1 MB (0)

Converts to 1,000 kB on the dot.

Where the line is: Close isn't good enough. It only belongs here if the conversion lands exactly on 1 MB.

More than 1 MB (0)

Converts to more than 1,000 kB.

7 of 7 still to sort.

1 MB is 1,000 kB, and 1,000 MB is 1 GB. Use that as your yardstick.

Watch out: Check the letter before you touch the number. Capital B is bytes. Small b is bits.

MB or Mb? One letter, eight times the data

Megabyte (MB)vsMegabit (Mb)

Did you notice what happened in the sort? 1,000,000 B and 1,000,000 b look almost identical, but they ended up in different columns. The only difference is the case of one letter.

Focus

The letter

Megabyte (MB)

Capital B

Megabit (Mb)

Small b

The insight

B stands for byte and b stands for bit. That's the whole rule, and it's easy to skim past.

What it counts

Megabyte (MB)

Bytes

Megabit (Mb)

Bits

The basic unit

Megabyte (MB)

A byte: a group of 8 bits

Megabit (Mb)

A bit: a single 0 or 1

How big, in bits

Megabyte (MB)

8,000,000 bits

Megabit (Mb)

1,000,000 bits

How big is a rung on the ladder?

This track runs from 0 to 1 MB, counted in bytes, so the far end is 1,000,000 bytes. Where on it does 1 kB sit?

Your estimate

500000 bytes

This track runs from 0 to 1 MB, counted in bytes, so the far end is 1,000,000 bytes. Where on it does 1 kB sit? Estimate between 0 bytes and 1000000 bytes.

0 bytes1000000 bytes

1,000 or 1,024?

How many kilobytes are there in 1 MB? Pick the idea closest to what you think right now.

1,024 kB. I've definitely seen 1,024 used for this.1,000 kB. Mega is one step above kilo, and each step is ×1,000.100 kB. Metric prefixes go up in tens.1,000,000 kB. Mega means a million.

How sure are you?

I'm sureI think soI'm guessing

1,024 kB. I've definitely seen 1,024 used for this.

This is a common misconception

You're not imagining it. Historically, kilobyte, megabyte and the rest were often used to mean powers of 2, and 1,024 is a power of 2 (2 multiplied by itself ten times). But kilo and mega are decimal prefixes, from the SI system, and SI prefixes are based on powers of 10. With decimal prefixes, 1 MB is 1,000 kB, so that's the one to use.

1,000 kB. Mega is one step above kilo, and each step is ×1,000.

This matches the evidence

Yes. Kilo, mega, giga and tera are all decimal prefixes, and SI prefixes are based on powers of 10. So 1 kB is 1,000 bytes, 1 MB is 1,000 kB and 1 GB is 1,000 MB. The same ×1,000 step every time.

100 kB. Metric prefixes go up in tens.

This is a common misconception

Powers of 10 doesn't mean each step is ×10. It means the values are made by multiplying 10 by itself: 1,000 is 10 × 10 × 10. Each named step (bytes to kB, kB to MB, MB to GB) is ×1,000, so 1 MB is 1,000 kB, not 100.

1,000,000 kB. Mega means a million.

This is a common misconception

A megabyte is a million, but it's a million bytes, not a million kilobytes. Start from bytes: 1,000,000 bytes ÷ 1,000 = 1,000 kB. The million belongs to the smallest unit.

1 MB = 1,000 kB = 1,000,000 bytes. Decimal prefixes, powers of 10, and ×1,000 at every step.

Spot the slip

Which is bigger: 0.6 GB or 550 MB?

A student's answer — which line goes wrong?

The units are different, so I'll change 0.6 GB into megabytes first.
1 GB is 1,000 MB.
So 0.6 GB = 0.6 ÷ 1,000 = 0.0006 MB.
0.0006 MB is less than 550 MB.
So 550 MB is bigger.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

A thousand kilobytes, a million bytes, a thousandth of a gigabyte. Once you can hold that in your head, the megabyte becomes a yardstick you can measure anything against.

What you need to know

1 MB = 1,000 kB, and 1 kB = 1,000 bytes, so 1 MB = 1,000,000 bytes.
1 GB = 1,000 MB, so a megabyte is a thousandth of a gigabyte.
Kilo, mega, giga and tera are decimal prefixes: SI prefixes, based on powers of 10.
B means byte and b means bit. A byte is a group of 8 bits, and a bit is a single 0 or 1.

The big picture

A megabyte (MB) is 1,000 kilobytes, which makes it 1,000,000 bytes, and 1,000 megabytes make a gigabyte. Mega is a decimal prefix: like kilo, giga and tera, it's an SI prefix based on powers of 10. To compare amounts of data, get them into the same unit first, then compare the numbers. And watch the letter: B is bytes, b is bits, and a byte is 8 bits.

Key points

1To compare amounts of data, convert them all to one unit first, then compare the numbers.

2Moving to a smaller unit, the number gets bigger (× 1,000). Moving to a bigger unit, it gets smaller (÷ 1,000).

3Bits to bytes: divide by 8. So 8,000,000 b is 1,000,000 B, which is 1 MB.

4You may meet 1,024: historically these terms were often used for powers of 2. With decimal prefixes, 1 MB is 1,000 kB.

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Worked example

Problem

Put these in order, smallest first: 0.0015 GB, 1,300 kB, 9,000,000 b.

⚠ Watch out

Reading a small b as a capital B. 8,000,000 b is not 8 MB. It's bits, so divide by 8 first: 1,000,000 bytes, which is exactly 1 MB.

🧠

Memory hook

Three zeros per rung: bytes, kB, MB, GB, ×1,000 at every step. A small b has to be divided by 8 before it's allowed on the ladder.

✓

Check yourself

Is 0.0009 GB more or less than 1 MB? What about 8,800,000 b? Convert each one before you decide.

Flashcards

(13)

How many kilobytes are in 1 MB?

1,000 kB.

How many bytes are in 1 MB?

1,000,000 bytes (1,000 kB, each of 1,000 bytes).

How many bytes are in 1 kB?

1,000 bytes.

How many megabytes are in 1 GB?

1,000 MB. So 1 MB is a thousandth of a gigabyte.

What do B and b stand for?

B is byte. b is bit.

What is a byte?

A group of 8 bits.

What is a bit?

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

Name the four decimal prefixes used for quantities of bytes.

Kilo, mega, giga and tera.

SI prefixes such as kilo and mega are based on powers of what?

Powers of 10.

Why might you see 1 MB given as 1,024 kB?

Historically these terms were often used for powers of 2. With decimal prefixes, 1 MB is 1,000 kB.

How do you turn a number of bits into bytes?

Divide by 8, because a byte is 8 bits.

Converting GB to MB: multiply or divide by 1,000?

Multiply. MB is the smaller unit, so the number gets bigger.

Which is more data: 1 MB or 1 Mb?

1 MB. It's 8 times as much, because it counts bytes and 1 Mb counts bits.

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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Is it more than a megabyte?

How big is a rung on the ladder?

1,000 or 1,024?

Spot the slip

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