Units of information: kilo, 1 kB is 1,000 bytes

The idea

This row fixes the value of the kilo prefix for units of information: kilo means ×10³, so 1 kB is 1,000 bytes. Build the ladder from that anchor: 1 MB is 1,000 kB, which is 1,000,000 bytes, and 1 GB is 1,000 MB, which is 1,000,000,000 bytes. To convert, decide the direction first. Going to a larger unit divides by 1,000 each step, so 4,500 bytes is 4.5 kB. Going to a smaller unit multiplies by 1,000 each step, so 2 MB is 2,000 kB. A multiple-choice question may offer a distractor using 1,024; reject it because this specification uses the power-of-10 value.

What earns the marks

• Kilo is a power-of-10 prefix meaning ×10³.
• 1 kB equals 1,000 bytes.
• 1 MB equals 1,000 kB, which is 1,000,000 bytes.
• 1 GB equals 1,000 MB, which is 1,000,000,000 bytes.
• Converting to a larger unit divides by 1,000 per step; converting to a smaller unit multiplies by 1,000 per step.

Common mistakes and how to put them right

• Choosing 1,024 bytes for 1 kB.

  Put it right: For this specification 1 kB is 1,000 bytes, because kilo is a power-of-10 prefix.

• Multiplying when converting from bytes to kilobytes.

  Put it right: Moving to a larger unit divides by 1,000, so 3,000 bytes is 3 kB.

• Losing a factor of 1,000 when jumping two steps, for example treating 1 GB as 1,000 bytes.

  Put it right: Each step is ×1,000, so 1 GB is 1,000,000,000 bytes.

Exam tips

• Write the ladder byte → kB → MB → GB with ×1,000 between each rung before you start calculating.
• Convert to bytes first when a question mixes units, then divide or multiply to reach the unit asked for.
• Check the direction of your conversion by asking whether the number should get bigger or smaller.