Be able to compare quantities of bytes using the prefixes above.

The idea

Comparing byte quantities means converting every value to the same prefix, usually the smallest one present, then ordering them. Use the decimal ladder: kilo = 10³, mega = 10⁶, giga = 10⁹, tera = 10¹². Each step up multiplies by 1,000, so 2 GB = 2,000 MB = 2,000,000 kB. To compare 500 MB with 0.4 GB, convert 0.4 GB to 400 MB; 500 MB is therefore larger. To compare 1.5 TB with 1,400 GB, convert 1.5 TB to 1,500 GB, which is larger than 1,400 GB. Always convert before comparing, keep the units labelled, and check the direction of each conversion so the larger prefix gives the smaller number for equal storage.

What earns the marks

• Convert each quantity to a common prefix before comparing, for example expressing all values in MB or all in GB.
• Apply the decimal factors: 1 kB = 1,000 B, 1 MB = 1,000 kB, 1 GB = 1,000 MB, 1 TB = 1,000 GB.
• Order or select quantities correctly once converted, for example 500 MB is greater than 0.4 GB.
• Recognise that a larger prefix means a smaller numerical value for the same storage.
• Keep units attached to each value throughout the comparison to avoid mixing prefixes.

Common mistakes and how to put them right

• Comparing the numbers without converting, so 0.4 GB looks smaller than 500 MB when it is actually 400 MB.

• Using 1,024 instead of 1,000 between prefixes.

  Put it right: The specification's prefixes are decimal.

• Losing the unit label partway through and treating a GB value as if it were MB, which reverses the comparison.

Exam tips

• Convert every value to the smallest prefix in the list first, then compare the resulting numbers.
• Write the conversion factor next to each step, for example ×1,000 going from GB to MB, so the direction is clear.
• Check your answer by asking whether the larger-prefix value should have the smaller number for the same storage.