Units of information: giga, 1 GB is 1,000 Megabytes

The idea

The prefix giga (symbol G) multiplies a unit by one thousand million, so 1 gigabyte (1 GB) is 1,000 megabytes (1 MB). This is a decimal, powers-of-ten relationship: 1 GB = 1,000 MB = 1,000,000 kB = 1,000,000,000 bytes. To convert gigabytes to megabytes, multiply by 1,000; to convert megabytes to gigabytes, divide by 1,000. For example, a 3 GB storage card holds 3 × 1,000 = 3,000 MB, and a 500 MB file is 500 ÷ 1,000 = 0.5 GB. Because giga is larger than mega, the same quantity has a smaller number when expressed in GB. In a multiple-choice question, check both the factor (1,000, not 1,024) and the direction of the conversion before selecting an option.

What earns the marks

• States that 1 GB = 1,000 MB, using the decimal factor of 1,000.
• Explains that giga means one thousand million, so 1 GB = 1,000,000,000 bytes.
• Converts gigabytes to megabytes by multiplying by 1,000 (e.g. 3 GB = 3,000 MB).
• Converts megabytes to gigabytes by dividing by 1,000 (e.g. 500 MB = 0.5 GB).
• Links the scale to the next unit down, recognising that 1 GB = 1,000 MB and 1 MB = 1,000 kB.

Common mistakes and how to put them right

• Using 1,024 as the factor.

  Put it right: The specification uses decimal units, so 1 GB is 1,000 MB, not 1,024 MB.

• Multiplying when converting MB to GB.

  Put it right: Dividing by 1,000 is correct because MB is the smaller unit.

• Confusing giga with mega.

  Put it right: Giga is one thousand million (1,000 MB), whereas mega is one million (1,000 kB).

• Thinking a larger number of MB means more data than the same quantity in GB.

  Put it right: 2,000 MB and 2 GB are equal.

Exam tips

• Write the factor (×1,000 or ÷1,000) beside the question before judging the options.
• Check the direction: converting to a smaller unit gives a larger number, so multiply.
• Reject any option using 1,024, since the specification treats these units as decimal.
• Verify a candidate option with a quick example, such as 2 GB = 2,000 MB, before choosing.