Pearson Edexcel · GCSE · Computer Science
Course version: 1CP2 · Version from Sept 2020
Understand that data storage is measured in binary multiples (bit, nibble,…
Full specification wording
Data storage and compression: 2.3.1 understand that data storage is measured in binary multiples (bit, nibble, byte, kibibyte, mebibyte, gibibyte, tebibyte) and be able to construct expressions to calculate file sizes and data capacity requirements
Data storage is measured in binary multiples, each a power of two times the previous unit.
Checked against the Pearson Edexcel 1CP2 specification (opens in a new tab) on .
- Point 1 of 2
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Data storage is measured in binary multiples, each a power of two times the previous unit. A bit is one binary digit; a nibble is 4 bits; a byte is 8 bits. The larger units step by 2¹⁰ = 1024: 1 kibibyte (KiB) = 1024 bytes, 1 mebibyte (MiB) = 1024 KiB = 1 048 576 bytes, 1 gibibyte (GiB) = 1024 MiB, and 1 tebibyte (TiB) = 1024 GiB. To calculate a file size or capacity requirement, multiply the number of items by the bits or bytes each item needs, then convert to the requested unit by dividing by the appropriate power of 1024. For example, an image of 800 × 600 pixels at 24 bits per pixel needs 800 × 600 × 24 = 11 520 000 bits, which is 11 520 000 ÷ 8 = 1 440 000 bytes, or about 1.37 MiB. Always state the unit and keep the direction of each conversion correct.
What earns the marks
- A bit is a single binary digit and a nibble is exactly 4 bits, so a byte (8 bits) equals two nibbles.
- Binary multiples increase by a factor of 1024 (2¹⁰): 1 KiB = 1024 bytes, 1 MiB = 1024 KiB, 1 GiB = 1024 MiB, 1 TiB = 1024 GiB.
- A file-size expression multiplies the number of items (for example pixels, samples or characters) by the bits or bytes required per item.
- Converting between units divides or multiplies by the correct power of 1024, and the answer must carry the correct unit such as bits, bytes, KiB or MiB.
Common mistakes and how to put them right
Treating binary multiples as powers of 1000.
Put it right: Use 1024, because these are binary multiples.
Confusing bits with bytes.
Put it right: Divide the bit total by 8 before converting to KiB or MiB.
Multiplying when a division is needed.
Put it right: Divide by 1024 when moving to a larger unit and multiply when moving to a smaller unit.
Exam tips
- Write the expression before evaluating it, for example pixels × bits per pixel ÷ 8, so the method is visible even if the arithmetic slips.
- Convert in clear steps and cancel powers of 1024 one at a time, checking whether the answer should grow or shrink.
- Give the unit with every value and check the question's requested unit before selecting your final option.
Try the lesson
The start of the Data storage and compression: 2.3.1 understand that data storage is measured in binary multiples (bit, nibble, byte, kibibyte, mebibyte, gibibyte, tebibyte) and be able to construct expressions to calculate file sizes and data capacity requirements lesson, made from checked teaching notes for this specification point.
Have a go first
A text file is 3 bytes in size. How many bits does the file contain?
Listen
Data storage is measured in binary multiples, each a power of two times the previous unit. A bit is one binary digit; a nibble is 4 bits; a byte is 8 bits. The larger units step by 2¹⁰ = 1024: 1 kibibyte (KiB) = 1024 bytes, 1 mebibyte (MiB) = 1024 KiB = 1 048 576 bytes, 1 gibibyte (GiB) = 1024 MiB, and 1 tebibyte (TiB) = 1024 GiB. To calculate a file size or capacity requirement, multiply the number of items by the bits or bytes each item needs, then convert to the requested unit by dividing by the appropriate power of 1024. For example, an image of 800 × 600 pixels at 24 bits per pixel needs 800 × 600 × 24 = 11 520 000 bits, which is 11 520 000 ÷ 8 = 1 440 000 bytes, or about 1.37 MiB. Always state the unit and keep the direction of each conversion correct. A strong answer earns marks for these points. A bit is a single binary digit and a nibble is exactly 4 bits, so a byte (8 bits) equals two nibbles. Binary multiples increase by a factor of 1024 (2¹⁰): 1 KiB = 1024 bytes, 1 MiB = 1024 KiB, 1 GiB = 1024 MiB, 1 TiB = 1024 GiB. A file-size expression multiplies the number of items (for example pixels, samples or characters) by the bits or bytes required per item. Converting between units divides or multiplies by the correct power of 1024, and the answer must carry the correct unit such as bits, bytes, KiB or MiB. A common slip: Treating binary multiples as powers of 1000: the error is using 1000 bytes per kibibyte. Instead, use 1024, because these are binary multiples. Exam tip: Write the expression before evaluating it, for example pixels × bits per pixel ÷ 8, so the method is visible even if the arithmetic slips.
Key words
Say what each word means before you turn the card.
Binary multiples
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Nibble
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File-size expression
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Unit conversion
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See every definition
- Binary multiples
- Units of data storage that each increase by a factor of 1024, which is 2¹⁰, from the previous unit.
- Nibble
- Exactly 4 bits, so that a byte of 8 bits equals two nibbles.
- File-size expression
- A calculation that multiplies the number of items by the bits or bytes required per item.
- Unit conversion
- Dividing or multiplying by the correct power of 1024, keeping the direction correct and stating the unit.
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