OCR · GCSE · Computer Science
Course version: J277 · Version from Sept 2022
The units of data storage Bit Nibble (4 bits) Byte (8 bits) Kilobyte…
Full specification wording
Units: The units of data storage Bit Nibble (4 bits) Byte (8 bits) Kilobyte (1,000 bytes or 1 KB) Megabyte (1,000 KB) Gigabyte (1,000 MB) Terabyte (1,000 GB) Petabyte (1,000 TB)
Data storage is measured in a ladder of units, each step multiplying by 1,000 in this specification.
Checked against the OCR J277 specification on .
- Point 1 of 3
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Data storage is measured in a ladder of units, each step multiplying by 1,000 in this specification. A bit is one binary digit, 0 or 1. A nibble groups 4 bits, useful because one hexadecimal digit represents exactly one nibble. A byte groups 8 bits and typically stores one character. From bytes upward the units step by 1,000: 1 KB = 1,000 bytes, 1 MB = 1,000 KB, 1 GB = 1,000 MB, 1 TB = 1,000 GB and 1 PB = 1,000 TB. To convert, multiply when moving to a larger unit's worth of smaller units, and divide when moving the other way. For example, 3 MB = 3 × 1,000 KB = 3,000 KB = 3,000 × 1,000 bytes = 3,000,000 bytes. A 2 TB drive holds 2,000 GB, or 2,000,000 MB.
What earns the marks
- States that a bit is a single binary digit, either 0 or 1, and is the smallest unit of data.
- States that a nibble is 4 bits and a byte is 8 bits, and that a byte commonly represents one character.
- Recalls the 1,000 multiplier between consecutive units: KB, MB, GB, TB and PB.
- Converts between units correctly, multiplying when moving to smaller units and dividing when moving to larger units.
- Uses the units accurately in context, for example estimating that a 4-minute song file is a few MB while a film is several GB.
Common mistakes and how to put them right
Writing that 1 KB = 1,024 bytes.
Put it right by using the specification value of 1,000 bytes for OCR J277.
Confusing bits with bytes when converting, for example treating 8 Mb as 8 MB.
Put it right by noting that a lowercase b often means bit and an uppercase B means byte, and that 8 bits make 1 byte.
Multiplying when converting from a smaller unit to a larger unit, for example saying 5,000 MB = 5,000,000 GB.
Put it right by dividing by 1,000 at each upward step, giving 5 GB.
Exam tips
- Write the conversion ladder (bit, nibble, byte, KB, MB, GB, TB, PB) at the start of a calculation question so each step is visible.
- Show every multiplication or division by 1,000 as a separate line so method marks can be awarded even if the final value is wrong.
- Check the direction of conversion by asking whether the number should get bigger (moving to smaller units) or smaller (moving to larger units).
Try the lesson
The start of the Units: The units of data storage Bit Nibble (4 bits) Byte (8 bits) Kilobyte (1,000 bytes or 1 KB) Megabyte (1,000 KB) Gigabyte (1,000 MB) Terabyte (1,000 GB) Petabyte (1,000 TB) lesson, made from checked teaching notes for this specification point.
Have a go first
How many bits are there in one nibble?
Listen
Data storage is measured in a ladder of units, each step multiplying by 1,000 in this specification. A bit is one binary digit, 0 or 1. A nibble groups 4 bits, useful because one hexadecimal digit represents exactly one nibble. A byte groups 8 bits and typically stores one character. From bytes upward the units step by 1,000: 1 KB = 1,000 bytes, 1 MB = 1,000 KB, 1 GB = 1,000 MB, 1 TB = 1,000 GB and 1 PB = 1,000 TB. To convert, multiply when moving to a larger unit's worth of smaller units, and divide when moving the other way. For example, 3 MB = 3 × 1,000 KB = 3,000 KB = 3,000 × 1,000 bytes = 3,000,000 bytes. A 2 TB drive holds 2,000 GB, or 2,000,000 MB. A strong answer earns marks for these points. States that a bit is a single binary digit, either 0 or 1, and is the smallest unit of data. States that a nibble is 4 bits and a byte is 8 bits, and that a byte commonly represents one character. Recalls the 1,000 multiplier between consecutive units: KB, MB, GB, TB and PB. Converts between units correctly, multiplying when moving to smaller units and dividing when moving to larger units. A common slip: Writing that 1 KB = 1,024 bytes. Instead, using the specification value of 1,000 bytes for OCR J277. Exam tip: Write the conversion ladder (bit, nibble, byte, KB, MB, GB, TB, PB) at the start of a calculation question so each step is visible.
Key words
Say what each word means before you turn the card.
Bit
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Nibble
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Byte
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Kilobyte
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See every definition
- Bit
- A single binary digit, either 0 or 1, and the smallest unit of data.
- Nibble
- A group of 4 bits, useful because one hexadecimal digit represents exactly one nibble.
- Byte
- A group of 8 bits that typically stores one character.
- Kilobyte
- A unit of 1,000 bytes, or 1 KB, the first step above the byte in the ladder of units.
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