Data Storage Units (Bit, Nibble, Byte, KB, MB, GB, TB, PB)

Understanding data storage units and being able to convert between them is a fundamental requirement for OCR J277 Section 2.6. This lesson covers all the units you need to know and how to convert between them.

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The Basic Units

Unit	Symbol	Size
Bit	b	The smallest unit of data — a single 0 or 1
Nibble	—	4 bits (half a byte)
Byte	B	8 bits

A bit is a single binary digit. A nibble is 4 bits (one hexadecimal digit). A byte is 8 bits (two hexadecimal digits) and is the standard unit of data storage.

OCR Exam Tip: Note the difference between lowercase 'b' (bit) and uppercase 'B' (byte). This distinction matters in technical specifications, especially for network speeds (measured in bits per second) vs storage (measured in bytes).

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Larger Units

Each subsequent unit is 1024 times the previous one (because 2^10 = 1024):

Unit	Symbol	Size in bytes	Power of 2
Kilobyte	KB	1,024 bytes	2^10
Megabyte	MB	1,048,576 bytes	2^20
Gigabyte	GB	1,073,741,824 bytes	2^30
Terabyte	TB	~1.1 trillion bytes	2^40
Petabyte	PB	~1.1 quadrillion bytes	2^50

Conversion Multipliers

From	To	Operation
Bits	Bytes	Divide by 8
Bytes	KB	Divide by 1024
KB	MB	Divide by 1024
MB	GB	Divide by 1024
GB	TB	Divide by 1024
TB	PB	Divide by 1024

To go in the opposite direction (e.g., KB to bytes), multiply by 1024 instead.

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Real-World Examples

Unit	Approximate real-world equivalent
1 bit	A single on/off switch
1 byte	A single ASCII character
1 KB	A short text message (~1,024 characters)
1 MB	A 1-minute MP3 audio file
1 GB	About 250 MP3 songs
1 TB	About 250,000 MP3 songs or 500 hours of video
1 PB	About 1,000 TB — used by large data centres

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Conversion Examples

Example 1: Convert 4,096 bytes to KB

4,096 / 1024 = 4 KB

Example 2: Convert 3 MB to bytes

3 x 1024 = 3,072 KB 3,072 x 1024 = 3,145,728 bytes