Units of Data Storage (OCR GCSE Computer Science)
Revision Note
Written by: Robert Hampton
Reviewed by: James Woodhouse
Units of Data Storage
Computers use binary numbers to represent data
Data such as characters, images and sound must be stored as binary
The smallest unit of data a computer can store is 1 binary digit, otherwise expressed as 1 bit
1 bit can only hold one value (21), this is not big enough to store all kinds of data, so computers have different 'Units of Data'
What are units of data?
A unit of data is a term given to describe different amounts of binary digits stored on a digital device
These are the units you need to know for GCSE:
Unit | Symbol | Binary | Written as | Example |
|---|---|---|---|---|
Bit | b | 1 or 0 |
|
|
Nibble |
| 4 b |
|
|
Byte | B | 8 b |
| A single character |
Kilobyte | KB | 1000 B (210) | Thousand bytes | A small text file |
Megabyte | MB | 1000 KB (220) | Million byes | A music file |
Gigabyte | GB | 1000 MB (230) | Billion bytes | A high definition movie |
Terabyte | TB | 1000 GB (240) | Trillion bytes | A large hard drive |
Petabyte | PB | 1000 TB (250) | Quadrillion bytes | A large data centre |
Examiner Tips and Tricks
Binary only contains two digits (1 and 0) so technically larger multiples would be calculated as 2number of bytes
For example, a kilobyte is 210 = 1024 bytes not 1000 bytes
In GCSE we approximate all larger units of storage as multiples of 1000 to make calculations easier
Converting between units
It is often a requirement of the exam to be able to convert between different units of data, for example bytes to megabytes (larger) or kilobytes to bytes (smaller)
This process involves division, moving up in size of unit and multiplication, moving down in size of unit
When dealing with all units bigger than a byte we use multiples of 1000
For example, 2000 kilobytes in megabytes would be 2000 / 1000 = 2 MB and 2 terabytes in gigabytes would be 2 * 1000 = 2000 GB
When dealing with bits and bytes the same process is used with the value 8 as there are 8 bits in a byte
For example, 24 bits in bytes would be 24 / 8 = 3 B and 10 bytes in bits would be 10 * 8 = 80 b
| Unit |
|
|---|---|---|
Multiply by 8 ⇑ | Bit | Divide by 8 ⇓ |
Byte | ||
Multiply by 1000 ⇑ | Kilobyte | Divide by 1000 ⇓ |
Megabyte | ||
Gigabyte | ||
Terabyte | ||
Petabyte |
Worked Example
Computers represent data in binary form.
Tick one box in each row to identify the binary unit equivalent of each of the given file sizes [4]
Answer
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