Units of Data (AQA GCSE Computer Science)

Revision Note

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Units of Data

  • 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

 

 

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

Examiner Tip

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]

A table with a blue header has columns labeled: 4 megabytes, 24 bits, 5 kilobytes, 10 bytes, 2 terabytes. Rows include 2000 gigabytes, 5000 bytes, 6 nibbles, 3 bytes.

Answer

Table with file size and memory size columns. Rows show 2000 gigabytes (2 terabytes), 5000 bytes (5 kilobytes, 10 bytes), 6 nibbles (24 bits), and 3 bytes.

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