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 |
Exam 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]
File size | 4 megabytes | 24 bits | 5 kilobytes | 10 bytes | 2 terabytes |
2000 gigabytes | |||||
5000 bytes | |||||
6 nibbles | |||||
3 bytes |
Answer
File size | 4 megabytes | 24 bits | 5 kilobytes | 10 bytes | 2 terabytes |
2000 gigabytes | |||||
5000 bytes | |||||
6 nibbles | |||||
3 bytes |