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2.3: Data Units

Exam Board:


Why data must be stored in binary format

How data needs to be converted into a binary format to be processed by a computer

text file size = bits per character x number of characters

All computer systems communicate, process and store data using binary.


Binary is a number system consisting entirely of 0s and 1s.


Why do computers use binary?

Computer systems consist of billions of tiny transistors which are switches that only have two values - on (1) or off (0). Therefore all data must be represented and processed in this way.

Everything that a computer needs to process must be converted into a binary format including text, images, videos and audio.

0010 1011 0101 0101 0110 0111 0101 0001 0101 0101 0101 0100 1010 1010 1010 1010 1111 1110 0010 1001 0100 1001 0010 0111 0111 0101 0011 1010 1000 0101 0110 0111 0000 1010 1010 0011 1101 1001 0010 1101 0010 0100 1001 0011 1010 1001 0101 0101 0010 0101 0111 0101 0101 1000 1011 0111

Units of Data Storage

0 / 1

All data in a computer system is made up of bits.

A single bit is a 0 or a 1.

4 bits (such as 0101 or 1101) is called a nibble.

1,000 bytes is called a kilobyte.

A kilobyte can store a short email.


8 bits is called a byte.


A byte can store a single character.

1,000 kilobytes is called a megabyte.

A megabyte can store about a minute of music.

1,000 megabytes is called a gigabyte.

A gigabyte can store about 500 photos.

1,000 terabytes is called a petabyte.

A petabyte can store about 1.5 million CDs.

1,000 gigabytes is called a terabyte.

A terabyte can store about 500 hours of films.

This video shows some real-world examples to help you understand the scale of the different data storage units.

Important note - this video was originally made for a different exam board and uses a scale of 1,024 between data units. 

Technically 1,000 bytes is a kilobyte. 1,024 bytes is a kibibyte

In the OCR GCSE exam you can use either 1,000 or 1,024 but as it is a non-calculator paper it makes sense to use 1,000 for simpler calculations.

Calculating Data Capacity Requirements

It is important to be able to calculate the required storage capacity for a given set of data.


A local DJ has a USB memory stick with a capacity of 32GB. There is currently only 9GB of space remaining

Each song is 6MB. How many songs can be stored on the remaining space of the USB stick?


Because each song is recorded in megabytes but the USB stick capacity is measured in gigabytes, the values must be converted into the same storage unit.

9GB x 1000 = 9000MB

9000MB ÷ 6MB = 1,500 songs

Watch on YouTube

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Questo's Questions

2.3 - Data Units:

1. Explain why computer systems use binary to represent data. [2]

2. Put the following data storage units in order from smallest to largest: 

  • a. kilobyte - gigabyte - byte - megabyte - nibble - bit [3]

  • b. gigabyte - petabyte - kilobyte - byte - terabyte - megabyte [3]

3. A hard drive contains 25GB of remaining available storage space. Tim is an animator backing up video files. Each file is 200MB. How many files can he fit on the hard drive? [2]

4. Samantha is a musician. She has compressed each song to 900KB. Her USB memory stick contains 1.2GB of free storage. How many songs can she fit on the USB stick? [2]

5. A CD has a capacity of 650MB. How many 0.2GB audio files can be stored on the CD? [2]

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