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Key points

  • Data storage is measured in bits, and can be grouped into larger units of bytes, kilobytes, megabytes, gigabytes, terabytes, petabytes, exabytes, zettabytes and yottabytes.
    • A bit is a binary digit of 1 or 0
    • A byte is a group of 8 bits
    • A kilobytes is a group of 1024 bytes
    • A megabyte is a group of 1024 kilobytes
    • A gigabyte is a group of 1024 megabytes
    • A terabyte is a group of 1024 gigabytes
    • A petabyte is a group of 1024 terabytes
    • An exabyte is a group of 1024 petabytes
    • A zettabyte is a group of 1024 exabytes
    • A yottabyte is a group of 2014 zettabytes


Examples of storage sizes

  • Each character will take one or two bytes to store (one for ASCII codes, two for 16 bit Unicode)
  • An icon or a text file is likely to be a few bytes
  • Most graphics on a website will be a few hundred kilobytes in size.
  • Mobile apps, MP3s and photographs are often measured in megabytes
  • Games and HD video files are a few gigabytes in size due to the graphical data stored
  • A desktop computer will have several hundred gigabytes to a few terabytes of backing storage
  • The data transfer from major websites such as Google and the BBC is measured in petabytes per month
  • The data transfer of the entire Internet is measures in exabytes - in 2010 it was 21 exabytes per month, but this increases every year.
  • The entire contents of the World Wide Web was estimated to be 4 zettabytes in 2013
  • All the data stored digitally on earth does not currently add up to 1 yottabyte. It is thought by many technologists that the storage size of a yottabyte is still so big, that for a single storage facility to store a yottabyte of data in the future, there would need to be advancement in new forms of storage, such as DNA data storage (DNA data is estimated to store more than 500 terabytes per gram!)
  • A CD-ROM stores between 600 and 700 megabytes
  • A DVD-ROM can store between 4 and 17 gigabytes
  • A Blu-ray disc can store up to 40 gigabytes
  • A hard drive can store up to 4 terabytes
  • SD Cards can store up to 256 gigabytes


Further information

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Teaching resources