Kōkiri Learn

Background reading · Technology

Ones, zeros and the data trail you leave

What data is, how computers store words and pictures using only on and off, and why metadata matters.

Data is any fact that has been recorded: the number of tūī in a tree, the time your bus arrived, the score in your last game. People have collected data for thousands of years with tally marks and notebooks. In 1890, Herman Hollerith built a machine that read holes punched in cards to count the United States census. Counting that once took years was finished in months. Today your phone collects more data in a day than that machine saw in its whole life.

Everything is on or off

Inside a computer are billions of tiny switches that can only be on or off. We write on as 1 and off as 0. Each 1 or 0 is called a bit. Eight bits together make a byte. With just ones and zeros, a computer can store numbers, words, pictures and sounds.

Turning things into numbers

  • Numbers: in binary, each place is worth double the one to its right (1, 2, 4, 8, 16…). So 1011 means 8 + 2 + 1 = 11. - Letters: every letter has a number code. Capital A is 65, which is 01000001 in binary. Letters with macrons, like ā, need a longer code. - Pictures: a photo is a grid of tiny squares called pixels. Each pixel's colour is stored as three numbers for red, green and blue. - Sound: a microphone measures the sound wave thousands of times a second and stores each measurement as a number.

    • Making files smaller

    Photos and songs use a lot of bytes. Compression makes files smaller. Some compression loses nothing: instead of storing 'white, white, white, white', it stores '4 white'. Other kinds, like JPG photos and MP3 songs, throw away detail your eyes and ears barely notice. That is a trade-off: a smaller file, but lower quality.

    Data about data

    Metadata is data that describes other data. When you take a photo, your phone may also save the date, the time, the type of phone and even the exact place you stood. That makes photos easy to search and sort. It also means a photo shared online can reveal where you live or go to school. Many apps let you turn location saving off.

    Your data trail

    Everything you do online can leave a trail. Posts can last a long time, be searched, be copied and be seen by people you never meant to show. Before you share, ask: would I be happy for anyone to see this in five years?

    Sources and further reading

    Written for Kōkiri Learn students in our own words. Check facts against the sources.

    Used in: Data Detectives: Data, Spreadsheets and AI