How Big Companies Manage Such Volume of Data?

So our first question is , what is data:Well according to Wikipedia-Data are characteristics or information, usually numerical, that are collected through observation. In a more technical sense, data are a set of values of qualitative or quantitative variables about one or more persons or objects, while a datum (singular of data) is a single value of a single variable.
In short Everything we observe is data ,What we see ,taste, our observations and much more.
So How big Volume of Data is there in Real world :Well According to many articles online for last few years there is a huge wave of data in real world,For example We as users upload around 500+ TeraByte of data which inlcudes post, photos, blogs,videos,comments,likes as well as shares also. So How Facebook is able to store as well as process such amount of Data
In reality It cost very much to Use big Storage Devices ,Reliable Hardware and Fast Resources.One more example is there are around 6000 tweets every second, which calculates to over 350,000 tweets per minute and 50 million tweets per day which really is an amazing number So to handle this Type of data as Well to process such data fast we introduce the concept Distributed Storage and to implement the concept of distributed storage we use Hadoop(Software)
Every Field whether it is Medical ,Stock market ,Mobile and Communications, IT industry ,E-commerce We use Hadoop.