system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a database handle 1 billion users?

I'm really interested in how companies store such HUGE amounts of data but somehow retrieve and display the information in <1s.

I was looking at my Facebook activity for 2010 and it has the thousands upon thousands of posts I liked. You can't possibly store this in some sort of pivot table database, could you? Facebook would have literally 800 billion rows.

And my actual question is, how does a company, like Facebook, store more than 1 billion credentials? Is it split into regions like Users_GB, Users_US?

I work as a web developer. But as I work for a small company, I just can't fathom data this big.

Any insider knowledge, anecdotes and discussion from anyone who works on large databases would be appreciated. 

Edit: Went to bed, woke up and the blew up. Thanks for all the great discussion, and thanks for the gold.
gpt
The good news is that data isn't stored in one giant table.  It is actually made up of multiple tables.  Tools exist that then link those tables and read the information in them fairly effeciently.  Oracle, MySQL, etc handle massive amounts of data pretty easily.  Because these tools don't actually care what the data is, they just need the reference points, they can quickly retrieve the data.  
  
Think of how RAM works: fast switching pointers.  This is how you get a user's data out of billions in a table.  The software doesn't need to know that the person's first name is JOHN, it just needs to know that that user's pointer is here and it points to that table and then that table points to the next connected bit of data, etc.  It is a chain of tables.  Again, most of the retreival of the data isn't getting ALL of the data, it is just getting the pointer.  That pointer leads to the next pointer, and so forth.  Just fast swapping pointers and then one DISPLAY of the data.  
  
Big Data as it is termed, is a huge industry specifically for this challenge.  It isn't perfect, but an entire industry exists simply to find better ways to store data so that that pointer chain can be processed faster and faster.