system
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human
I need to understand servers well enough to explain the concept to my boss...

Hi wise reddit friends,

Let me start off by saying that, while I'm not a computer illiterate person, I don't work in the IT realm and I don't understand this concept as well as I would like.
Preamble: Imagine there are 3 sites, each with their own local database sitting on their own SQL server (which I'm also not entirely sure how to explain). 
These sites will be uploading data to a joint server.
This is the part I don't quite get: I am told we need two servers: one to host the data itself and another server to host the website that will allow access to the first server. 

Am I getting this right? 
Why do you need two servers though? Can't you just use one?

Thanking you in advance.
gpt
On the technical side, you *can* run the database management software and the web server on the same server. But it makes the database too accessible, so it's considered a pretty big security risk. 

Speaking loosely, a web server is supposed to accept connections from everybody in the world.  A database server is *not*. Like *hell not*.

So it's really rare for anyone to recommend putting both on a single machine. Instead, you'll usually run the database management software on a separate machine--ideally, a machine that handles nothing but the database--behind a firewall, probably requiring encrypted connections, and probably configured to accept connections from only the web server. (Or from the web server and from other computers on the local area network--but not from just any random IP address.)

But . . .

If you have a computer that can run at least two virtual servers, you can run the web server on one virtual server, and run the dbms on the other virtual server. (Thanks, and a tip of the hat to macwiz1220 for the reminder.)

If you have to comply with the Payment Card Industry (PCI)
Data Security Standard (PCI DSS), you can't run both the web site and the dbms on one server. But, again, if you have a computer that can run at least two virtual servers, you can run the web server on one virtual server, and run the dbms on the other virtual server. (This can make PCI DSS auditing and compliance more complicated, though.)