Layers of a social networking site?

[peteams]

Not just social media, but all kinds of web sites from Facebook through Amazon and Gmail follow roughly the same 'pattern'. (Pattern is a very current computing term.)

On a user's desktop they see the web site. That is comprised largely of three elements:
1. HTML is used to carry the content of the web site, so the words you are reading now.
2. CSS is used to style the web site, so the font and layout of the text you are reading is in CSS. (You can put the same information into the HTML, but that become harder the more complex the web site.)
3. JavaScript is used to do work in the browser, so driving the spell checker that comes up as you type text.

Those three groups of software are managed by the web browser. The web browser talks across the internet to a web server. It is the web server that is responsible for maintaining the connection and communication between the user's web session and the computers running the web site for everyone.

There are two common web servers, Apache and Microsoft IIS.

Inside the web server the actual web pages are created both by simply being fixed files, like.many of the graphic images on this page. Also pages are created dynamically by merging HTML templates with data from an application. Those applications can be written in many languages, Java and C# are common for complex business web sites, PHP and others for simpler ones.

The actual data used by the applications on the web server is normally stored in a relational database, that is a piece of software that knows how to store, organize and retrieve data well. MySQL, Oracle and SQL Server are common databases.

The web servers and database servers are often versions of desktop PCs. However these PCs have no screens, keyboards or other unnecessary parts, often just the processed, memory and power supply; many don't even have hard disks. These computers are stored in racks, each rack containing tens of computers in rooms that contain perhaps hundreds of racks. So a server farm may contain many thousands of computers.