When you see open any image on Facebook it is opened in the same window. Right ? But when you open it in a new tab (
Right Click -> Open Image In A New Tab) you will see
fbcdn.net in your URL bar. So what is
fbcdn.net ? Why facebook is using other domain name for their photos ? If you already know then read other tutorials and if you don't then read on...
Whats The Matter Here ?
The photos which you upload to facebook, are actually being uploaded to
fbcdn.net. Now the question arises, What is
fbcdn.net and Why your photos are hosted on
fbcdn.net ?
What Is fbcdn.net ?
Here facebook is actually using Akamai Technologies CND (Content Delivery Network). So this is your final answer if you know what is a CND and how it works. Others read on..
What is a CDN ?
According to Wikipedia -
"A content delivery network or content distribution network (CDN) is a large distributed system of servers deployed in multiple data centers across the Internet. The goal of a CDN is to serve content to end-users with high availability and high performance".
So simply a CDN (content delivery network) will receive your data and place it on several different servers all over the world. This makes that particular content to load faster for anyone who wants to access it. This is because the content will be delivered to the end user from the nearest possible server holding the content.
Why Facebook Photos Are Uploaded To fbcdn.net ?
Akamai has several CDN networks, where fbcdn.net is one of the CDN. Facebook is a large network and it has to deliver content at much faster speeds to each and every user. And to do so, it requires a CDN.
Facebook uses fbcdn.net as CDN. This is why your photos are uploaded to fbcdn and not to facebook. So whenever you request to view a photo on facebook, your request is actually sent to the nearest possible Akamai server. This server returns the requested photo. And since its the nearest possible server, you will get the requested photo with a minimum time delay.
Facebook is also using Akamaihd.net and may be some other URL also.