Facebook is known as using LAMP as their basic platform for their website. One of the outstanding things Facebook doing very well is that they have their own strategy/architecture based on LAMP. LAMP stands for Linux + Apache + MySQL + PHP that is entirely free and open sourced software, so they can compete with their competitors in competitive operation cost with high-avail-abilities. In person, I think their strategy is pretty much innovative and its status tells their strategy is on the right direction.

One of the competitive component Facebook has is HipHop for PHP.

• PHP is a good programming language with extensive support, active developer community and rapid interaction. It is a dynamically typed language(interpreter).
• Facebook said that their HipHop is a source code transformer that converts the PHP into C++ and compiles it using g++, thus providing a high performance templating a web logic execution layer.

Facebook is also using MemCached to cache data and objects in RAM to reduce reading time. Facebook partitioned MemCached to maximize performance, so they can get their planned performances by divide and conquer.

Thift is a lightweight remote procedure called framework for scalable cross-language services development that supports C++, PHP, Python, Pearl, Java, Ruby, Erlang, ....

Reference

http://blog-bhaskaruni.blogspot.com/2012/12/facebook-architecture.html