All are surprised about facebook working. Facbook is so fast and simple to use. Software developers are very interested to know about,what happening behind the facebook. About half billion users are around the world but never feel this for the users. They are very much successfull in this fast running of facebook. The major concept using by facebook is Caching.According to the details, these are the technologies are using by facebook .
Main programming language is PHP but they have their own compiler so all most using their own native codes in webservers,it gives high performance.
The operating system is highly customized and optimized linux, for its own purposes,specially in the case of network throughput.
The back-end of facebook is MySQL, but it uses a key-value persistent storage so results high performance
Facebook using custom written systems like haystack(used for high storage of photos,posts,login..etc)
Facebook is using some custom softwares to become number one in social networking platform.
1. Memcached 2 .HipHop for PHP 3. Haystack 4. Bigpipe 5. Cassendra 6. Scribe 7. Thrift 8. Varnish 9. Handoop and Hive
These are major ones used by facebook other than this facebook using 1000s of small softwares to get performance.