I'm one of those who use Facebook more or less daily and I'm always amazed about the speed and availability of facebook. They are using PHP. If Facebok is running PHP on their site it says alot of PHP and the power of this small and simple language. Combine this with cache it's one of the best languages for the web.

I read an article on their developerblog about how they have changed the way they serve all users. Facebook have deloped a PHP compiler and named it HipHop. Simple way of explaining this is that it compiles PHP to C++ and then runned as a webserver.

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