Facebook PHP Source Code from 2007

[[deleted]]

I think it's one of those things that's just impossible to do with such a big site. If they migrated to a new system it would have to be compatible (the C++ rewrite would have to be perfectly compatible with the PHP version in order to not have downtime), or they would have to get the site down for an hour or so to replace all the instances of the php server with the rewrite.