Realm uses a custom C++ core that is different from SQLite, and we published a bit about the architecture here http://realm.io/news/introducing-realm/#fast http

Realm uses a custom C++ core that is different from SQLite, and we published a bit about the architecture here http://realm.io/news/introducing-realm/#fast http://realm.io/news/introducing-realm/#fast. Both iOS and Android API's are just wrappers around this core.