Realm is not an ORM, but rather an integral part of your language. One key difference is that it does not have to copy all values in the objects back and fourth as you read them and save them, as most ORM's does. So that gives a huge performance improvement.

There are some benchmarks in our intro blogpost[0]. So I can recommend reading that for a bit more background information. We will have more blog posts coming out soon about the technical details.

[0] http://realm.io/news/introducing-realm/