The BEAM Book [1] is a good, though unfinished resource talking in general about the implementation - the memory model and the interpreter.
If you're interested in some very low-level details of the runtime, the internal documentation [2] also holds a lot of interesting details.
There are also some additional details on internals at Spawned Shelter [3].
[1]: https://blog.stenmans.org/theBeamBook/ [2]: https://github.com/erlang/otp/tree/master/erts/emulator/inte... [3]: http://spawnedshelter.com/#erlang-design-choices-and-beam-in...