I received an email indicating I was to have an on-site interview. I was flown to the facility. The interview consisted of architectural, software, behavioral, and debug questions. The questions were relatively easy consisting of basics taught in your computer architecture and computer science classes. Some specific questions regarding Intel architecture were asked. The interviews were back-to-back with a one hour break for lunch.
Definitely a long, intensive, and exhausting interview process. If you know your stuff and are a good communicator it should not be a big problem.