NVIDIA Computer Architecture interview questions

3 rounds of interview, first two rounds are telephone call, each round one hour, third round is face to face interview which takes 4 hours, people in nvidia are nice and positive, they will lead you to the correct answer. The last interview guys ask the detail thing about what I have done in current company. The whole interview process are pleasant except the final result is frustrated

the process took 2+ month. I applier through career fair on campus and took a quiz there. after about two month I had my first phone interview mostly on C/C++ and Memories ( virtual memory and cache) and an algorithm question. had the second interview three weeks later. again on graphs, and some general questions on my resume( like what you learned from doing this project and that project), and memory questions. each interview took about 45 mins. I haven't heard anything from them yet.