Here's a link to an article that came out a little bit ago around the 30 year anniversary for the NES. We were talking about emulators for the system and some of the crazy hardware details came up, this article in the later pages has some details about the pretty basic hardware that made up the NES. There are emulators that are pretty high quality now, FCEUX is likely the best, but there's still some challenge in fully emulating all features of all game cartridges even on stupid fast computers today. Anyhow, the article has some fun to revisit stuff if you played a lot of NES, or maybe it will be interesting as an archeology exploration for the younger among us.
http://arstechnica.com/gaming/2013/07/time-to-feel-old-inside-the-nes-on-its-30th-birthday/
-Fulbert