I've been looking into writing an emulator for a while now. There are some excellent references for specific systems, but one of the best sources I've found is

I've been looking into writing an emulator for a while now. There are some excellent references for specific systems, but one of the best sources I've found is here: http://www.codeslinger.co.uk/pages/basics.html http://www.codeslinger.co.uk/pages/basics.html In addition to having source code for several different emulators, they've written a ~150 page document about emulator development. It's easily the best resource I've seen on the subject.