By far my favorite question to ask (and be asked) in an interview. As others point out, it's practically impossible to understand the entire system. At one point or another in my career I've been exposed to at least descriptions of most of the components, but if I wanted a processor engineer, I'd be looking for a different answer than a web developer, or a networking guy, etc. Essentially anyone involved in the modern world of IT has to be able to answer something they're good at - and more importantly, admit the parts they don't understand. You can't cheat your way through the question, hell, you could even know it's coming and you still can't "beat" it. You don't know if I'm looking for hyper-detail about something, business sense to skip over irrelevant (to the position) details of a certain level, etc.