Is it recommended for a professor to not entertain advanced questions for a basic course? Recently I worked as a teaching assistant for a digital logic course. The topic for the day was full-adder. Professor explained the full concept of the full adder, along with question and answer session and then it is now the turn of TAs to clarify doubts of the students. One student asked me the question: what is the architecture of full adder circuit using currently in the most advanced CPU of laptops. I really had no clue about it. 

But a new doubt raised in my mind that how should a professor react to such questions? 

The professor may not know every aspect and every trend in the subject (s)he is teaching. If (s)he says that I don't know, then, the respect for the professor may go down. Else if (s)he says that it is beyond the scope of the course then the research aspirancy of the students may go down. Other methods are providing references later by saying I will send it to you/class later etc., but still, it is like saying I don't know, but indirectly. Because if one the student asks a question, then many people want to know the answer immediately from the professor. I feel that the professor should at least answer the question in a very short form. 

So, the final question can be divided into two parts:

1) How should a professor react to the most advanced questions from 
their students of a basic course, if (s)he knows the answer?

2) How a professor has to react in the classroom for the advanced questions that (s)he doesn't know the answer?
1) How should a professor react to the most advanced questions from her students of a basic course, if (s)he knows the answer?


I would distinguish between reasonable and obnoxious questions. 


If the question is reasonable, then I would give a concise answer and encourage "offline" follow up. The question in your example seems reasonable -- it's essentially "how wide is the gap between what we're learning and what's actually used?"
If the question is obnoxious (e.g., student is just trying to show off), then I would consider giving a very concise answer (one sentence), or else explaining that you don't think the question is a good use of the available time (and, optionally, encouraging follow up in office hours). 



  2) How a professor has to react in the classroom for the advanced questions that (s)he doesn't know the answer?


I'm not sure one has any choice but to say "That's a good question, but I have no idea" or "I have no idea, and I doubt it matters for the purpose of this exam."