Topics related to yours: Need to have some familiarity.
General Area: Might need to do additional reading/brushing up.
Example:
Topic: Super-scalar architectures
Related Topic: VLIW architectures
General reading: Architecture
Topic: Randomized Algorithm for problem X
Related Topic: Deterministic Algorithms
General reading: Algorithms, Probability theory
Familiarity = 1/(Distance from topic)
But you must be very familiar with the basics even if the topic is advanced.