Computer Science Fundamentals

What this area actually covers

The core-subject rounds draw on four or five undergraduate courses: operating systems, computer networks, database theory, the object-oriented model, and how source code becomes running instructions. Within each, an interview reaches for a small and stable set of ideas — process versus thread and what a context switch costs, virtual memory mapping addresses that do not exist to pages that do, TCP's guarantees against UDP's absence of them, functional dependencies and what a transaction promises, and the phases between text and execution.

The boundary that matters is against system design. System design asks you to choose and arrange components; fundamentals ask you to explain why a component behaves as it does. "Put a cache in front of the database" is a design answer. "The cache helps because the working set fits in memory and a page fault costs several orders of magnitude more than a hit" is a fundamentals answer, and only one of them survives being asked why three times.

Data structures and algorithms are also frequently bundled in here and should not be. Sorting, trees and complexity analysis are their own round with its own format — you write code, and it either runs or it does not. Fundamentals questions are almost always verbal, which changes what a good answer looks like entirely.