V · Physics & hardware limits
Memory hierarchy
What it is
L1 ≈ 1 ns, L2 ≈ 4 ns, L3 ≈ 12 ns, RAM ≈ 100 ns, NVMe ≈ 100 µs, network ≈ 1 ms, disk ≈ 10 ms.
Where it lives
Why cache locality matters more than algorithmic complexity for small n. Why DB engines fight for page-cache.
The key insight
Each level is roughly 10× slower than the last. A pointer chase across cache levels can dominate any computation.