In a virtual memory system, random access to an array of size n takes O(log n) time, and the constant factors in that O(log n) are also nontrivial. Algorithms that do O(log n) computation with O(log n) independent elements tend to take O(log^2 n) time, while those that do O(log n) computation with O(log n) contiguous elements or O(log n) iterations with O(1) elements still take O(log n) time. If the constant factors are small enough, it can be hard to distinguish the latter two from algorithms doing O(1) computation with O(1) elements.