There is an ability to hold ideas in the mind simultaneously. Some can hold a great deal more than others. It can be exercised, but is definitely bound by genetics.

If you want an example of someone at the near peak of human ability, check out Jon Von Neumann.

Then there is an ability to peer deeply into complex problems and somehow find the simplest truths that make sense of it all. Think of Einstein.

Both are incredibly intelligent, but in different ways. I'd say Von Neumann's memory was far greater than Einstein's though.

One can flawlessly ponder anything known to man, and the other could ponder completely original ideas (to an extent)