deadline vs. noop

[PetGhost]

On No-Frills CPU Control, a new option appeared which I don't remember ever seeing before. It asks me "I/O Scheduler" and my choices are "deadline," and "noop," defaulting to deadline. I have no clue what this means, and a quick search didn't find anything useful. I'm just curious as to what this means, and if I could get anything out of switching to noop? I may just try noop out for a day and see if I notice anything different.