- attacker determining "attackability" of target ("can you hit your target from where you are?")
- attacker determining if attack is successful ("did you hit your target?")
- attacker determining if attack manages to do damage ("did you penetrate the armor?")
- attacker determining how much damage is done ("how badly did you hurt the target?")
Of course, the stages are already abstractions in themselves, and the amount of time spent doing each is dependent on how the rules are stated and interpreted.
In D&D, it breaks down like this:
- Step 1 tends to be very simple for HTH combat, potentially more complicated for Ranged combat if you're not in a dungeon corridor or small room, and simple to complicated for magic spells (depending on the spell in question.
- Steps 2 and 3 are actually combined by the Armor Class system, a bit of elegance that is sometimes misrepresented when the DM is describing what happens -- they sometimes equate the failed attack to a miss, when it could be a failure to penetrate armor. This was addressed by some added complexity of splitting up the AC bonuses for agility vs. armor on the character sheet in later versions of the rules.
- Step 4 is, of course, the damage roll.
Compare this to something like HERO, where:
- Step 1 is simple to moderate difficulty (especially if you're dealing with special senses, special ranged powers, and mental abilities)
- Step 2 is the attack roll and determines whether or not the target was hit (and optionally, where the target was hit)
- Step 3 and 4 are "combined" in that the damage is rolled and is modified (usually reduced) by various types of defenses, before they're applied to the target.
Why bring this up? It's because I used to disparage the so-called "abstract Armor Class" system, but having come back to it -- I realize that it also contributes to streamlining of combat. It can perhaps be further tweaked (as was done in a somewhat confusing manner in AD&D and later in 3rd Edition), but it is a powerful tool in simplifying combat rounds.