In reading through the D&D Rules Cyclopedia (1991) I came across this helpful summary of the differences between RC D&D and AD&D (p. 291):
· AD&D characters tend to have higher ability scores, especially if some of the optional character generation rules are used. However, ability score bonuses are generally gained at a score of 15 instead of 13.
· AD&D characters usually use different dice to roll hit points (for example, fighters roll d10).
· AD&D game clerics get spells at first level, and often start with two or three spells.
· The AD&D system separates character class and character race. Different class and race combinations are available (e.g. dwarf fighter/thief).
· The AD&D alignment system adds a Good-Evil axis to the D&D game Law-Chaos axis, allowing greater detail (Lawful-Good, Chaotic-Neutral, etc.).
· AD&D game spells are more complex. While one or two elements of a D&D spell may vary by character level, any and all elements of an AD&D spell (range, duration, effect) might vary in this way. AD&D spells are also more likely to have multiple effects or reversals.
· AD&D game magical items are more complex; many have three or more separate functions.
· The systems have different combat round time scales (affects encounter pacing).
· The AD&D system uses a 10-point armor class scale.
· The AD&D game weapons inflict different damage against larger-than-man-sized opponents than against smaller opponents.
· Equipment prices and encumbrance numbers are different between the two systems.
· Some D&D optional rules (Fighter Maneuvers, Weapon Mastery, and so on) have no equivalent in the AD&D system.
While I was aware of these differences, I thought it was nice to have the “official” listing as per TSR. It’s proven to be helpful as I work to determine which incarnation of (A)D&D I’ll ultimately choose as my main system.