I recently purchased the re-issue of the 1st edition AD&D core rule books. I realized in retrospect that I only thought I was playing AD&D back in the day. Really, I was playing a sort of mish-mash of D&D and AD&D. One of the things I'm struck by is the differences in the two combat systems. In D&D there's a combat round checklist, and everything happens in a specific order. In this respect, it's very much like playing a wargame like Panzer Blitz. I ended up writing a short MATLAB script for predicting the probability of various outcomes of differently armed and armored opponents. It doesn't take into account special abilities. I was hoping that it'd be easily modified for the AD&D game. Unfortunately, that hasn't proven to be the case due to some of the following differences in the combat systems.
Time: D&D combat rounds are 10 seconds long. AD&D rounds are 1 minute long which are further subdivided into ten 6 second segments.
Surprise: In D&D the DM rolls 1d6 for both sides. A 1 or 2 indicates that side is surprised. It's fairly easy for both sides to be surprised and spend a round doing effectively nothing, which, in practice, most of the time means that nobody is surprised since if both sides are surprised and do nothing, the DM just marks off a round on his time record and keeps the game moving. With AD&D, while both sides can be surprised, it's possible for one side be less surprised. The degree to which one side or the other is less surprised depends on the difference in their surprise die rolls. Additionally, if both sides are surprised equally, nobody is surprised, negating the effects of surprise entirely. Interestingly, in certain cases, extremely surprised parties can be surprised for multiple segments.
Initiative: In D&D, initiative is determined each round. In AD&D, achieving surprise is also equivalent to winning initiative, so it's only determined on rounds where nobody is surprised, or all sides are equally surprised. This means that surprise is more deadly. Not only is there a potential to get free attacks, but you might get multiple free attacks (in the event of both sides being surprised but there being a large difference in their surprise rolls), and on top of that, you get to attack first each segment after the surprise segments are resolved. YIKES! Additionally, initiative is determined at the beginning of the round, hence the advantage of intitiative is carried through all ten segments.
Surprise in D&D feels to me almost like an optional rule, inserted and often employed at the DM's discretion. In AD&D achieving surprise is an integral part of combat. Additionally the advantage of initiative is much more decisive.
Weapon Speed Factors: This one has me really perplexed. Most combats are not 1 on 1 encounters, hence they are not uniformly armed. I can't help but wonder if these rules were only meant to be employed in the event of a duel. It makes me think an early D&D player must have been an SCA wire-weenie.
I can't help but wonder if this would have the effect of making shrewd players very focussed on achieving surprise, since the advantages are so much greater. I'm not sure a fast weapon matters very much, though, since I can only see it mattering in one-on-one encounters.