[Network gaming 1] The Horror of Lockstep: The Illusion of Physics Synchronization and the Brutal History of Multiplayer

For people around my age (born in '85), StarCraft is practically treated as a national folk game. The game was born in the US, but I remember completely humiliating some American acquaintances who claimed they were "good at StarCraft" by playing them with a two-worker handicap. Mind you, I was still the weakest player in public Korean lobbies. I'm not here to brag about my StarCraft skills. The point is, by looking at this Korean national pastime, you can trace the evolutionary history of network gaming.

Anyone who played StarCraft has seen opponents trigger a 'disconnect' and run away when they were losing. This is actually one of the fundamental frustrations of network play. It showcases the limitations of a technique commonly known as Lockstep.

1. What is Lockstep?

Back in 1998, when StarCraft was released, using a dedicated internet line was a rarity. In South Korea, the internet evolved alongside StarCraft, right around the time when cable-based dedicated lines like Hanaro Telecom and Thrunet were just starting to roll out. Before that, networks were capped at 56kbps dial-up modems. Dedicated cable lines meant the internet was always on, and you wouldn't get smacked in the back of the head by your mom for racking up phone bills at 30 won per minute. (Speaking from personal experience, of course.)

The reason this ties into Lockstep is that back then, there was absolutely zero know-how or infrastructure for real-time network communication. This applied even to Blizzard, a company with practically alien-tier development skills at the time. Wanting to implement network play for StarCraft, they came up with a highly idealistic concept:

"Let all clients exchange only their identical inputs, and run the exact same simulation on each device to match the outcomes."

For saving traffic on a sluggish 56kbps dial-up modem (which, by the way, is about 53 times slower than the throttled 3Mbps you get when you run out of smartphone data), it seemed like the most perfect solution.

But by today's standards, this is absolutely absurd. Even now, with high-speed internet like gigabit fiber and 5G everywhere, connection drops are incredibly common. Let alone dial-up, where the connection would completely shut down if your mom simply picked up the phone in the living room. Applying such an idealistic methodology to such an unstable environment was doomed to fail.

Because the network of all syncing users has to mesh perfectly like gears, if even one person's ping spikes or connection wavers, everyone's screen freezes. This is exactly what causes that infamous "Waiting for player..." screen when someone rage-quits. Horrifyingly, this phenomenon is still happening in 2026, even after the Remaster. The Remaster only overhauled the superficial graphics; the underlying system remains exactly the same.

2. Thank God It Was 2D: The Curse of Floating-Point

The only reason StarCraft 1 could even function on Lockstep was that it used 2D tile-based fixed-point math.

With integer-based calculations, there is no chance for calculation results to deviate between clients. However, as eras shifted, games moved into 3D, and 'floating-point' math was introduced to calculations, making Lockstep a technology that should no longer exist. In games, 3D floating-point coordinates don't just stop at one decimal place like 55.1; they go down more than 10 decimal places.

Assuming that all players in the game can simulate this with perfectly identical synchronization is practically impossible. CPU manufacturers only adhere to the x86 spec. Even if you calculate the exact same formula, the final decimal digits produced by an Intel CPU and an AMD CPU will differ. The results will even minutely distort based on compiler optimization options or microscopic differences in frame rates (FPS). Ultimately, Lockstep creates parallel universes (Desync) where completely different outcomes occur on each person's computer.

3. The Ticking Time Bomb Called Physics Engines

Throw a modern 3D engine's 'physics engine' (like PhysX in Unity or Unreal) into the mix, and things go completely insane. Going too deep would be TMI, but physics engines are inherently non-deterministic.

Simply put, it's like a gacha system. Just as opening 100 loot boxes doesn't guarantee an SSR drop, throwing the exact same ball with the exact same force might make it bounce left off a rock on my computer, but bounce right on my opponent's computer. In a 3D environment where results vary from client to client, the naive Lockstep ideology of "just sync the inputs and the results will naturally match" could no longer function.

4. The Failure of Democracy and the Descent of the Dictator (Dedicated Server)

Eventually, the era arrived where client calculation results could no longer be trusted. Unable to tolerate clients arguing amongst themselves over "My character is alive!" vs. "No, you're dead!", system architects finally took drastic measures.

"Stop trying to reach a consensus among yourselves (Lockstep). All your client calculations are Fake."

They established a single dictator that monopolizes all rulings—the Single Source of Truth, the 'Dedicated Server'. Users now entered an era where they must offer their inputs to the server, and blindly receive only the 'results' of the physics and coordinates calculated by the server.

And the establishment of this centralized control architecture became the fundamental foundation that gave birth to the MMORPG genre, where thousands of people gather in a single world.