QuakeWorld: Carmack makes 300 ms dial-up multiplayer feel like single player

In August 1996 John Carmack copied the Quake codebase and began a project he called QuakeWorld: internet play as its own product, with separate client and server executables that would peacefully coexist with the registered game. His motivation was blunt - v1.01's netcode had been designed for connections under 200 ms, but at the time about 99% of the world reached the internet over slip or ppp modem links that delivered 300 ms or worse, often through overcrowded ISPs.

His first move was architectural: he scrapped the reliable-stream netcode, which he had retrofitted with an unreliable sideband until it became a mess, and rebuilt it with the unreliable datagram as the basic primitive. The server stopped being a 20 fps game loop and became a fileserver-style loop that handled each incoming packet on arrival - moving only that player forward in time and answering in under 4 ms instead of over 50 ms. Bandwidth estimation let a clogged dial-up link simply stop sending rather than let routers buffer latency into multi-second stalls.

The biggest change was client-side movement simulation: the client guessed the outcome of its own movement until the server's authoritative reply arrived, so even over a 200 ms+ link movement felt like a local single-player game. Around it Carmack sketched a master server, persistent accounts, a global frag ranking and a roughly $10 name registration, while noting honest limits: other players and projectiles still lagged, so you had to lead your shots. The predict-locally pattern he described became the template for hiding latency in online shooters.