Server
Roblox games are multiplayer by default and run in a client-server model. The Roblox server is the ultimate authority for maintaining the game's state, and is responsible for keeping all connected clients in sync with the server.
Client
When a game runs, Roblox copies a version of the "edit" data model that you built and published from Studio and runs it on Roblox servers as the "runtime" data model.
Connected clients also receive a copy of the runtime data model and any initialization of the player occurs, such as initializing a player's backpack (inventory) or local user interface. When a game has Workspace.StreamingEnabled set to true, the server initially only sends a subset of content under Workspace that is closest to the client. The client then renders the 3D world and begins running any applicable scripts.
Replication
The server constantly updates connected clients, keeping everything in sync across the server and clients through a process called replication, which synchronizes the data model, physics simulation, and chat messages. Replication logic exists on both the client and server to ensure synchronization.
Data model changes can occur in a variety of cases, such as when something in the 3D world is created or a property of the 3D world changes. This typically occurs when a script on the server or client makes a change that needs to be reflected on the other side of the client-server boundary. The following diagrams show common scenarios for data replication.
Most players on Roblox game between 100–300 milliseconds of network latency. Roblox Studio playtesting runs with a default of no latency, but you can change Network Simulation settings in the Network section of Studio Settings (AltS on Windows; ⌥S on Mac). Use a minimum delay of 50–150 milliseconds in both the inbound and outbound directions to better simulate how network latency will affect your game.