unity-ecs-dots

Unity ECS / DOTS (Data-Oriented Technology Stack)

Based on Unity 6.3 LTS (6000.3) -- Entities 1.3, Burst 1.8, Jobs package

Core Concepts

ECS (Entity Component System) is Unity's data-oriented framework. It replaces the GameObject/MonoBehaviour model with a cache-friendly, high-performance architecture.

ECS vs MonoBehaviour

Aspect	MonoBehaviour	ECS
Identity	GameObject (heavy, managed)	Entity (lightweight int ID)
Data	Class fields on components	Unmanaged structs (IComponentData)
Logic	Methods on MonoBehaviour	Systems (ISystem / SystemBase)
Memory layout	Scattered across heap	Contiguous chunks by archetype
Threading	Main thread only	Jobs + Burst for parallel work

Entities

Entities are lightweight identifiers (an index + version integer). They have no behavior and no data -- they are handles used to associate components.

Components (IComponentData)

Components are unmanaged structs with no methods. They hold only data.

using Unity.Entities;

public struct Speed : IComponentData
{
    public float Value;
}

public struct Health : IComponentData
{
    public float Current;
    public float Max;
}

Archetypes and Chunks

An archetype is a unique combination of component types. All entities with the same set of components share an archetype. Entities are stored in chunks (16 KB blocks) grouped by archetype, enabling cache-efficient iteration.

World and EntityManager

A World contains an EntityManager and a set of systems. The default world is created automatically. EntityManager is the primary API for creating/destroying entities and adding/removing components.

Baking and SubScene Workflow

Baking converts authoring GameObjects into runtime entities. This is a one-way conversion that happens at build time or when a SubScene is loaded in the Editor.

Baker

using Unity.Entities;

// Authoring component (MonoBehaviour on GameObject)
public class SpeedAuthoring : MonoBehaviour
{
    public float speed;
}

// Baker converts authoring data to ECS components
public class SpeedBaker : Baker<SpeedAuthoring>
{
    public override void Bake(SpeedAuthoring authoring)
    {
        var entity = GetEntity(TransformUsageFlags.Dynamic);
        AddComponent(entity, new Speed { Value = authoring.speed });
    }
}