Unity3D's Entity Component System (ECS) architecture represents a significant shift from traditional object-oriented game development approaches. This architecture separates game objects into three distinct elements: entities, components, and systems.

Entities serve as simple identifiers without inherent behavior or data:

public struct GameEntity
{
    public uint identifier;
}

Components contain the actual data and functionality:

public struct TransformData : IComponentData
{
    public float3 position;
    public quaternion rotation;
}

public class PhysicsComponent : MonoBehaviour, IConvertGameObjectToEntity
{
    public float mass;
    public void Convert(Entity entity, EntityManager manager, GameObjectConversionSystem conversionSystem)
    {
        manager.AddComponentData(entity, new PhysicsProperties { massValue = mass });
    }
}

Systems process components and implement game logic:

public class MovementSystem : SystemBase
{
    protected override void OnUpdate()
    {
        float timeStep = Time.DeltaTime;
        Entities.ForEach((ref TransformData transform, in VelocityData velocity) =>
        {
            transform.position += velocity.direction * velocity.speed * timeStep;
        }).ScheduleParallel();
    }
}

The EntityManager handles entity lifecycle and component management:

public class SceneController : MonoBehaviour
{
    private EntityManager entityController;
    
    private void Initialize()
    {
        entityController = World.DefaultGameObjectInjectionWorld.EntityManager;
        Entity newEntity = entityController.CreateEntity(
            typeof(TransformData), 
            typeof(VelocityData));
            
        entityController.SetComponentData(newEntity, new TransformData { position = float3.zero });
        entityController.SetComponentData(newEntity, new VelocityData { speed = 2.5f });
    }
}

To implement a basic moving object:

1. Create an empty GameObject with a SceneController script
2. Add a cube with Physics components
3. Attach a conversion component to link to ECS
4. The system will automatical process movement each frame