# SubsystemRegistration

> Callback invoked when starting up the runtime. Called before the first scene is loaded.

## Definition

* **Type:** Field
* **Namespace:** [UnityEngine](/engine/6000.0/script-reference/unityengine.md)
* **Assembly:** UnityEngine.CoreModule

```csharp
SubsystemRegistration = 4
```

### Remarks

For more info on ordering see [RuntimeInitializeOnLoadMethodAttribute](/engine/6000.0/script-reference/unityengine/runtimeinitializeonloadmethodattribute.md).