# ISystem

> Interface implemented by unmanaged component systems.

## Definition

* **Type:** Interface
* **Namespace:** [Unity.Entities](/engine/7000.0/script-reference/unity/entities.md)
* **Assembly:** UnityEngine.EntitiesModule

```csharp
public interface ISystem
```

## Methods

| Method                                                                           | Description                                                    |
| -------------------------------------------------------------------------------- | -------------------------------------------------------------- |
| [OnCreate](/engine/7000.0/script-reference/unity/entities/isystem/oncreate.md)   | Called when this system is created.                            |
| [OnDestroy](/engine/7000.0/script-reference/unity/entities/isystem/ondestroy.md) | Called when this system is destroyed.                          |
| [OnUpdate](/engine/7000.0/script-reference/unity/entities/isystem/onupdate.md)   | Implement `OnUpdate` to perform the major work of this system. |