Angular provides several change detection strategies to optimize the performance of change detection. However, the default strategy is named Detection. During this process, Angular walks the entire tree of components from the root to the children components. Each time the tree changes, Angular notifies the components by calling their _detectChanges method. For components that use the OnPush change detection strategy, Angular doesn’t walk the entire tree each time. Rather, it compares the current and previous values of data properties and calls the _detectChanges method only when a change occurs. By default, Angular uses the strategy that walks the entire tree.