two different "UnityEngine.UI.dll"-files

Hi

In the Unity-Installation-Folder are two different “UnityEngine.UI.dll”-Files.

C:.…\Editor\Data\UnityExtensions\Unity\GUISystem\UnityEngine.UI.dll
C:.…\Editor\Data\UnityExtensions\Unity\GUISystem\Standalone\UnityEngine.UI.dll

Whats the difference? Both files have also a different file size.

Greetings
Gargi

Judging by the paths I would assume there is slight differences in compatibility with Stanadalone and other platforms.