Eclipse has different folders for each size (xxhdpi, xhdpi, hdpi ...)
They are also in Android Studio. The Android Tools team hid them.
If you look just above the project explorer tree on the left, you'll see a drop-down list that probably says βAndroidβ right now:

This is an Android project view that gives you a somewhat synthetic look at your project, folding things like resource sets and sources to hide these details.
Eclipse users are likely to be happier with the classic look of the project that you get by clicking this drop-down list and switching it to βProjectβ:

This works just like the Eclipse Package Explorer, where you get the actual file system view of what is happening, complete with resource set directories.
All this applies to the file system, but the Android project view masks it a bit.
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