In version 6.0.x of 4D, if you wanted your database to load and use a plug-in (such as 4D_Pack, 4D Write, etc.), the plug-in was required to be placed inside of a (Mac or Win)4DX folder that resided inside the same directory as your structure. Version 6.5 of 4D introduced the new concept of a "Universal 4DX" folder. A "Universal 4DX" folder is a (Mac or Win)4DX folder that resides inside the 4D folder which is inside your platform's active "system folder" (WinNT folder, Windows folder, or on the Mac, the System Folder:Preferences folder). Should you do an install from the version 6.5.x Product CD you will, by default, end up with a Universal 4DX folder.
The concept of the "Universal 4DX" folder is as simple as it is convenient. Now you can place all your plug-ins into it and subsequently all of your databases will be able to find and load the plug-in/s that it requires. In other words, it is no longer necessary to have a 4DX folder FOR each database WITH each database.