What's the difference of X.org and XFree86

[yeweikeke-maillist at yahoo.com]

 Hi,
   I'm using FBSD 4.10. I want to know what's the
 difference of X.org and XFree86. 
   I'm using XFCE4, can it run on X.org?
 
   Can someone supply some url for reading the
 difference?
 Thanks.


=====
Regards,
Ye Wei

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