what is the difference between "/usr/bin/X" and "/usr/bin/Xorg"?

[jiang lei <john.jianglei@gmail.com>]

hi all:
  
    is there any difference between "/usr/bin/X" and "/usr/bin/Xorg"? On my debian box, /usr/bin/X is not symlink to /usr/bin/Xorg, and i can start X server with /usr/bin/X but fail with /usr/bin/Xorg? i google it but find nothing, could any one here help me? thanks in advance.