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Using the Mac OS 10.6 X11 client, XWindows is working, with small utilities like xcalc and xpbs, and with VMD 1.8.7. VMD performance seems sluggish, however. Note: when connecting with "ssh -X", starting VMD consistently leads to a crash of the X11 client. Connecting with "ssh -Y" (which disables X11 security protocols, for trusted connections) works instead. This problem has occurred with other computers in the past, and it's not clear whether this is a bug in VMD, the X11 installation on the cluster, or the Mac OS 10.6 X11 client.