Yeah they do these for experimental purpuses, they got rid of the powermacs soon after they first built the system. they will also probably get rid of these soon.
I don't think they will be geting rid, of these anytime soon.
They have room for expansion now and with they way their cluster is set up they can add more, or upgrade a few at a time and it won't hurt they. The nodes don't all need to be identical in processor speed.
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