Me..Four systems running here and none are single socket.
Why? Here's some reasons:
1) Boards are better quality
2) Electrical usage for a given job done is better.
3) Space: The duals outperform the singles by a wide margin and take essentially the same space
4) Buy top boards,they don't break and I mean DON'T.
Whens the last time you saw a single socket board run 3+ years at 100% load with out a boot other than from a electrical outage or twice a year cleaning?
I see that all the time.
5) Time effectiveness: Toss any muti threaded task on a dualie and it's done much faster than any single socket machine can do.
Ok,thats settled, back on topic now.
Oh, I forgot one thing:
6) E-PEEN!

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