From www.anandtech.com :
By far the most interesting thing about the CPUs from a physical standpoint is their pincount. The ClawHammer has 754 pins (up from 462 on the Athlon and even up from 603 on the Xeon) and the Sledgehammer has a whopping 940 pins which is just over twice as many as the current generation Athlon.
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The AMD reference board goes by the name Solo, and is a pretty standard ATX motherboard. There is a single 754-pin Socket on the board for a ClawHammer CPU and it introduces what will most likely become the new (or something very similar to it) retention mechanism for AMD's Hammer line of CPUs.