Advanced Micro Devices Inc (AMD)

[chipguy]

4P Opteron has the average diameter 1.17 hops
8P Opteron has the average diameter 1.64 hops

So the memory access latency is 121 ns for 4P system and 137 ns for 8P Opteron system.

You still don't get it do you? The average number of hops is meaningless, it is the maximum
number of hops in any system that is important. The Opteron relies on a broadcast coherency
system. That means any processor that wants to read memory has to broadcast its intent to
every other processor in the system and then wait to see if one of them has the target line
cached. Hop, hop, hop, hop.