I came across an interesting little review in The Inquirer recently describing the Themis Slice, a three-socket Opteron-based machine said to be more resilient, to improve power and cooling functions and to offer a performance boost to boot, compared to four-socket designs.
Most of you are probably wondering how a three-socket machine can out-class a four-socket machine. The trick lies in the connectivity between the sockets. In a four-socket approach, related data might have to hop over one processor to tie into another. With a three-socket design, all sockets are connected directly, so latency is improved.
Granted, this probably won't be noticeable in most workloads, but the higher the cluster, the more the latency factor may come into play.
The Slice also features two PCIe slots and two InfiniBand 4x ports, and they've also figured out a way to fire up 16GB of RAM with only six DDR400 slots.
To be frank, it's not entirely clear exactly what sort of role this thing could play in a typical enterprise. My guess is that the company probably has some sort of specialty applications in mind.
Anyway, you can delve into the details here.