Looking at the picture below you can see what Calxeda's ARM based server node will look like, an add-in card which requires two PCIe 2.0 slots to communicate with the mainboard. On the node are four Cortex A9 CPUs, each with two PCI-Express 2.0 controllers, a DDR3 memory controller, and a SATA 2.0 disk controller, as well as an integrated Layer 2 distributed fabric switch for ethernet connectivity. The mainboard these are connected to does very little, this server will depend on ethernet for its interconnect for now but it is likely that they will find something else to use though they may end up needing to license from AMD or Intel.
The Register took a look at the comparative benchmarks which came with this release, an Intel Xeon E3-1240 with one Ethernet port and 16GB of DDR3 which should be roughly equivalent to the new HP Redstone servers. They had some questions about the methodology used for the power usage on the Intel system as it was not describing the most power efficient usage of the Intel system and perhaps was not representative of the Intel system they actually benchmarked at all. Check out the benchmark as well as Calxeda's response in the full article.
"Calxeda, the ARM server-chip upstart that HP tapped for its "Redstone" hyperscale servers last November, is getting ready to ramp up production on the server cards that use its quad-core EnergyCore ARM processors, and is making waves with benchmarks while promising to do a better job with comparative testing against x86 architectures."
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