Its helpful to contrast Calxedas approach with that of its main x86-based competitor, SeaMicro. SeaMicro makes a complete, high-density server product based on Intels low-power Atom chips that is built on many of the principles described above. Aside from the choice of Atom over ARM, the main place that SeaMicros credit-card-sized dual-Atom server nodes differ from Calxedas EnergyCards is in the way that the latter handles disk and networking I/O.
As described above, the Calxeda system virtualizes Ethernet traffic so that the EnergyCards dont need physical Ethernet ports or cables in order to do networking. They do, however, need physical SATA cables for mass storage, so in a dense design youll have to thread SATA cables from each EnergyCard to each hard drive card. SeaMicro, in contrast, virtualizes both Ethernet and SATA interfaces, so that the custom fabric switch on each SeaMicro node carries both networking and storage traffic off of the card. By putting all the SATA drives in a separate physical unit and connecting it to the SeaMicro nodes via this virtual interface, SeaMicro systems save on power and cooling vs. Calxeda (again, the latter has physical SATA ports on each card for connecting physical drives). So thats one advantage that SeaMicro has.
One disadvantage that SeaMicro has is that it has to use off-the-shelf Atom chips. Because SeaMicro cant design its own custom SoC blocks and integrate them with Atom cores on the same die, the company uses a separate physical ASIC that resides on each SeaMicro card to do the storage and networking virtualization. This ASIC is the analog to the on-die fabric switch in Calxedas SoC.
Note that SeaMicros current server product is Atom-based, but the company has made clear that it wont necessarily restrict itself to Atom in the future. So Calxeda had better be on the lookout for some ARM-based competition from SeaMicro in the high-density cloud server arena.