How much are needed to equal an i7 more or less?
How much would cost this multi Panda board server vs a single i7? cost/performance
And how many energy this multi PAnda spend vs a single i7 energy efficiency
Also how well i7 scales vs ARM, then 4 i7s vs 4 multi Panda Borads alike systems, with the intermediate steps.
When comparing to an i7, ARM clusters seem to be much more expensive, a bit less power efficient, and not much faster, if at all. I think you're underestimating the power of Sandy Bridge and Ivy Bridge i7s. Even AMD systems are likely more power, time, and cost efficient. Keep in mind that whenever you do cluster computing, for every computer you add you're wasting electricity on powering a whole separate system, you drastically lower latency (by communication, error checking, translation between gathering the data and interpreting it for use, timing everything properly, the relatively lengthy wires, etc), you spend more time setting it up, and the more systems you have there's a higher probability of failure. In other words, if you're looking to massively parallel something without going beyond 64 cores, you're wasting time, energy, effort, and money on a cluster. You can get up to 64 threads in 1 system with a SPARC T3 setup. Also, there are server motherboards that allow 4 AMD CPUs at a time. I'm not sure if they support socket G34 (I think that's the socket name) but if they do you can have up to 48 cores using 4 of AMD's 12-core Opterons. Those Opterons are overall a much much better value than the Intel competitor.
There are some 16-core opterons, so you can get 64 x86 cores in a box too.
Thread hijack: Bulldozer module edition :)
One BD module = two int cores, one shared fp core. So only for floats you can say it's not two cores - for integer math it is two cores.