SpiNNaker, that's the name of the system, is based on a chip developed by Steve Furber, the father of ARM's 32-bit RISC processor. Every chip will contain 20 cores on a single die; one of them is designated as a "head" and the others run the "neuron simulation".
All cores are interconnected on the die itselft, and all processors (thousands in the final system) are interconnected through a "Globally Asynchronous Locally Synchronous" architecture. The simulated neurons can "fire" to any other neuron in about 1ms, which is practically the same of humans.
Obviously, Furber and his team are far from recreating the 90billion neurons topology of human brain; according to the well known Moore's law, in a couple of decades a full simulation would be possible but, meanwhile, better models of the brain could be studied and exploited.