Intel: 1,000-core processor possible | Processors | Macworld: Initial multicore chip architectures depended on a set of protocols that assures that each core has the same view of the system's memory, a technique called cache coherency.
As more cores are added to chips, this approach becomes problematic insofar that "the protocol overhead per core grows with the number of cores, leading to a 'coherency wall' beyond which the overhead exceeds the value of adding cores," the paper accompanying Mattson's talk noted.
Mattson has argued that a better approach would be to eliminate cache coherency and instead allow cores to pass messages among one another.