Future microprocessors and off-chip SOP interconnect

Limits to chip power, dissipation and power density and limits on the benefits of hyperpipelining in microprocessors threaten to stop the exponential performance growth in microprocessor performance that we have grown accustomed to. Multicore processors can continue to provide historical performance growth on most modern consumer and business applications. However, power efficiency of these cores must also be improved to stay within reasonable power budgets. This can be achieved by simplifying the processor core architecture, and reversing the trend toward ever more-complex and less power-efficient cores. To maintain overall performance growth with stunted per-core and per-thread performance, growth rates will require an even more rapid increase in the number of cores per die. Growing performance by increasing the number of cores on a die at this rate, however, puts unprecedented requirements on the corresponding growth of off-chip bandwidth. We argue that contrary to the International Roadmap for Semiconductors (ITRS) predictions, off-chip signaling frequencies are likely to exceed the frequencies of processor cores in the not too distant future, consistent with the system-on-package (SOP) concept in the first paper of this issue. If this approach is followed, a 1-TFlops multiprocessor die with 1 TB/s of off-chip bandwidth is feasible at reasonable cost before the end of the decade.