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Contents Background A Brief History of Microprocessors Moore's Law Past Efforts to Increase Efficiency The Need for Multicore Multicore Basics Multicore Implementations Intel and AMD Dual-Core Processors CELL Processor Tilera TILE64 Multicore Challenges Power and Temperature Cache Coherence Multithreading Open Issues Improved Memory System System Bus and Interconnection Networks Parallel Programming Starvation Homogeneous vs. Heterogeneous Cores Conclusion

Abstract

As personal computers have become more prevalent and more applications have been designed for them, the end-user has seen the need for a faster, more capable system to keep up. Speedup has been achieved by increasing clock speeds and, more recently, adding multiple processing cores to the same chip. Although chip speed has increased exponentially over the years, that time is ending and manufacturers have shifted toward multicore processing. However, by increasing the number of cores on a single chip challenges arise with memory and cache coherence as well as communication between the cores. Coherence protocols and interconnection networks have resolved some issues, but until programmers learn to write parallel applications, the full benefit and efficiency of multicore processors will not be attained.

Background

The trend of increasing a processor's speed to get a boost in performance is a way of the past. Multicore processors are the new direction manufacturers are focusing on. Using multiple cores on a single chip is advantageous in raw processing power, but nothing comes for free.

Source: New Scientist Blogs

With additional cores, power consumption and heat dissipation become a concern and must be simulated before layout to determine the best floorplan which distributes heat across the chip, while being careful not to form any hot spots. Distributed and shared caches on the chip must adhere to coherence protocols to make sure that when a core reads from memory it is reading the current piece of data and not a value that has been updated by a different core.

With multicore processors come issues that were previously unforeseen. How will multiple cores communicate? Should all cores be homogenous, or are highly specialized cores more efficient? And most importantly, will programmers be able to write multithreaded code that can run across multiple cores?

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