Ben Cantrick (mackys) wrote,
Ben Cantrick
mackys

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Multicore processors are here to stay, but memory is a bottleneck.


And that's the situation today. Memory is much slower than processors and has been an essential bottleneck for fifteen years. Recently CPU speeds have stalled as well, limited now by power dissipation problems. As transistors switch, small inefficiencies convert a tiny bit of VCC to heat. And even an idle transistor leaks microscopic amounts of current. Small losses multiplied by hundreds of millions of devices means very hot parts.

Ironically, vast numbers of the transistors on a modern processor do nothing most of the time. No more than a single line of the cache is active at any time, most of the logic to handle hundreds of different instructions stands idle till infrequently needed, and page translation units that manage gigabytes handle a single word at a time.

But those idle transistors do convert the power supply to waste heat. The "transistors are free" mantra is now stymied by power concerns. So limited memory speeds helped spawn hugely complex CPUs, but the resultant heat has curbed clock rates, formerly the biggest factor that gave us faster computers every year.


http://www.embedded.com/columns/technicalinsights/205918952;jsessionid=ZZOMOSZISIANQQSNDLOSKHSCJUNN2JVN?pgno=2
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