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We are using multi core processors partially, because the waste heat of single core processors was to high to handle. (correct?)

Now we are using multi core processors that create less heat and need less energy although they have a much better performance than the old single core processors.

What is the reason? Why does the better multi core processor does not need produce more heat?

3 Answers 3

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Adding cores by itself doesn't decrease TDP. However, the development of multicore processors coincided with a transition to more efficient architectures. Furthermore, on multithreaded workloads, more cores at lower speeds will use less power than fewer, faster cores with the same performance.

The two classical metrics of CPU performance are IPC (instructions per cycle) and clock speed. While IPC is difficult to quantify due to dependence on the benchmark application's instruction mix, clock speed is a simple measurement yielding a single absolute number. Unsophisticated buyers would simply consider the processor with the highest clock speed to be the best product, and the Pentium 4 had the fastest clock speed.

  • The later Intel Core 2 and Core i processors are manufactured on more efficient semiconductor processes and use more efficient architectures that deliver better performance even at lower clock speeds, while consuming much less power and generating much less heat. See also: Why are newer generations of processors faster at the same clock speed?

  • Modern applications tend to use many separate threads and processes which can be run on separate processor cores. Especially in highly parallel applications, a quad-core processor operating at 2 GHz will often perform significantly better than a single-core processor operating at 5+ GHz, not least because the independent cores can each work on its own processor thread. On a single-core processor, context-switching overhead can significantly degrade performance with multiple tasks.

  • Furthermore, the power consumption of a processor increases dramatically as clock rates go up. Higher clock rates, especially when you go past 4 GHz, require large increases in processor core voltage VCORE. Heat dissipation increases with the square of VCORE, which means that extremely high clock speeds approaching 5 GHz and beyond are very difficult to attain and can significantly compromise the reliability of the processor. This itself means that for most workloads, a multicore processor will generate much less heat than a single-core processor for the same amount of performance.

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Processor design gets into solid EE fundamentals, but the technical reason why depends a lot on the processors you are talking about (you can't really equally compare the thermal output of a Intel 40386 to a Intel Core i7 same as you can't really equally compare the thermal output of a single core processor to a multi-core processor).

By all accounts, if something uses less energy, it will in effect, produce less heat (unless specifically built to do the opposite, like a space heater).

The biggest reason processors today are more efficient than their ancestors is simply scientific advancements have helped us understand how we can squeeze more efficiencies out of certain areas of a processor.

To wit, another reason why multi-core processors are better in today's computing world also has to do with time on processor. If I'm running a music player, while typing a word doc and surfing the web, each of those programs has to fight for a slice of processor time, which in effect means that my single core processor is working harder (context switches and what not), but if I had a 4-core processor, I could have each process running on it's own core (processor) and thus not have the complete extra workload that a single core might have.

TL;DR: the harder a processor has to work, the more heat it will generate, the more efficient it is at it's work though can translate to efficiencies in heat generation (i.e. a more efficient processor can generate less heat).

Hope that helps.

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No; multi-core processors were not adopted because they produce less heat. They were adopted because you can get more work done when you have multiple cores doing work at the same time. As a side effect of being able to get the work done faster, the processor can go back to sleep more, and in that state, it uses much less, or even zero power. Earlier processors, even when idle, used much more power, but a lot of work has gone into reducing the idle power consumption to zero or near there ( by switching all or most of it off ). The main reason though, for modern processors using much less power is simply that they use smaller transistors which require less energy to switch, and run at lower voltages, which again wastes less energy.

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