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I have read in an article that newer CPU cores have narrower circuit tracks so more transistors can fit in the core. The author wrote that since there are more transistors, the voltage is reduced.

"As the track width is reduced, more transistors can be placed within the same area, and hence the voltage can be reduced."

How come newer processors tend to be consuming less power when in fact, the number of transistors they hold doubles each year as suggested by Moore's Law?

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More switching + less heat = more speed + less power. Wikipedia: MOSFET. –  Sampo Sarrala Jun 11 '12 at 12:28

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Either the author wrote something untrue, or your understanding is wrong.

Chips (including CPU's) are build with smaller parts. This has a few results.

  1. Parts are smaller. So on the same space you can add more parts.
  2. Smaller and shorter paths on the chips means the chips can run on a lower voltage.
  3. Heat density increases.

The first point should be obvious. With smaller parts you either build a smaller (and cheaper) chip. Or you build a chip which can do more things. (E.g. more cores, more cache etc).

Point 2 is best explained by using an example with pipes

Imagine a system with pipes, valves and water. If I open a valve to allow water into an empty pipe it takes some time before the water arrives at the end of the pipe and builds up some pressure. The bigger the pipe, the more water I need to add to the pipe to get the same pressure. The longer the pipe the longer it takes for water to arrive at the other end. Smaller and shorter pipes will be more efficient.

Now replace the water with electrons and the water pressure with voltage.

With shorter paths on the chip you can do with lower voltage. With smaller paths you need less electrons and the chip uses less power. It also allows signals to arrive faster and thus allows higher number of changes in pressure on and pressure off. (Read: More MHz).

As a result there is a corrolation between more parts on a chip and lower voltage needed by the chip. But one does not cause the other. Corrolation is not causation.



As to why newer processors tend to be consuming less power when in fact, the number of transistors they hold doubles each year: This is due to a few things. E.g:

  1. Faster chips tend to sell. More components allows for more cores, more cache. You could build a chip as fast as the previous generation, and let it use less power. Or you can build a faster chip. People buy faster chips, even if they do not need the speed. So faster chips get designed.
  2. More tasks get moved to a CPU. In the old days you had the CPU, the external cache and a few (2 or 3) chips. All of these used power. The second level cache got moved onto the CPU. The memory coltroller got moved onto the CPU, GPU's get moved to the CPU, external communication (e.g. PCIe lanes) hget moved to the CPU. More parts means more power needed for the new massive CPUs. But less power than a old style CPU and all the other external chips.
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Not only can run on lower voltages, but have to run on lower voltages as the insulating layers keep getting thinner... –  Brian Knoblauch Jun 11 '12 at 13:30
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Nods. I could add more information, explaining leakage, heat density, heat increase on speed increase etc. But I was afraid to make a confusing jumble while trying to andswer more than was asked for. –  Hennes Jun 11 '12 at 14:37

You're concentrating on the wrong metric. It's not more transistors that leads to less voltage. It's the "narrower tracks" which is called die size. The smaller the die size, the less drop in voltage from one connection to the next. Therefore a lower voltage can be used to the same effect.

The fact that the manufacturers can fit more transistors in the same space because the die size is smaller is another effect of the shrinking die size. But dropping the voltage drops the power dissipation more than increasing the transistor count increases the power dissipation. Thus leading to a net reduction in power consumption.

These guys explain it a bit better and in more detail than I can:

http://www.tomshardware.com/forum/293657-33-smaller-size-heat-production

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