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Comment by geuis | Hacker News Reader

Super long story short (literally, the first question doesn't get answer for something like 1000 words later):

What is dark silicon?

"Dark silicon is the fraction of chip that needs to be powered off at all times due to power constraints."

Long and short is that because of a combo of energy use and heat dissipation at the scale of upcoming transistors, maybe upwards of 50% of the transistors on a chip may need to be off. This then begs the question, why continue developing smaller scales of transistors if the technology can't be utilized because of heat and power needs.

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Even if you can't power every transistor simultaneously, shrinking allows you to layer on a whole bunch of specialized logic blocks. They're dark almost all the time, and when they're lit up they're displacing much more energy intensive general purpose computation.

Things like hashing/encryption functions, hardware encoders and decoders, even full blown FPGAs are all candidates.

You can also make more, slower cores, running at lower voltage, if you've got any embarrassingly parallel problems to work on.

It's not as attractive as just getting faster and more energy efficient across the board like we have been doing, but there's still room to move there.

Specialization is one of the ways forward mentioned in the article. But the ROI in this approach is much lower, and, as the article says, it could not justify the big investments that are required to create a new process.

>it could not justify the big investments that are required to create a new process.

Not yet, perhaps. New processes are effectively guaranteed to be needed at some point though.

Smaller transistors require lower voltage, and heat generated is related to the square of the voltage at a given size. So it's still useful to try to shrink the fab process.

However fab process shrink is a very expensive endeavor and the article argues that: "We may stop scaling not because of the physical limitations, but because of the economics."

So while for awhile now we knew we were going to hit the physical limitation of silicon at some point, the reality might actually be even worse because due to dark silicon and the economical constraints it imposes, there may not be enough incentive to keep shrinking.

To be fair to silicon, the human brain is very similar. It's never 100% active but at one time or another it all gets used.

To be fair, we have absolutely no idea how the human brain functions, and whether the analogy with silicon is relevant at all... Some have posited that consciousness is a function of a wave-like property of the entire brain, for example. That may be a load of bollocks, but the reality remains that we don't know much about how the brain does its magic.

We don't know how it works in detail but we can see which parts of the brain are doing stuff at any given time, and we've had a lot of progress associating different functions with different areas of the brain. http://en.wikipedia.org/wiki/Functional_magnetic_resonance_i...

No, we can detect changes in blood flow, and we've posited that there's a correlation between this blood flow and brain activity, and found that that is consistent with the way the blood flows alter.

This does not in any way rule out that the parts of the brain that are not showing up in the fMRI are participating in the thinking process at that moment. We have no idea whatsoever of how the thinking process itself unfolds.

That is not a good description of the concept of dark silicon. A better description would be, we cannot power all transistors at the same time because there is a power limit with regards to how much power a chip can consume.

Just because you may only be able to power x% of your chip, doesn't mean x% of your chip is useless. Some times you need to turn off parts of the chips anyways. Examples include cache misses or particular hardware flows. Other times you can decrease frequency due to program characteristics. For everything else we throttle because we cant power all the transistors at all times.

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