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Why Do Computers Use So Much Energy?

blogs.scientificamerican.com

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Re: Why Do Computers Use So Much Energy?

#81

Post by DenisM »

While the article deals with theoretical limits, there are some practical limits. As they are already coming up in other comments might as well list them out:

[...] There are several factors contributing to the CPU power consumption; they include dynamic power consumption, short-circuit power consumption, and power loss due to transistor leakage currents: [...]

[1] https://en.wikipedia.org/wiki/CPU_power_dissipation

[2] https://physics.stackexchange.com/questions/34766/how-does-p...

Re: Why Do Computers Use So Much Energy?

#82

Post by krylon »

mikeash wrote: post #76
lucideer wrote: post #12

> Precise estimates vary, but currently about 5 percent of all energy consumption in the U.S. goes just to running computers 30% goes on transport. > the human brain is a computer. This particular computer uses some 10–20 percent of all the calories that a human consumes So society's computer uses 5 percent and our own, evolved over millions of years, uses up to 20. I'm not saying computers can't or shouldn't be made…

It would make more sense to compare absolute numbers. A brain uses about 20W. A modern computer has similar consumption, but is many orders of magnitude less powerful.

Well, evolution has spent millennia optimizing human brains, and millions of years optimizing brains in general, while we have been building computers for ~70 years, about a human lifetime.

And for much of those 70 years, energy efficiency was not the top priority.

Re: Why Do Computers Use So Much Energy?

#83

Post by kerbalspacepro »

mikeash wrote: post #76
lucideer wrote: post #12

> Precise estimates vary, but currently about 5 percent of all energy consumption in the U.S. goes just to running computers 30% goes on transport. > the human brain is a computer. This particular computer uses some 10–20 percent of all the calories that a human consumes So society's computer uses 5 percent and our own, evolved over millions of years, uses up to 20. I'm not saying computers can't or shouldn't be made…

It would make more sense to compare absolute numbers. A brain uses about 20W. A modern computer has similar consumption, but is many orders of magnitude less powerful.

I'm not sure "powerful" is the word you're looking for. It's order of magnitude less _general_.

Re: Why Do Computers Use So Much Energy?

#84

Post by JoeAltmaier »

krylon wrote: post #82
mikeash wrote: post #76

Earlier quoted context omitted.

It would make more sense to compare absolute numbers. A brain uses about 20W. A modern computer has similar consumption, but is many orders of magnitude less powerful.

Well, evolution has spent millennia optimizing human brains, and millions of years optimizing brains in general, while we have been building computers for ~70 years, about a human lifetime. And for much of those 70 years, energy efficiency was not the top priority.

Yeah but biology never really had any choice about technology - it was always going to be cells and salts. Its really not about optimization - its about how lucky we are that real intelligence (if that's what we have) can even be achieved using cells and salts.

Re: Why Do Computers Use So Much Energy?

#85

Post by bunderbunder »

flyGuyOnTheSly wrote: post #65
old-gregg wrote: post #61

Earlier quoted context omitted.

Your laptop consumes 200w? Maybe I'm not reading this right, but I have a modern 3.5Ghz/8-core server in the closet which runs a small army of VMs and its from-the-wall draw never exceeds 80w (about 35w on idle).

My laptop is far from modern. It also has to power an old screen.

Wild guess - the disconnect here is that you're interpreting the maximum power rating of your laptop's power supply as an indication of what it typically draws.

It's more an indication of what your laptop would draw if it were doing GPU-accelerated deep neural net training while recharging a completely drained battery, plus a healthy margin of error just to be on the safe side.

Re: Why Do Computers Use So Much Energy?

#86

Post by platz »

because CPUs are the least efficient computing device, precisely because they are so general.

The future of hardware will be reprogrammable circuits that specialize to repeatable tasks

ICFP 2018 Keynote Address: The Role of Functional Programming and DSLs in Hardware https://www.youtube.com/watch?v=VqYkcGRr8x0

Re: Why Do Computers Use So Much Energy?

#87

Post by bunderbunder »

AcerbicZero wrote: post #60

Because energy is cheap, and optimizing for efficiency would be a waste of time/money (currently).

Energy is cheap if you're operating a desktop computer that's plugged into the wall.

If you're operating off of a battery, which accounts for a huge amount of consumer computing (especially if phones count), then it starts to matter a lot. Which is why consumer devices tend to be so heavily optimized for efficiency.

If you're operating a datacenter, it also quickly becomes a big part of your costs. Which hasn't necessarily been an immediately pressing concern for Intel, sure, but that may be why companies like Google have been toying with ditching Intel for ARM.

Re: Why Do Computers Use So Much Energy?

#88

Post by cfallin »

simias wrote: post #45
lucideer wrote: post #12

> Precise estimates vary, but currently about 5 percent of all energy consumption in the U.S. goes just to running computers 30% goes on transport. > the human brain is a computer. This particular computer uses some 10–20 percent of all the calories that a human consumes So society's computer uses 5 percent and our own, evolved over millions of years, uses up to 20. I'm not saying computers can't or shouldn't be made…

>So society's computer uses 5 percent and our own, evolved over millions of years, uses up to 20. This comparison doesn't make a lot of sense to me. It's not even comparing apples to oranges, it's comparing apples to the concept of taste. Furthermore these percentages don't really tell you much regarding efficiency, I'm sure there are less developed societies where computers count for less than 5% of all energy consu…

Why not, though? Energy is energy -- we (humans) oxidize food, basically burning it slowly, to power our bodies. Whether the energy is carried by glucose/ATP or electric current is just an implementation detail.

Comparisons are frequently made in other domains as well -- e.g., cyclists measure power outputs in watts.

The rule of thumb I've understood is that the brain runs on about 20 watts (peak power), and a human on average runs on about 100 watts. That's 8.64 MJ/day, which converts to 2064 food calories (kcal), at 4184 J/kcal.

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