ElI5: Our brain uses about 10W of power, when a computer can use 100W. With our brain doing significantly more than a computer, how is it so much more efficient?

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ElI5: Our brain uses about 10W of power, when a computer can use 100W. With our brain doing significantly more than a computer, how is it so much more efficient?

In: Technology
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“Efficient” is a bit of an odd word to use when talking about CPUs, seeing as their efficiency is basically 0% as they only produce heat. CPUs are steadily increasing their IPC while reducing their power-draw, so it is limited by current manufacturing and not necessarily tied with current-day power draw. Doing significantly more than a computer is also subjective, a CPU can do quite a lot simultaneously that we would never be able to do.

Your brain is nothing like a computer, architecture-wise. Computers use programs that are millions of simple instructions from a set of a couple hundred instructions. The brain is parallel, executing a few hundred instructions from a set of zillions of complex instructions you call “thoughts”.

>with out brain doing significantly more than a computer

Can your brain do millions of additions or multiplications per second?

Your brain is not doing all that much in terms of raw logic.

The real answer is that billions of years of evolution have optimized biological organisms for energy efficiency. But in a sense, that doesn’t really answer the question. *Why* are brains so energy efficient?

I suspect one of the main contributing factors to be the way the brain is structured: it’s very “sparse”, in a sense that, at any given point in time, everything not currently needed is “turned off”. You may have heard that only a small fraction of the brain is “in use” at any given time. What this means is that, in a sense, the brain is doing the minimal amount of work necessary – only updating state where it’s relevant to the task at hand.

Conversely, computers tend to be big and stupid and simple and full of logic gates that flip whether their results are needed or not. Modern CPUs have started selectively enabling and disabling parts of the hardware based on what’s currently needed, but it’s many orders of magnitude less sophisticated than what the brain is capable of doing.

Also, despite almost a hundred years of engineering, transistors are still very energy inefficient. They don’t just propagate state changes, they also waste a bunch of current in the process.