Computing systems vary across many dimensions

Part 4 of Is “Is the brain a computer?” even a good question?

It’s too late to change the answer to “Is the brain a computer?”, and it distracts from the really useful questions about the relations between computers and brains. Nevertheless, a deeper look finds that brains stretch the definition of computing, perhaps beyond the breaking point.

This is part 4 of a series of brief essays (sometimes very brief) on aspects of this question. Part 1 contains the introduction and an index to the whole series.

Computing systems vary across many dimensions

If you look at the wide variety of conventional computers, unconventional computers, and at brains, you can end up with five different dimensions, shown in the chart below. Yet all the different combinations of characteristics on each dimension are universal [with a footnote], and each can emulate any of the others. Where they differ is in the contingencies of their evolutionary and historical lineages, which sometimes had powerful performance consequences in certain environmental or economic contexts, and sometimes led to divergences with no obvious advantages.

When you look specifically at good old fashioned von Neumann computers and at brains, it’s not unreasonable to conclude that they’re about as far apart architecturally as it’s possible to get, as seen in the next chart. On every dimension of variation, computers and brains are at opposite ends of the spectrum.

[Footnote: Noise-free analog computers can execute infinite-precision operations in constant time, and are thus more powerful than alternatives. But in real life there’s always noise, so this is not a practical issue.]

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