SV: Capacity of the brain
rmhj at rmi.net
Thu Sep 2 17:34:46 EST 1999
In comp.arch Russell Wallace <manorsof at iol.ie> wrote:
> Lawrence Woods wrote:
>> I recall an old Reader's Digest space-filler from my youth (late 50's or
>> early 60's) that claimed a computer with the capacity of the human brain
>> would occupy a building the size of the Rockefeller Center in New York,
>> and require the entire East River to cool it.
>> I wonder how big that Rockefeller Center computer would be using
>> today's technology. Any ideas?
> They were being excessively optimistic; back in those days, the
> complexity of the brain wasn't fully appreciated.
> In round numbers (assuming our current understanding of how neurons work
> is more or less correct), here are the raw figures for the human brain:
> Storage capacity: 10^15 bytes
> Processing speed: 10^18 calculations per second
The original quote (from memory) is attributed to Vannevar Bush, and
involved the Empire State Building and 3 Niagaras to cool it.
The empire state building has a volume of about 37 million cubic feet.
Assuming an acorn tube or similar requires 5ml volume (err on the small
side), that yields about 1.05*10^12 gates, neglecting power cables and
supplies, coolant channels, pumps, etc..
Top-end processors these days seem to run 10-20 * 10^6 transistors,
so 50-100k CPUs should cover it. If you want to include memory
chips, you can divide by up to another 10 or so (DRAMs have lots of
As Lawrence Wood wrote, a lot of the complexity of the brain was
underestimated. For many years, and still often today, claims are
made that the human brain has about 10^10 neurons. To paraphrase
a joke among doctors: Yes, the brain has about 10^10 neurons.
And 10^11 of them are in the cerebellum. (A section of the brain
near the brain stem that deals with coordination.)
I would presume that Vannevar Bush was familiar with the idea that
the brain had about 10^10 neurons, and was presuming equivalence
between neurons and tubes/gates. This isn't a fair comparison,
however, as neurons often have up to ~1000 connections, and
these connections are neither simple, symmetric or equivalent to
each other, nor immutably fixed in character.
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