SV: Capacity of the brain

Robert Herndon rmhj at
Thu Sep 2 17:34:46 EST 1999

In comp.arch Russell Wallace <manorsof at> 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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