From: J. Andrew Rogers (andrew@ceruleansystems.com)
Date: Mon Mar 08 2004 - 21:53:36 MST
On Mar 8, 2004, at 6:10 PM, Keith Henson wrote:
> Biologic brains are at least three orders of magnitude slower and
> still work. How are they doing it?
Because they can keep their processors fed with data. That's all
memory latency really measures, how many objects can be referenced per
second. A human brain typically references roughly three orders of
magnitude more objects per second than our fastest processors. For
large fine-grained data structures (like the brain), memory latency (or
if you prefer, object reference throughput) *is* the computational
limit, not IPC and clock speed.
People are not used to thinking of things this way, but memory latency
pretty much defines the computational limits of our universe. It isn't
as obvious as Instructions Per Second or the amount of memory you have,
but it is a lot more important if you have to confine yourself to
finite time horizons.
Study the consequences of finite information propagation speeds (of
which memory latency is an example) on computational theory. It is the
gravest restriction on intelligence that this universe appears to have.
Perhaps not insignificantly, it is the only computational parameter in
which the brain *clearly* is orders of magnitude superior to the
silicon we can manufacture today.
j. andrew rogers
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