

Plan 28 - jgrahamc
http://blog.jgc.org/2010/09/plan-28.html

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acconrad
It makes you wonder if there would even be enough space on the surface of the
earth to replace Google's or Facebook's modern day servers with the equivalent
computing power of these analytics engines - my guess is no.

~~~
gjm11
According to the Wikipedia article on the Analytical Engine, some other chap
called Ludgate designed a streamlined version which could do a 20-digit
decimal multiply in about 6 seconds; its volume was about 230 litres. (He made
detailed plans but never actually built it.)

20 decimal places is about 64 bits. One design for a 64x64->128 multiplier is
described in <http://www.patentstorm.us/patents/5912832/description.html> and
takes about 33k gates to achieve a propagation delay of about 200 gates. I'm
not sure what propagation delays are like on modern CPUs; let's suppose it's
20ps per gate, so that a modern-silicon multiplier can do a 4ns multiply in
33k gates. How much space should we think of that as taking up? Not just the
volume of the gates themselves; we need some volume for circuit boards,
cooling, power supply, etc., etc., etc. A small modern PC might be a litre in
volume and contains maybe the equivalent of 200M gates (CPU, memory, whatever
else). So 33k gates corresponds to maybe 1/600 of a litre. So, in volume per
unit power, modern technology beats Ludgate's version of the analytical engine
by maybe a factor of (230 x 6) / (1/600 x 4x10^-9) or about 2x10^14.

(Don't take this too seriously; there are a lot of very dubious assumptions in
the above.)

Now, let's say Google has 10^5 machines occupying 1 litre each. The equivalent
in analytical engines would be 2x10^19 litres, or 2x10^16m^3.

The radius of the earth is about 6.4 x 10^6 m, so its surface area is 4 pi r^2
~= 5x10^14 m^2. About 1/3 of this is land, so let's say 2x10^14 m^2. So we'd
need to cover the land area of the earth 100m deep in analytical engines.

Dubious assumptions or not, I think I agree with your guess.

~~~
olalonde
Just made my guess before reading yours. Some of my assumptions are more
generous than yours, but the conclusion is the same: not enough land area on
earth.

------
olalonde
From Wikipedia:

The analytical engine, an important step in the history of computers, was the
design of a mechanical general-purpose computer by English mathematician
Charles Babbage.

