Bamboo computer

[Jim Battle]

Ron Hudson wrote:

...
> If the desert island has vines you could make a rope computer, as 
> described in a
> Scientific American, I don't remember the issue.

It was an april fool's issue, I believe.  If memory serves, the island 
was called APRLFUL or something like that.  The article showed how, with 
clever arrangements pullies, toggles, springs and such, inverters and 
simple logic gates could be produced.  Entertaining enough.

The problem with that "computer" is that the logic gates have no gain.

Each gate has no power supply other than the mechanical power of the 
input signals (ropes getting pulled).  For instance, say you pull an 
input rope of a NAND gate one foot (OK, let's keep it metric) ten inches 
:-) and the output rope moves nine inches, so the gain is 0.9.  Put N of 
these gates in series and the output signal is (0.9**N) of the input 
signal.  After half a dozen gates, very little is left at the output. 
The rope gates had a gain much less than 0.9 -- probably 0.5.

It is the same reason why computers aren't built of of just diodes and 
resistors.  You can have a gate or two in series, but then the signal 
needs to be reconditioned before being applied to the next stage.