On Tue, 17 Mar 1998, Bill Yakowenko wrote:
Doug Yowza <yowza(a)yowza.com> wrote:
] To be fair, analog computers can do things digital computers can't. For
] example, a digital computer can only approximate 1.0/3.0 whereas an
] analog box has no trouble with this. Certain ops would also be much
Actually, you've got that backwards. Contained in your message above
is a totally accurate digital representation of 1/3. Oh, there it is
again, at the end of that sentence. It is an analog measure of this
that would lack precision.
Argh, semantics. OK, how about "a binary representation of the *result*
of the expression 1.0/3.0 will always be an approximation." And "an
analog representation of the *result* of the expression 1.0/3.0 *can* be
exact." For example, I could build an analog (i.e, continuous valued)
machine whose ALU performed division by pouring water from one glass into
another (in a loss-free vacuum chamber if you'd like). The glass/water
accululator would be exactly 1/3 full after the above calculation.
Makes you thirsty just thinking about it, doesn't it? :-)
OBCC: Is there any such thing as a stored-program
analog computer?
I guess Babbage's analytic engine would fit that category, but all
of the other analog "computers" that I've heard of (not many) just
performed some fixed calculation. In my book, a stored program with
sequence-control makes the difference between a computer and a
calculator, manufacturer's labelling notwithstanding.
Wasn't Babbage's engine mechanical? Mechanical computers are still
"digital" in the sense that they compute using discrete values/states.
Here is an example which proves that analog machines can execute stored
programs: "go to the store." If you remembered that and went to the
store, then you just answered your own question. (If you didn't go to the
store, you have a bug. :-)
-- Doug