>> "[T]here is a limitation to how small, fast and compact silicon computer
>> chips can be. DNA computers show promise because they do not have the
>> limitations of silicon-based chips."
>>
>> O RLY?
>
> Of course there's a limit. And there's likely a limit on how small/fast
> a DNA-based machine could be as well.

In reality, the nature of matter (and quite possibly time and space 
itself) is quantum. Therefore *every* technology has limits.

Now a DNA computer could potentially be very much smaller than current 
silicon ones. This is not the same statement as "DNA computers do not 
have the limitations of silicon-based chips".

>> "Secondly, the DNA chip manufacture does not produce toxic by-products."
>>
>> Riiight. So because the end product is DNA, a molecule that already
>> exists in nature, therefore you can produce it with no toxic by-products?
>>
>> And the DNA itself wouldn't be toxic, no?
>
> Not unless it codes for something that could cause illness or kill you,
> but who's paying attention anyway.

A virus is nothing more than a stand of DNA or RNA (in some cases coated 
with proteins, but not always). Now, it's highly unlikely that the DNA 
sequence used by a computer would /just happen/ to code for viral 
activity within human cells. It's /completely plausible/ though that if 
some of that stuff gets inside you, it will make the cells it enters 
synthesize endless amounts of some useless protein until they 
prematurely die as a result.

A chemical that kills living cells it touches? Yeah, I'd call that 
pretty toxic. (Still, you presumably don't need to make that much of it...)

> Organic compounds are some of the
> most toxic to us, because they are the most likely to interact. To be
> sure, there are a lot of extremely toxic inorganics as well.

To be sure, there are lots of organic compounds which are "designed" to 
be toxic to us. But even ones that aren't sometimes end up 
"accidentally" being toxic. (E.g., the black widow's venom isn't 
supposed to kill mammals, it's meant to kill insects. And, indeed, it's 
completely harmless to cats and dogs - yet just happens to be lethal to 
humans...)

>> "Last but not the least, DNA computers will be much smaller than
>> silicon-based computers as one pound of DNA chips can hold all the
>> information stored in all the computers in the world."
>
> Storage is not the same as computation.

Agreed.

> No mention as to how fragile that pound of DNA is.

Also agreed, since DNA is very, very definitely biodegradable. (In fact, 
human skin is coated in enzymes designed to snip up RNA, as a protection 
against viruses composed of RNA...)

>> Current computers are much, much larger than strictly necessary mainly
>> due to issues of heat dissipation. You can already make RAM chips that
>> hold absurd quantities of information; it's just that they tend to melt
>> when you switch them on.
>
> I believe the bigger limitation on the amount of information that RAM
> can ultimately hold is more about the lower limit on the size of a
> transistor, rather than heat.

I still suspect that if you weren't worried about heat, you could 
"stack" layers of silicon on top of each other, producing 3D circuitry 
which takes up a fraction of the space.

>> "The capacity to perform parallel calculations, much more trillions of
>> parallel calculations, is something silicon-based computers are not able
>> to do."
>>
>> I beg to differ.
>
> You'd need the pipelines to do it in the chip die. You'd need to build
> very small computational units to get that massively parallel.

True. But, as I understand it, transistors are /already/ "very small". 
The reason that people like Intel and AMD build chips containing several 
thousand million transistors which only comprise two or three "cores" is 
because nobody has really figured out how to make use of lots of cores. 
(Let's face it, Cray have been making vector machines for decades...)

> I don't get how DNA can compute anything. DNA is essentially a coding
> for proteins. What would your end result of a computation be? A glob of
> proteins that mean some sort of result?

If you read some website which actually *explains*, in technical detail, 
what a DNA computer is, you will discover that the DNA is just the 
storage medium. Essentially the DNA is your RAM, and enzymes are your 
computational hardware. So some DNA goes in with the input data encoded 
on it, and new DNA comes out with the result coded on it. (Wikipedia 
indicates that the enzymes function something like an actual Turing 
machine, with the DNA as the "tape".)

>> "In the current technology of logic gates, binary codes from the silicon
>> transistors are converted into instructions that can be carried out by
>> the computer."
>>
>> This is a highly questionable and very muddled statement.
>
> The statement doesn't seem to make a lot of sense.

Indeed.

>> "though it may be very fast in providing possible answers, narrowing
>> these answers down still takes days."
>>
>> This rather suggests that the operation of a DNA computer is
>> non-deterministic (and hence, applicable to a much smaller set of
>> problems than a Turing-complete machine).
>
> Huh? Computers can very quickly give exact answers to a wide class of
> problems.

I'm saying that this description implies that DNA computers aren't 
Turing-complete.

According to Wikipedia, actually they can be. It's just that each 
"computer" is a single molecule, so typically you run millions of them 
at once, in parallel. The slow part, presumably, is synthesizing the 
reactants, and then analysing the reaction products to get your answer 
back afterwards.

> What is needed, really, is more
> improvements on existing algorithms to allow them to operate in parallel
> on simpler computational units. Once a high degree of parallelism is
> met, then we'll see some huge jumps in how fast these silicon machines
> can really work.

I agree.

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