OT: This Swift thing

Discussion in 'Python' started by Sturla Molden, Jun 3, 2014.

  1. I'm not sure where Chris' message comes from, I can't see the original,
    so I'm guessing the context.

    Air cooled cars don't just cool the engine when they are travelling at
    100kmh. Some air-cooled engines used a fan to blow extra air over the
    cooling fins, but many did not. Normal air flow is sufficient to keep
    them in a safe operating temperature, the hot engine warms the air, which
    flows away and is replaced by cooler air.

    It's possible to design CPUs to work the same way. My wife is using a PC
    right now with a 1.66GHz Atom CPU and no CPU fan. Even though the power
    supply fan died, the machine is still running perfectly, with two laptop
    HDDs, and no overheating. 1.66GHz is plenty fast enough for web browsing,
    word processing, email, etc.

    Go back 30 years, and I don't think that the average PC needed a CPU fan.
    Possibly not even a case fan. Just the normal air flow over a small heat
    sink was enough. And of course, your mobile phone has no room for a heat
    sink, unless it's tiny, and no fan. And people expect it to keep working
    even when shoved in their pocket.

    That may be true of water-cooled engines *now*, but it's not a law of
    engineering. Many air-cooled engines do not (did not) require a fan, or
    only needed the extra cooling when stuck idling for long periods in hot
    weather. E.g. Beetles didn't use a fan. (A great idea for Germany, not so
    much for hot and dusty Southern California, as my wife can tell you.)

    Yes, technically water-cooled engines are cooled by air too. The engine
    heats a coolant (despite the name, usually not water these days) which
    then heats the air.
    Steven D'Aprano, Jun 11, 2014
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  2. Sturla Molden

    Roy Smith Guest

    Not water??? I'm not aware of any water-cooled engines which use
    anything other than water. Well, OK, it's really a solution of ethylene
    or propylene glycol in water, but the water is what does most of the
    heat transfer. The glycol is just there to provide freezing point
    depression and boiling point elevation.
    Roy Smith, Jun 11, 2014
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  3. Not the point. There's a minimum amount of energy required to flip a bit.
    Everything beyond that is, in a sense, just wasted. You mentioned this
    yourself in your previous post. It's a *really* tiny amount of energy:
    about 17 meV at room temperature. That's 17 milli electron-volt, or
    2.7×10^-21 joules. In comparison, Intel CMOS transistors have a gate
    charging energy of about 62500 eV (1×10^-14 J), around 3.7 million times

    Broadly speaking, if the fundamental thermodynamic minimum amount of
    energy needed to flip a bit takes the equivalent of a single grain of
    white rice, then our current computing technology uses the equivalent of
    175 Big Macs.

    (There are approximately 50 grains of rice in a gram, and a gram of rice
    is about 1.3 Calories. A Big Mac is about 550 Calories. You do the maths.)
    Steven D'Aprano, Jun 11, 2014
  4. Sturla Molden

    Rustom Mody Guest

    Actually the car-drive and the bit-flip are much more identical than
    different. Its just that the time-scales are minutes/hours in one
    case and nanoseconds or less in the other so our powers of
    visualization are a bit taxed.

    In more detail:

    One drives a car from A to B for an hour (assume no change in
    height above sea level so no potential difference).
    All the energy that was there as petrol has been dissipated as heat.

    A bit flips from zero to one. Pictorially
    (this needs to be fixed-pitch font!):


    However in reality that 'square' wave is always actually sloped


    Now for say CMOS technology, one may assume no currents in both zero
    and one states (thats the C in CMOS). However when its neither zero
    nor one (the sloping part) there will be current and therefore heat.

    So just as the car burns energy in going from A to B, the flipflop
    burns it in going from 0 to 1

    Well thats in the same realm as saying that by E=mc² a one gram stone can yield
    21 billion calories energy.

    [Ive forgotten how the units stack up, so as usual relyin on google
    instead of first principles:


    ie. from a a pragmatic/engineering pov we know as much how to use
    Einstein's energy-mass-equivalence to generate energy as we know how
    to use Landauer's principle to optimally flip bits.
    Rustom Mody, Jun 11, 2014
  5. The point was that said coolant is, itself, cooled via an air/water
    heat exchanger (the radiator -- which in most cars proceeds to then pass
    the now-heated air back over the engine <G>)
    Dennis Lee Bieber, Jun 12, 2014
  6. Would you consider it fair to say that, say, vinegar is "not water"?
    Depending on the type of vinegar, it is typically around 5-10% acetic
    acid, and the rest water. Spirit vinegar can be as much as 20% acetic
    acid, which still leaves 80% water.

    How about brandy, which is typically 35%-60% alcohol, with most of the
    rest being water? Or household bleach, which is typically a 3-6% solution
    of sodium hypochlorite? Or milk (85-90% water)? I think it is fair to
    describe those as "not water". You shouldn't try to put out a fire by
    pouring a bottle of brandy on it.

    Automotive cooling fluid in modern sealed radiators is typically a
    mixture of 50% anti-freeze and 50% water.

    Back in the day, car radiators were *literally* water-cooled in the sense
    that the radiator was filled with 100% water. You filled it from the tap
    with drinking water. In an emergency, say broken down in the desert, you
    could drink the stuff from the radiator to survive. If you tried that
    with many modern cars, you would die a horrible death.
    Steven D'Aprano, Jun 12, 2014
  7. You know, I think that the people of Hiroshima and Nagasaki and Chernobyl
    and Fukushima (to mention only a few places) might disagree.

    We know *much more* about generating energy from E = mc^2 than we know
    about optimally flipping bits: our nuclear reactions convert something of
    the order of 0.1% of their fuel to energy, that is, to get a certain
    yield, we "merely" have to supply about a thousand times more fuel than
    we theoretically needed. That's about a thousand times better than the
    efficiency of current bit-flipping technology.

    We build great big clanking mechanical devices out of lumps of steel that
    reach 25% - 50% of the theoretical maximum efficiency:


    while our computational technology is something of the order of 0.00001%
    efficient. I'm just pointing out that our computational technology uses
    over a million times more energy than the theoretical minimum, and
    therefore there is a lot of room for efficiency gains without sacrificing
    computer power. I never imagined that such viewpoint would turn out to be
    so controversial.
    Steven D'Aprano, Jun 12, 2014
  8. Sometimes it's even more than 50%, at which point
    you really have an antifreeze-cooled engine. :)
    Gregory Ewing, Jun 12, 2014
  9. The way I understand it, you're citing an extremely theoretical
    minimum, in the same way that one can point out that we're a long way
    from maximum entropy in a flash memory chip, so it ought to be
    possible to pack a lot more data onto a USB stick. The laws of physics
    tend to put boundaries that are ridiculously far from where we
    actually work - I think most roads have speed limits that run a fairly
    long way short of c.

    Chris Angelico, Jun 12, 2014
  10. Sturla Molden

    Gene Heskett Guest

    There have been cases where that 50% may have been exceeded actually
    driving on the streets.

    At least 3 decades back, not too long before caddy came out with the
    northstar engine, which was rigged to get you home at a reasonable speed
    even if the radiator had been holed & the coolant lost. They used a wee
    bit of the knowledge gained from keeping Smokey Yunick is experimenting
    cash. He had an old VW Rabbit that was both a parts car, and the test
    bed. Two cylinder motor, I suspect built on a Harley 78cid crankcase, no
    radiator, no air cooling. Ceramic cylinders and pistons, it ran at a
    quite high internal temperature because the cylinders were insulated from
    losing heat by fiberglass blankets. It displaced 78 cid, made about 150
    HP, and got well over 120 mpg running around in Daytona Beach. The one
    magazine article said it hadn't lost a stoplight grand prix ever but
    Smokey stopped that by making whoever was driving it, 100% responsible for
    any tickets it collected.

    It would have been gawdawful expensive to put it into production since
    those 2 cylinders & pistons cost more than the complete V8 Northstar

    I thought it was one radically cool idea at the time. And I am amazed
    that something like it has not invaded the automotive world what with all
    the emphasis on both high mileage & decent horsepower caused by the high
    petro prices. Today I'd imagine a new cat converter might need to be
    built because at those temps and compression ratio's, I can see a hugely
    illegal amount of the various nitrogen oxides the EPA wouldn't tolerate.

    Cheers, Gene Heskett
    "There are four boxes to be used in defense of liberty:
    soap, ballot, jury, and ammo. Please use in that order."
    -Ed Howdershelt (Author)
    Genes Web page <http://geneslinuxbox.net:6309/gene>
    US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS
    Gene Heskett, Jun 12, 2014
  11. Um, yes?

    Hands up anyone who thinks that today's generation of USB sticks will be
    the highest capacity ever, that all progress in packing more memory into
    a thumb drive (or the same memory into a smaller drive) will cease
    effective immediately?


    "186,000 miles per second: not just a good idea, it's the law"

    There's no *law of physics* that says cars can only travel at the speeds
    they do. Compare how fast a typical racing car goes with the typical
    60kph speed limit in suburban Melbourne. Now compare how fast the
    Hennessey Venom GT goes to that speed limit.


    Speed limits for human-piloted ground-based transport ("cars") are more
    based on social and biological factors than engineering ones. Similarly,
    there are biological factors that force keyboards to be a minimum size.
    We probably could build a keyboard where the keys were 0.1mm square, but
    what would be the point? Who could use it? Those social and biological
    factors don't apply to computing efficiency, so it's only *engineering*
    factors that prevent us from being able to run your server off a watch
    battery, not the laws of physics.

    It is my contention that, had Intel and AMD spent the last few decades
    optimizing for power consumption rather than speed, we probably could run
    a server off, well, perhaps not a watch battery, but surely a factor of
    100 improvement in efficiency isn't unreasonable given that we're just
    moving a picogram of electrons around?
    Steven D'Aprano, Jun 12, 2014
  12. Current draw of CMOS circuitry is pretty much zero when
    nothing is changing, so if you didn't care how slow it ran,
    you probably could run a server off a watch battery today.
    Users wouldn't like waiting a week for their web pages to
    load, though...
    Gregory Ewing, Jun 12, 2014
  13. Sturla Molden

    Rustom Mody Guest

    I am bewildered by this argument...

    [Heck Ive recently learnt that using ellipses is an easy way to
    produce literature... So there...]

    This is fine and right.
    I personally would pay more if my PCs/laptops etc were quieter/efficient-er.
    So we agree... upto here!

    Now you (or I) are getting completely confused.

    If you are saying that the Hennessey Venom (HV) is better than some
    standard vanilla Ford/Toyota (FT) based on the above, thats ok.

    In equations:
    maxspeed(HV) = 250 mph
    maxspeed(FT) = 150 mph
    so HV is better than FT.


    But from your earlier statements you seem to be saying its better
    250 mph is closer to 186,000 mps (= 670 million mph) than 150 mph

    Factually this is a correct statement.

    Pragmatically this is as nonsensical as comparing a mile and a

    As best as I can see you are confused about the difference between
    science and engineering.

    Saying one car is better engineered than another on direct comparison
    (150mph<250mph) is ok

    Saying one car is better than another because of relation to physics
    limits (c-150>c-250) is confusing science and engineering.

    Likewise saying AMD and Intel should have done more due diligence to
    their clients (and the planet) by considerging energy efficiency is right
    and I (strongly) agree.

    But compare their products' realized efficiency with theoretical limits like
    Landauers is a type-wrong statement
    Rustom Mody, Jun 12, 2014
  14. I'm not making any value judgements ("better" or "worse") about cars
    based on their speed. I'm just pointing out that the speed limits on our
    roads have very little to do with the speeds cars are capable of
    reaching, and *nothing* to do with ultimate limits due to the laws of

    Chris made the argument that *the laws of physics* put limits on what we
    can attain, which is fair enough, but then made the poor example of speed
    limits on roads falling short of the speed of light. Yes, speed limits on
    roads fall considerably short of the speed of light, but not because of
    laws of physics. The speed limit in my street is 50 kilometres per hour,
    not because that limit is a law of physics, or because cars are incapable
    of exceeding 50kph, but because the government where I live has decided
    that 50kph is the maximum safe speed for a car to travel in my street,
    rounded to the nearest multiple of 10kph.

    In other words, Chris' example is a poor one to relate to the energy
    efficiency of computing.

    A more directly relevant example would have been the efficiency of heat
    engines, where there is a fundamental physical limit of 100% efficiency.
    Perhaps Chris didn't mention that one because our technology can build
    heat engines with 60% efficiency, which is probably coming close to the
    practical upper limit of attainable efficiency -- we might, by virtue of
    clever engineering and exotic materials, reach 70% or 80% efficiency, but
    probably not 99.9% efficiency. That's a good example.

    Bringing it back to computing technology, the analogy is that our current
    computing technology is like a heat engine with an efficiency of
    0.000001%. Even an efficiency of 1% would be a marvelous improvement. In
    this analogy, there's an ultimate limit of 100% imposed by physics
    (Landauer's Law), and a practical limit of (let's say) 80%, but current
    computing technology is so far from those limits that those limits might
    as well not exist.

    "Better" is your word, not mine.

    I don't actually care about fast cars, but if I did, and if I valued
    speed above everything else (cost, safety, fuel efficiency, noise,
    environmental impact, comfort, etc) then yes, I would say 250 mph is
    "better" than 150 mph, because 250 mph is larger.

    And yet you're going to disagree with it, even though you agree it is

    This makes no sense at all.

    Your two statements about speeds are logically and mathematically
    equivalent. You cannot have one without the other.

    Take three numbers, speeds in this case, s1, s2 and c, with c a strict
    upper-bound. We can take:

    s1 < s2 < c

    without loss of generality. So in this case, we say that s2 is greater
    than s1:

    s2 > s1

    Adding the constant c to both sides does not change the inequality:

    c + s2 > c + s1

    Subtracting s1 + s2 from each side:

    c + s2 - (s1 + s2) > c + s1 - (s1 + s2)
    c - s1 > c - s2

    In other words, if 250mph is larger than 150mph (a fact, as you accept),
    then it is equally a fact that 250mph is closer to the speed of light
    than 150mph. You cannot possibly have one and not the other. So why do
    you believe that the first form is acceptable, but the second form is

    I do not understand what confusion you think you see here.

    If we agree on the value judgement "greater top speeds are always
    better", and the law of physics "c is the upper-limit to speeds", then
    the following two statements are logically equivalent:

    "Car HV is better than car FT because the HV has the greater top speed."

    "Car HV is better than car FT because the HV's top speed is closer to c
    than the FT's top speed."

    These sorts of value judgments are independent of the *cause* of the
    upper limit. Sticking to Chris' example of speed, if we agree that faster
    travel is better than slower travel, then in the state of Victoria,
    Australia, the ultimate upper-limit on (legal) speed is 110kph. If we
    decide to value faster speeds, then the Hume Freeway with its 100kph
    speed limit is better than my suburban back street with a 50kph speed
    limit, even though the limit is a social restriction, not an engineering
    limit or physics limit.

    If I were arguing that there are no engineering limits prohibiting CPUs
    reaching Landauer's limit, then you could criticise me for that, but I'm
    not making that argument.

    I'm saying that, whatever the practical engineering limits turn out to
    be, we're unlikely to be close to them, and therefore there are very
    likely to be many and massive efficiency gains to be made in computing.
    Steven D'Aprano, Jun 12, 2014
  15. The point isn't so much the legal or safe limit as that that's the
    speed of most driving. That is to say: Around here, most cars will
    travel at roughly 50 kph, which is a far cry from c. There are other
    reasons than physics for choosing a speed.
    As long as we accept that this is purely in a mathematical sense.
    Let's not get into the realm of actual speeds greater than c.
    And at this point the calculation becomes safe again, and obvious
    common sense. (Or alternatively, substitute Mach 1 for c; it's not a
    hard limit, but there are good reasons for staying below it in
    practical application - most airliners cruise a smidge below the speed
    of sound for efficiency.)
    And this I totally agree with. The limits of physics are so incredibly
    far from where we now are that we can utterly ignore them; the limits
    we face are generally engineering (with the exception of stuff
    designed for humans to use, eg minimum useful key size is defined by
    fingers and not by what we can build).

    Chris Angelico, Jun 12, 2014
  16. Sturla Molden

    Gene Heskett Guest

    Thats a bit too blanketish a statement, we do see it in the real world.
    Some of the electronics stuff we've been using for nearly 50 years
    actually runs into the e=MC^2 effects, and it affects their performance in
    pretty deleterious ways.

    A broadcast power klystron, like a 4KM100LA, which is an electron beam
    device that does its amplifying by modulating the velocity of an electron
    beam which is being accelerated by nominally a 20,000 volt beam supply.
    But because of the beam speed from that high a voltage brings in
    relativity effects from e=MV^2 mass of the electrons in that beam, an
    equal amount of energy applied to speed it up does not get the same
    increase in velocity as that same energy applied to slow it down decreases
    it. This has the net effect of making the transit time greater when under
    high power drive conditions such as the sync pulses of the now out of
    style NTSC signal. The net result is a group delay characteristic that is
    uncorrectable when the baseband video is where you are trying to correct
    it. In a few words, the shape of the sync signal is damaged. Badly.

    Because most transmitters of that day used separate amplifiers for the
    audio, and the receivers have used the 4.5 mhz difference signal to
    recover the audio in the receiver for the last 63+ years, this "Incidental
    Carrier Phase Modulation" noise is impressed into the detected audio. And
    I am sure that there are many here that can recall back a decade that the
    UHF stations in your area, all had a what was often called "chroma buzz"
    in the audio that was only about 50 db down. Ear fatiguing at best.
    Market share effecting too. And that translates directly into station
    income minus signs.

    It was fixable, but at an additional cost in efficiency of about -20%, but
    consider what that 20% costs when a station using a 30kw rated
    transmitter, actually pulls around 225 kwh from the powerline for every
    hour it is on the air. Bean counters have heart attacks over such

    Cheers, Gene Heskett
    "There are four boxes to be used in defense of liberty:
    soap, ballot, jury, and ammo. Please use in that order."
    -Ed Howdershelt (Author)
    Genes Web page <http://geneslinuxbox.net:6309/gene>
    US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS
    Gene Heskett, Jun 12, 2014
  17. Sturla Molden

    Rustom Mody Guest

    You got a keen eye Chris -- didn't notice that!
    And captures my point better than my long-winded attempts
    Rustom Mody, Jun 13, 2014
  18. Well, yes, it is in the mathematical sense, and it doesn't require any
    actual physical thing to travel at faster than light speed. There is no
    implication here that there is something travelling at (c + s1). It's
    just a number.

    But note that even in *real* (as opposed to science fiction, or
    hypothetical) physics, you can have superluminal speeds. Both the phase
    velocity and group velocity of a wave may exceed c; the closing velocity
    of two objects approaching each other is limited to 2c. Distant galaxies
    are receding from us at greater than c. There are other situations where
    some measurable effect can travel faster than c, e.g. the superluminal
    spotlight effect.

    Steven D'Aprano, Jun 13, 2014
  19. Sturla Molden

    Roy Smith Guest

    In a car, the water is the important part (even if it's only a 50%
    component). The primary job of the circulating coolant is to absorb
    heat in one place and transport it to another place. That requires a
    liquid with a high heat capacity, which is the water. The other stuff
    is just there to help the water do its job (i.e. not freeze in the
    winter, or boil over in the summer, and some anti-corrosive action
    thrown into the mix).

    When you said, "usually not water these days", that's a misleading
    statement. Certainly, it's "not pure water", or even "just water". But
    "not water" is a bit of a stretch.

    With vinegar, the acetic acid is the important component. The water is
    just there to dilute it to a useful working concentration and act as a
    carrier. People are 90% water too, but I wouldn't call a person
    "water". I would, however, as a first-order description, call the stuff
    circulating through the cooling system in my car, "water".
    But, I could do that right now, with my car (well, not the drinking
    part) . In an emergency, I could fill my cooling system with pure
    water, and it would work well enough to get me someplace not too far
    away where I could get repairs done.
    Roy Smith, Jun 13, 2014
  20. You're comparing a one-use device to a trillion-use device. I think
    that's unfair.

    Tell me when you find an atom splitter that works a trillion times.
    Then tell me what it's efficiency is, because it's not nearly 0.1%.
    Joshua Landau, Jun 15, 2014
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