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From: D.M. Procida on 3 Jul 2010 04:16 Rowland McDonnell <real-address-in-sig(a)flur.bltigibbet.invalid> wrote: > Rob <ngonly(a)gmail.com> wrote: > > [snip] > > > I updated a Mini's HD to a standard 500GB a few months ago. Had I known > > about these (or if they were around) I might have given it a go - over > > double the price and higher power consumption (and possibly heat) > > 100% of the electricity that your computer uses gets turned into heat. > > Whatever the power consumption is, that's the heat output. Not strictly true. Some of it gets turned into raw computing power. Only a tiny, tiny amount: r = ec^2 (where r = raw computing power, e = energy, c = speed of light (constant)) At the moment, our computer technology is very wasteful and only manages to convert a tiny bit of that energy into raw computing power; all the rest is lost as heat. But, it is getting much, much more efficient, which is why computers are getting more powerful and energy-efficient. Daniele
From: Rowland McDonnell on 3 Jul 2010 22:21 D.M. Procida <real-not-anti-spam-address(a)apple-juice.co.uk> wrote: > Rowland McDonnell <real-address-in-sig(a)flur.bltigibbet.invalid> wrote: > > > Rob <ngonly(a)gmail.com> wrote: > > > > [snip] > > > > > I updated a Mini's HD to a standard 500GB a few months ago. Had I known > > > about these (or if they were around) I might have given it a go - over > > > double the price and higher power consumption (and possibly heat) > > > > 100% of the electricity that your computer uses gets turned into heat. > > > > Whatever the power consumption is, that's the heat output. > > Not strictly true. <cough> Taken on a long enough timescale, all energy degrades into heat - no exceptions assuming you believe in thermodynamics. The negligible fraction of computer energy use that doesn't turn into heat pretty much straight away is so small as to be utterly irrelevant from the point of view of all practical thermal considerations. So from a practical point of view, a computer drawing 200W electrical power kicks out 200W of heat; and from the strictly accurate point of view, I'm correct to state that 100% of the electricity used by a computer gets turned into heat - the picky might want to see `eventually' tacked on the end of that statement. > Some of it gets turned into raw computing power. Only > a tiny, tiny amount: > > r = ec^2 > > (where r = raw computing power, e = energy, c = speed of light > (constant)) Umm. But all energy degrades to heat in the end. No exceptions. Have you got a link that explains the expression above? 'cos I'm having trouble understanding how it might mean anything - and I can't find anything on the Web about it. Anyway, `raw computing power' - okay, you're saying that's a use of energy. But I can't figure out how the phrase `raw computing power' as it stands in the expression above ties up with the concepts of work and power that I understand. - nor how it avoids degrading into heat in the end. So, here's me trying to understand: What exactly is the quantity `r' specifying? And the constant `e' - where's it come from? What's it's value? And why? And if you're presenting something of the form `r = ec^2', with `e' as energy - well, straight away I can say that the LHS side of the equation has the dimensions of mass rather than pure energy, which is more than a little odd. How is it valid to measure `raw computing power' in kilograms? 'cos that's what you're doing. <shrug> Maybe there is a good explanation - buggered if I can think of it. I can dig the idea of moving electrons up and down in potential or modifying magnetic domains being `work done that's not immediately turned into heat' - but you know, unless you're in a superconducting or specially set up quantum mode, almost all of the energy used in moving an electron around *does* turn into heat, and it all does in the end. For sure there are processes going on that are `work done that doesn't turn /immediately/ into heat' - but, erm... I'm baffled by the expression you present. > At the moment, our computer technology is very wasteful and only manages > to convert a tiny bit of that energy into raw computing power; all the > rest is lost as heat. It all goes to heat in the end - and from a practical point of view, the fraction that takes a long time to turn into heat is negligible, hence my comment above. > But, it is getting much, much more efficient, which is why computers are > getting more powerful and energy-efficient. I thought they had been getting massively less energy efficient, actually - the tiny transistors in use suffer terribly from electrical leakage, and that's all pure waste. Rowland. -- Remove the animal for email address: rowland.mcdonnell(a)dog.physics.org Sorry - the spam got to me http://www.mag-uk.org http://www.bmf.co.uk UK biker? Join MAG and the BMF and stop the Eurocrats banning biking
From: Rowland McDonnell on 4 Jul 2010 00:10
Rowland McDonnell <real-address-in-sig(a)flur.bltigibbet.invalid> wrote: [snip] > And if you're presenting something of the form `r = ec^2', with `e' as > energy - well, straight away I can say that the LHS side of the equation > has the dimensions of mass rather than pure energy, which is more than a > little odd. [snip] Argharghargh ohnonononono oh god no that's seriously embarrassingly wrong. Sorry. Got things the wrong way up in my head. Reciprocal trouble, as a teacher of mine once called it. Anyway: Engaged brain now. Not worked it all the way through, but the point is that the LHS of your expression doesn't have the dimensions of energy - as the RHS states, it's got the dimensions of energy x M^2 L^(-2). So whatever quantity r might be, it's certainly not energy. M = mass, L = length, T = time. r has dimensions of M L^4 T^(-4) Energy has dimensions of M L^2 T^(-2), so: r has dimensions of: or (all working done with pencil and paper): energy x velocity^2 (which is what the RHS says, so no help there except to confirm that I've not slipped up). <shrug> Casting around for alternatives: r has dimensions of mass x velocity^4. And of M L ^2 x acceleration^2 ....and I still don't know what that means. Anyone got a clue? Or a pointer? Or anything? Rowland. -- Remove the animal for email address: rowland.mcdonnell(a)dog.physics.org Sorry - the spam got to me http://www.mag-uk.org http://www.bmf.co.uk UK biker? Join MAG and the BMF and stop the Eurocrats banning biking |