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Old Nov 4, 2012, 05:24 PM   #1
Tucson Allen
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Are we looking at iMac design the wrong-way-about?

I’m beginning to think we’re looking at the 2012 iMac design the wrong-way-about, functionally speaking. An obvious clue is that there is only one fan to be seen, down from three in the 2011 iMac. (No ODD, no ODD fan, of course.) This implies a marked improvement in the heat management picture. It says, in effect, that far from worrying that the cooling will be a weak spot in the design, we should wondering about what justified the fan change.

This change implies that the hump in the middle of the back grew not out a desire for a dramatically thin edge, but was something needed to produce a new cooling functionality. This implies that the edges needed to be narrowed to support the new cooling functionality at the center. The 5 mm edge represents the practical limit of this change, producing a startling side-on view emphasizing the stark newness of the design.

I have several posts exploring the implications of the design for convection cooling. In brief, convection fuels the movement of heated air in and out of the computer. When air is heated by the components it registers a change in its temperature/pressure complex: it rises and tends to expand when entering a larger enclosing volume, which the hump provides, progressively. Because components nearer an edge face a larger volume to the center, they will tend to flow upward and to the center. The air at the top will also tend to expand and move to the center (down and tending to the center), aided by the fan at the top left discharging at the lower center.

The fan discharge near the vent grid has little effect on venting the air to the outside. It merely concentrates the hot air in the path of the convection flow triggered by the heating. The pressure differential of the air and its expansive power, input vs. output, creates the venting and maintains the intake at the bottom.

I think we are looking at a design, functional at bottom, of someone capable of carrying a design inspired by form into the realm of the beautiful: a genius.

My question to you is, have you found reasons to disagree? What about the mysterious black objects to the left and right? Are they merely to concentrate the convection flow more effectively?
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Old Nov 4, 2012, 06:11 PM   #2
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I don't think the hump in the back got any bigger, at least as far as I can tell from the Engadget hands-on photos:

http://www.engadget.com/photos/apple...ds-on/#5382107

At any rate, the whole thing is still thinner and lighter than my 24 inch 2009 iMac
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Old Nov 4, 2012, 06:46 PM   #3
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Originally Posted by Tucson Allen View Post
What about the mysterious black objects to the left and right? Are they merely to concentrate the convection flow more effectively?
Speakers are my guess.
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Old Nov 4, 2012, 06:52 PM   #4
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Speakers are my guess.
I thought they were just the screen...it is ridiculously thin at those points.
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Old Nov 4, 2012, 07:36 PM   #5
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The fan discharge near the vent grid has little effect on venting the air to the outside. It merely concentrates the hot air in the path of the convection flow triggered by the heating. The pressure differential of the air and its expansive power, input vs. output, creates the venting and maintains the intake at the bottom.
I think the idea that the air when heated is then confined to the centre of the bulge is just one step in the cooling process. The iMac now solely relies on a single fan to move hot air out of the case.

It would make sense to to draw a conclusion that the cool air is taken in at the bottom of the case, this is then heated by various components in the case and the hot air confined to the center of the case is then left to rise via convection to the top of the case. Now there is no slot on this model for the air to escape so it now relies on the fan mounted with the intake situated toward the top of the case to expelled the heated air while simultaneously cooling the cpu and gpu as the air is expelled via the slot gap underneath the stand. Cooling of the air is also achieved via the aluminum backplane of the case which will also greatly reduce the case temperatures.

There are many benefits to this design one being the hot air from the major components is directly vented out of the case. IMO I think the use of convection cooling is used to less extent to naturally cool the new iMac and that this cooling concept has partly been driven via the 5 mm edge idea and not the other way around. While I can see your point I think the design of the new iMac is mostly driven by function follows form.

On the positive I think the new design is creative and has a logical process behind it. I can really see it being a thermally cooler computer than the previous model and a step forward in terms of reduced impact computing. All of the technological advancements are going in to small form factor computing at the moment so it only makes sense to use those already well established principles in the new iMac.

I just hope it works out as well in my head as it does in reality.
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Old Nov 4, 2012, 08:41 PM   #6
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Until I see a model in person it is hard to say. From the pictures I feel the design may be a little different than I prefer. The thin edges contrast from the bowed back and I always picture what it would look like on my desk. I am learning to let go of the optical drive; I see its useful life fading fast.

I do say the lack of upgradability sounds daunting but I guess when its time to upgrade from my current iMac I will be in a position to custom order what I want and not base it on what I can afford...
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Old Nov 4, 2012, 10:05 PM   #7
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Consider the case of Dr. Franklin’s stove

It would make sense to draw a conclusion that the cool air is taken in at the bottom of the case, this is then heated by various components in the case and the hot air confined to the center of the case is then left to rise via convection to the top of the case.

Now there is no slot on this model for the air to escape so it now relies on the fan mounted with the intake situated toward the top of the case to expelled the heated air while simultaneously cooling the cpu and gpu as the air is expelled via the slot gap underneath the stand. Cooling of the air is also achieved via the aluminum backplane of the case which will also greatly reduce the case temperatures.

...........

Yes, the aluminum case would act as a conductor of heat, as a heat sink, and as a source of heat being radiated away. No, the fan will not be effective in blowing heat out the intakes at the bottom—or out the vents below the center of the back. In the first place, the effect of the fan is largely contained within the case. If you’ve ever tried to cool a room by blowing air in or out of it with a fan at a window, you may have discovered that without its being mounted in a board blocking the window around the fan there is no effective coupling of the inside to the outside air. In short, without such coupling the fan’s effect is felt mostly within the room. Further, if the fan in the iMac was coupled to the vents on the back, it would defeat the outlet of convection cooling and the iMac would promptly self-destruct.

When it comes to moving the air in and out of the iMac, convection is the only game in town. The fan cools hot-spots and heat-sinks by maintaining a positive airflow over them with sufficient velocity. But this heated air remains to be vented. This requires some other force. Convection relies on heat; it is an engine driven by heat. In the present case the dynamic tendency of heated air to rise is modified by an effect on pressure due to the increasing volumetric gradient of the hump on either side (and at the top). In the special case of top layer, the two up-flows from the sides are constrained to move to the center. There they combine and form a downward counterflow connecting to the pressure drop in the area of the vent. The fan does its part in this.

This is counter-intuitive. The system of Ben Franklin’s stove may be instructive. He invented a stove for his own use which drew down over the coals to a flue running under the floor and connecting to a chimney, no doubt depending on convection to create a sufficient draft. (If you have lived with wood-fired stoves and their stove-pipes running here and there to a chimney, dripping down creosote in rain and subject to chimney fires, you may judge his reasons.) His only reservation was that his housekeeper was not to try to start the fire. It must have required that the chimney be drawing very well indeed before the fire could be safely lit.

Last edited by Tucson Allen; Nov 4, 2012 at 10:09 PM. Reason: typo
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Old Nov 5, 2012, 07:15 AM   #8
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When it comes to moving the air in and out of the iMac, convection is the only game in town. The fan cools hot-spots and heat-sinks by maintaining a positive airflow over them with sufficient velocity. But this heated air remains to be vented. This requires some other force. Convection relies on heat; it is an engine driven by heat. In the present case the dynamic tendency of heated air to rise is modified by an effect on pressure due to the increasing volumetric gradient of the hump on either side (and at the top). In the special case of top layer, the two up-flows from the sides are constrained to move to the center. There they combine and form a downward counterflow connecting to the pressure drop in the area of the vent. The fan does its part in this.
I think you are trying to make this cooling system too complicated. I agree with the principle of convection but what you are referring to is the 2011 iMac. It used the exact process you are talking about. The the 2013 relies much less on convection and lets the central fan do most of the work. If you look closely on the internal case shot there is an inlet for the fan at the top of the case which draws air in to be blown down a tube to the center point of the case. This happens to align with the slot under the case stand which will indefinitely be the place where air is forced out of the machine via the fan.

Convection is only a weak force when confined to such a small space as the iMac. It would be next to useless to use convection with a small exit in the center of the case. This would defeat the hole point of rising hot air. Hence why the 2011 iMac has a long slot gap running across the entire length of the top of the case. I assure you nearly all laptops have air channels to blow hot air thought the case chassis and it will work perfectly fine for the iMac unit. You will be able to physically feel the hot air coming out of like a hairdryer, convection does not have such an effect in this situation.
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Old Nov 5, 2012, 09:23 AM   #9
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I have 2010 model iMac and between the two designwise there is no difference when staring head on i still see the same chin and edge to edge glass. I guess I will hang to what I got for while, as the loss of the DVD drive is going to hurt me ATM I am trying buy whatever TV shows I can find on iTunes.

I personally don't look at the computer from the side where it is positioned so ATM I have no desire to update my iMac even though I am missing the USB 3.0 and thunderbolt ports but that's we're my MacBook retina will come in.

I prefer to wait for the rumoured iMacs retina display with this years model screen being improved anti glaire and screen closer to glass the introduction of retina would make it the best monitor on the market dare I say even better than MacBook retina.
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Old Nov 6, 2012, 03:46 PM   #10
Tucson Allen
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I’m betting that the 2012 iMac has better cooling

After reading your responses to my post (my thanks for them) I‘ve decided to wait for the new iMacs, based on one thing: the fact that there’s only one fan confirmed my analysis for me: cooling should not be a problem in the 2012s. You don’t reduce the number of fans in a computer that runs a little hot unless you have something else going for your new design. My second iMac was cooled entirely by convection: no fan. The refurbished 2011s at the Apple Store were looking mighty tempting when I posted (they’re almost gone now), but I’m glad I waited.
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Old Nov 8, 2012, 09:07 PM   #11
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The 21.5” iMac is a different case

Today I decided to go with the new 21.5 iMac with the Geforce GTX 650M, CPU boost, and 1 TB HDD. Its 5400 rpm drive required some thought. I discovered that it was more expensive and that it ran cooler. Ah, it was chosen because it ran cooler. The 7200 rpm drive was OK in the 27” iMac because the heating/cooling picture is different. The smaller case evidently presents some lack of potential by contrast: I had to rethink my previous analyses somewhat. I could sense some of the difficulties that might arise in removing a 5.2” section in width from the case, in forming, in appearance, and in thermal function. Still, the fact that Apple design looks to have taken this into account in their employing the 5400 rpm drive—evidently because it runs cooler, and by all accounts, significantly cooler—I am betting on the smaller one. And it is, of course, a bet.

At this point I had to reconsider my decision to go with 21.5” iMac: With its screen being almost 19” wide and 10.5” high, I see it as fulfilling both my computing and movie viewing needs. I confirmed this by viewing a 16X9 movie on my 20” iMac 4,1 (The Wind and the Lion). The movie occupied only about 60% of the screen height, yet was viewable well away from the desk. With the full 10.5 inches available in 16X9 it should do very well. Checking various viewing standards for different screen sizes on the internet and taking into account the work distance at the desk and my seating distance for viewing only confirmed this. Money certainly is a consideration, but good enough is sufficient.
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Old Nov 8, 2012, 09:11 PM   #12
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Originally Posted by Tucson Allen View Post

The fan discharge near the vent grid has little effect on venting the air to the outside. It merely concentrates the hot air in the path of the convection flow triggered by the heating. The pressure differential of the air and its expansive power, input vs. output, creates the venting and maintains the intake at the bottom.
I think Apple is quickly but quietly heading towards their patent for ionic air cooling. They have already established the airflow channels, my guess is this form factor will stay but they will truly add it next year without any fanfare.

http://appleinsider.com/articles/12/...-computer-fans
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Old Nov 10, 2012, 12:57 PM   #13
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Originally Posted by Tucson Allen View Post
I’m beginning to think we’re looking at the 2012 iMac design the wrong-way-about, functionally speaking. An obvious clue is that there is only one fan to be seen, down from three in the 2011 iMac. (No ODD, no ODD fan, of course.) This implies a marked improvement in the heat management picture. It says, in effect, that far from worrying that the cooling will be a weak spot in the design, we should wondering about what justified the fan change.

This change implies that the hump in the middle of the back grew not out a desire for a dramatically thin edge, but was something needed to produce a new cooling functionality. This implies that the edges needed to be narrowed to support the new cooling functionality at the center. The 5 mm edge represents the practical limit of this change, producing a startling side-on view emphasizing the stark newness of the design.

I have several posts exploring the implications of the design for convection cooling. In brief, convection fuels the movement of heated air in and out of the computer. When air is heated by the components it registers a change in its temperature/pressure complex: it rises and tends to expand when entering a larger enclosing volume, which the hump provides, progressively. Because components nearer an edge face a larger volume to the center, they will tend to flow upward and to the center. The air at the top will also tend to expand and move to the center (down and tending to the center), aided by the fan at the top left discharging at the lower center.

The fan discharge near the vent grid has little effect on venting the air to the outside. It merely concentrates the hot air in the path of the convection flow triggered by the heating. The pressure differential of the air and its expansive power, input vs. output, creates the venting and maintains the intake at the bottom.

I think we are looking at a design, functional at bottom, of someone capable of carrying a design inspired by form into the realm of the beautiful: a genius.

My question to you is, have you found reasons to disagree? What about the mysterious black objects to the left and right? Are they merely to concentrate the convection flow more effectively?
I think you're being overly optimistic. The iMac, pretty much since its late 2005 redesign has been steadily on a course to become thinner than necessary and while the CPUs used since the PowerPC 970FX (G5) and the Intel Core Duo have also dropped in heat requirements since then, they haven't by THAT much. Really, the whole point to the iMac is to save space where the whole point to an actual proper desktop is to utilize it. Toward that end the iMac has become increasingly unreliable. I work at an Apple Authorized Service Provider and the iMac is the #1 machine that comes in for non-accidental-damage. I'm confident that what will effect the most positive change in terms of heating and reliability will be the change to 2.5" hard drives and other laptop based components in the 21.5" iMac. Sure from a functionality standpoint it is a downgrade; but it terms of it being a reliably long-lasting machine, I think it has just made some serious headway. As for the 27" iMac, I don't care where you position the fans, there are a lot of heat generating components in that machine. There always have been. But now they've removed one component (along with a couple fans, if I understand correctly) that didn't really generate all that much heat, kept all of the other heat-generating components just the same and made it thinner, if not way thinner than would otherwise negate the removal to begin with. So really, we might have a LESS reliable and MORE hot-running 27" iMac than before. It's all conjecture as these machines aren't out yet, and thusly they are not in my shop for repair yet, but I'm not overly confident in the 27" iMac. But 21.5" iMac, I'm very much hopeful that I can start confidently recommending them to people that would otherwise buy the Mac mini but want more ooomph.
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Old Nov 10, 2012, 02:41 PM   #14
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I think you're being overly optimistic. The iMac, pretty much since its late 2005 redesign has been steadily on a course to become thinner than necessary and while the CPUs used since the PowerPC 970FX (G5) and the Intel Core Duo have also dropped in heat requirements since then, they haven't by THAT much. Really, the whole point to the iMac is to save space where the whole point to an actual proper desktop is to utilize it. Toward that end the iMac has become increasingly unreliable. I work at an Apple Authorized Service Provider and the iMac is the #1 machine that comes in for non-accidental-damage. I'm confident that what will effect the most positive change in terms of heating and reliability will be the change to 2.5" hard drives and other laptop based components in the 21.5" iMac. Sure from a functionality standpoint it is a downgrade; but it terms of it being a reliably long-lasting machine, I think it has just made some serious headway. As for the 27" iMac, I don't care where you position the fans, there are a lot of heat generating components in that machine. There always have been. But now they've removed one component (along with a couple fans, if I understand correctly) that didn't really generate all that much heat, kept all of the other heat-generating components just the same and made it thinner, if not way thinner than would otherwise negate the removal to begin with. So really, we might have a LESS reliable and MORE hot-running 27" iMac than before. It's all conjecture as these machines aren't out yet, and thusly they are not in my shop for repair yet, but I'm not overly confident in the 27" iMac. But 21.5" iMac, I'm very much hopeful that I can start confidently recommending them to people that would otherwise buy the Mac mini but want more ooomph.
You could be right. Your experience with 21.5 and 27 iMacs is extremely helpful. I am assuming that the thin-edge design made a fundamentally changed approach to the convection “chimney” necessary—and that this led to an opportunity for a brilliant improvement in design functionality. With the thin edges the central hump could be formed into a convection engine. Thinking in terms of Boyle’s Law, heating a gas results not merely a temperature change but also involves a pressure change such that if confined in a constant volume, the gas registers an increase in pressure—or, if the gas is free to expand, it will expand with a corresponding temperature drop. This made the thinness a virtue, giving the heated gas a centering bias, and the gas—air—rising to the top, a downward thrust, reenforced by the fan.

The shape of the hump is complex, likened to a teardrop. The point of maximum extension of the back occurs at the vent screen. This means that all flows come together here, the pressured flows acting as thrust. Because of the venting the micro effect is a local pressure drop, reinforcing the complex flow patterns. I judge that the vent size is “tuned” to maximize the flow-through of the enclosure. A vent too large could stultify the desire convection actions.

The expanding heated air does not exit via the intakes in the chin at the bottom. The general tendency of the air inside as its being heated is to rise, creating a partial vacuum at the intakes, helped by their being made of aluminum, an excellent conductor of heat. This causes the air-intake tubes to play a part in the overall chimney effect.

I think it’s an outstanding design. This doesn’t mean that it solves the heat problem of the previous iMacs, but the very quality of the design implies a very knowledgeable designer. Intuitively I register the fact that only one fan is used where two were before is an indication that the other fan isn’t needed—because cooling and venting has been substantially improved. The 5400 rpm HDD in the 21.5 iMac indicates to me that something about the smaller design made the cooler operation of the (more expensive) drive necessary. There is at present no indication that a second fan is necessary. These conjectures lead me to think the 27 iMac is really improved in its heat management. In a way, the 27 iMac has a longer chimney, more room to accelerate the flows. But in the 21.5, which I intend to order, the 5400 rpm drive can’t be far behind with its cooler CPU and GPU.
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Old Nov 10, 2012, 02:51 PM   #15
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I like the OP's post and think you are onto something ...

My question is this ... when they had the hands on event, did no one touch the back of the iMac to see how hot it was? Possibly load up an app to give temp readings?

I am loving this design and if the hardware can take the heat and not kill eachother because of it, this thing will be an amazing center piece in an office!!
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Old Nov 10, 2012, 03:32 PM   #16
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As conjectured in other discussion threads, there may be several logical explanations for the use of the 5400rpm 2.5" drive in the smaller 21.5" iMac:

1) The smaller screen size left no room for a thick 3.5" drive mount in the deeper "bulge" area, so they had to use a thinner 2.5" drive off to the side more where it thins rapidly.

2) The desire for a 1 TB capacity in a 2.5" drive was only available in 5400rpm class drives. To use a 7200 rpm drive would have required dropping the capacity to 750GB if the 2.5" size was mandatory.

3) Modern 5400rpm 2.5" drives may perform at the same level as 7200rpm 3.5" drives due to data density, smaller/quicker moving masses, large caches, etc.

4) Less heat produced with 5400rpm drives (possibly not a real issue relative to other, much larger heat sources in the case).

5) The available BTO with the Fusion drive would obscure any slight performance issues with the 5400 rpm hard drive (if any).


And ... your analysis of the case and airflow design is very interesting ...



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Old Nov 10, 2012, 05:07 PM   #17
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For reference:


For anybody reading this the re-designed 2012 iMac is effectively an enhanced MacBook Pro. Same simple design like the mbp the iMac has now got a logic board with cpu, gpu, msata, ram, cooling fan and exhaust outlet. Separate power supply, speakers and hdd. Other components like WiFi, Bluetooth, IR sensor cannot be seen on this image. There is not special cooling system here just an oversized mbp strapped on to an improved cinema display. If the reliability of laptops and the mbp's is anything to go by the new iMac is a more encompassing cooling system that we can expect at least to be on par with the mbps. As long as you are not rendering, encoding or gaming for long sessions all the time then I could expect great things from this revised iMac wth cool running componants at idle..

Some of these ideas for cooling systems, especially the positive charged cooling system looks promising for future designs.

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Old Nov 10, 2012, 06:56 PM   #18
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If the reliability of laptops and the mbp's is anything to go by the new iMac is a more encompassing cooling system that we can expect at least to be on par with the mbps. As long as you are not rendering, encoding or gaming for long sessions all the time then I could expect great things from this revised iMac wth cool running componants at idle..
do they overheat if you are using them heavily for long periods? how long is long periods?
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Old Nov 10, 2012, 07:01 PM   #19
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Interesting computer cooling strategies

I was thinking of your comments and I remembered that the Alaskan pipeline is cooled by heat pipes to maintain the permafrost under supporting pillars. In checking on this I found laptops may have heat pipes in connection with their heat sinks <http://en.wikipedia.org/wiki/Heat_pipe>. The copper tubes are heat pipes connected to a radiator:

[I was unable to upload this image it doesn’t have an HTTP address]

A different system is show in a laptop connecting two solid interfaces:

[I was unable to upload this image—go to the URL above]

The heat pipes contain a gas whose density is adjusted to be effective as a refrigerant, vaporized at the site to be cooled and condensing at the target interface, as in a common refrigerator.

Note, however, that these strategies, where used, move or spread out hot-spot conditions within the computer: getting the heat outside the computer is the job of convection in iMacs. The aluminum case plays its part, too, but without convection cooling the iMac would be in deep trouble.

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Old Nov 10, 2012, 07:17 PM   #20
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i am sooo jonesing for the new iMac, any speculation on when in December for the release?

I sold my gasser heli in order to have the money for it! Will be selling my mid-2007 24" as soon as I get this new one!
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Old Nov 10, 2012, 07:26 PM   #21
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For reference:
Oh, there's the picture. I was reading this thread earlier wondering where a picture was, and couldn't be bothered to search for one.

Someone said earlier about those black things on the right and left (The things with the large round holes and gaps on the bottom?) I think those are definitely the speakers.

Unless we're talking about the much larger black things on the right and left? Can't think of what those are.

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As long as you are not rendering, encoding or gaming for long sessions all the time then I could expect great things from this revised iMac wth cool running componants at idle..
Well, I'll be using it for those things pretty much...except gaming...don't really game much.

I would link to my most recent video (To demonstrate what I regularly do) but I don't want people to go off topic and talk about how bad it is (You need the balls to show it to a forum and then people like to go completely offtopic* and move over to talking about the video).

I think I might get an external Thunderbolt graphics card if the new iMac doesn't handle it that well...I think it should hold out well because it's CUDA certified (So excited to try CUDA).

*I'm now going offtopic...

----------

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do they overheat if you are using them heavily for long periods? how long is long periods?
I'm not entirely sure, I'm not the one t be getting real answers from on this, but I think I remember about a month after the 15" Retina release, there were reports that the cooling sucked.

I wouldn't be surprised (Like people have said earlier) that the iMac will generally be better at cooling anyway.
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Old Nov 10, 2012, 08:38 PM   #22
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Originally Posted by oobybiggs View Post
do they overheat if you are using them heavily for long periods? how long is long periods?
Well does the Macbook pro overheat over long periods? It is a very simular design to the iMac which will never be a better cooling solution than a tower pc but given the reliability of the newest laptops now I think we can expect the new iMac to be a tough competitor.

To point out, although the iMac uses more power and produces more heat compared to its Macbook counterpart. The iMac is a better cooling solution. It is built along the vertical axis makings use of convection, it has a larger surface area for radient cooling and uses a bigger single fan and exhaust duct for cpu, gpu cooling, case ventilation and heat extraction. So to answer your question about whether or not the iMac will be able to cope with sustained sessions of use then the answer is yes. If you are using the machine like this every day of the week for 3 years then maybe not. It is in the end of the day goin to take a toll on the components and while it may be designed correctly it does not guarantee it will not overheat. Most likely it might sucom to early failure thought thermal degradation. I suggest if you were to use it like this to either take out apple care through out the life of the machine or buy something suited to 24 hour sustained opperation. It is like turning the wick up on a candle, their is only so much oil to burn. For most users the iMac will suffice thought any task you may throw at it.

As Tucson Allen mentioned the heat pipe is another component which is nearly used in every air cooled computer as it is with the iMac. Through the process he mentioned heat is transferred from one place to another thus playing a crucial part in the cooling system, and while it is going to be effective it is never going to compete with a full tower due to the amount of heat pipes used to cool essential components. This is one of the reasons why laptops and all in ones etc tend to operate at higher temperatures than full tower pc's, and part of the reason why the iMac will have a greater potential to overheat of fail during sustained use.
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Old Nov 10, 2012, 10:16 PM   #23
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For comparison's sake I have correlated imac and mbp. Notice the large capacitors on the imac, cant see if they are solid capacitors or not? They are the white dots across the board, notice the mbp uses a diffident type as the solid cap's normally stick up by 10mm or so. This is one of the advantages of having a bigger package, it also makes it cheaper
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Old Nov 12, 2012, 03:46 AM   #24
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Quote:
Originally Posted by Tucson Allen View Post
You could be right. Your experience with 21.5 and 27 iMacs is extremely helpful. I am assuming that the thin-edge design made a fundamentally changed approach to the convection “chimney” necessary—and that this led to an opportunity for a brilliant improvement in design functionality. With the thin edges the central hump could be formed into a convection engine. Thinking in terms of Boyle’s Law, heating a gas results not merely a temperature change but also involves a pressure change such that if confined in a constant volume, the gas registers an increase in pressure—or, if the gas is free to expand, it will expand with a corresponding temperature drop. This made the thinness a virtue, giving the heated gas a centering bias, and the gas—air—rising to the top, a downward thrust, reenforced by the fan.

The shape of the hump is complex, likened to a teardrop. The point of maximum extension of the back occurs at the vent screen. This means that all flows come together here, the pressured flows acting as thrust. Because of the venting the micro effect is a local pressure drop, reinforcing the complex flow patterns. I judge that the vent size is “tuned” to maximize the flow-through of the enclosure. A vent too large could stultify the desire convection actions.

The expanding heated air does not exit via the intakes in the chin at the bottom. The general tendency of the air inside as its being heated is to rise, creating a partial vacuum at the intakes, helped by their being made of aluminum, an excellent conductor of heat. This causes the air-intake tubes to play a part in the overall chimney effect.

I think it’s an outstanding design. This doesn’t mean that it solves the heat problem of the previous iMacs, but the very quality of the design implies a very knowledgeable designer. Intuitively I register the fact that only one fan is used where two were before is an indication that the other fan isn’t needed—because cooling and venting has been substantially improved. The 5400 rpm HDD in the 21.5 iMac indicates to me that something about the smaller design made the cooler operation of the (more expensive) drive necessary. There is at present no indication that a second fan is necessary. These conjectures lead me to think the 27 iMac is really improved in its heat management. In a way, the 27 iMac has a longer chimney, more room to accelerate the flows. But in the 21.5, which I intend to order, the 5400 rpm drive can’t be far behind with its cooler CPU and GPU.
No doubt these computers were designed by ACTUAL engineers. However, that doesn't at all mean that the engineers were given poor designs. Similarly the designers may very well know a thing or two about engineering, but that doesn't mean that they made the right design decisions in designing.

The iMac has always been a form over function exercise in needless minimalism. If we can shave the total volume down, we will and for no other reason other than to stroke our own ego and make it look externally pretty at the expense of internal practicality and elegance.

That being said, the 21.5" iMac won't have improved in terms of its thermal problems for any other reason other than Apple further neutering it so that the power it outputs finally matches its thermal envelope. That being said, in the 27" iMac, most of these problems haven't been addressed as the only component removed is the optical drive and that machine was made well thinner than the thickness of that drive. These machines won't see thermal improvement from simply rearrangement; they need to use weaker components in order for it to fit and not cause problems. Again, hence the 2.5" 5400RPM drive in lieu of the 3.5" 7200RPM drive. This is also why every video card in the 21.5" iMac is a GT whereas every video card in a 27" iMac is a GTX, a disparity not previously seen between these two iMacs.

If what you want is a computer that will last and be at all utilitarian, the iMac is a terrible machine. If what you want is a computer that is externally gorgeous with no interest in how ugly it is on the inside and what problems may arise from such a design, it'll make you happy. Personally, I'll skip it and make a Hackintosh instead (or just simply use my non-retina 15" MBP as that machine has none of the design failures that plague the iMac).

Quote:
Originally Posted by Tri-stan View Post
For reference:
Image

For anybody reading this the re-designed 2012 iMac is effectively an enhanced MacBook Pro. Same simple design like the mbp the iMac has now got a logic board with cpu, gpu, msata, ram, cooling fan and exhaust outlet. Separate power supply, speakers and hdd. Other components like WiFi, Bluetooth, IR sensor cannot be seen on this image. There is not special cooling system here just an oversized mbp strapped on to an improved cinema display. If the reliability of laptops and the mbp's is anything to go by the new iMac is a more encompassing cooling system that we can expect at least to be on par with the mbps. As long as you are not rendering, encoding or gaming for long sessions all the time then I could expect great things from this revised iMac wth cool running componants at idle..

Some of these ideas for cooling systems, especially the positive charged cooling system looks promising for future designs.
For one, the 27" iMac is not a MacBook Pro, not in terms of design, not in terms of engineering, not in terms of anything. Secondly, that picture you have is of the 27" and not the 21.5". While in terms of components, you're likely right about the 21.5" iMac (save for the CPU), you're completely wrong when it comes to the 27" iMac. Desktop components are very much different from laptop components in terms of how much power they draw, how much heat they generate and how they can be designed when stuffed into such a stupidly thin package.

Quote:
Originally Posted by Siderz View Post
Oh, there's the picture. I was reading this thread earlier wondering where a picture was, and couldn't be bothered to search for one.

Someone said earlier about those black things on the right and left (The things with the large round holes and gaps on the bottom?) I think those are definitely the speakers.

Unless we're talking about the much larger black things on the right and left? Can't think of what those are.



Well, I'll be using it for those things pretty much...except gaming...don't really game much.

I would link to my most recent video (To demonstrate what I regularly do) but I don't want people to go off topic and talk about how bad it is (You need the balls to show it to a forum and then people like to go completely offtopic* and move over to talking about the video).

I think I might get an external Thunderbolt graphics card if the new iMac doesn't handle it that well...I think it should hold out well because it's CUDA certified (So excited to try CUDA).

*I'm now going offtopic...

----------



I'm not entirely sure, I'm not the one t be getting real answers from on this, but I think I remember about a month after the 15" Retina release, there were reports that the cooling sucked.

I wouldn't be surprised (Like people have said earlier) that the iMac will generally be better at cooling anyway.
1. Thunderbolt GPUs don't exist yet. Or rather, ones as powerful as a mid-range graphics card don't exist yet. Thunderbolt only outputs the bandwidth of a PCIe 4x slot; discrete video cards use 8x and 16x. You'd get no real benefit from a Thunderbolt GPU at this point.

2. The 21.5" iMac's cooling will likely improve, while the 27" iMac's cooling will likely worsen. To compare them to a retina is literally comparing apples and oranges; a retina MacBook Pro still uses the same CPUs and GPUs found in its non-retina counter-part, so an increased degree of heat is not surprising.

If you guys don't want it so hot, don't want it so thin.

Quote:
Originally Posted by Tri-stan View Post
Image

For comparison's sake I have correlated imac and mbp. Notice the large capacitors on the imac, cant see if they are solid capacitors or not? They are the white dots across the board, notice the mbp uses a diffident type as the solid cap's normally stick up by 10mm or so. This is one of the advantages of having a bigger package, it also makes it cheaper

?
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Old Nov 12, 2012, 04:24 AM   #25
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I've used my 2009 iMac for heavy photoshop works and games and also 3d (mostly realtime) not so much rendering - and it has done just fine. I doubt heat will be a problem on these models. The 2011 iMac became hot, but I haven't heard much about it shutting down or anything because of this. If it can handle the heat I doubt it will be a problem. from what I read the Ivy Bridge chipset uses less power (meaning less heat) than the Sandy Bridge. So, unless you buy the machine for rendering purposes, I think you will be fine. If you need a render machine or a machine for heavy processor use, buying an iMac is stupid anyway, you pay too much money for the wrong factors of the computer.
If you need a machine that does pretty good all across the board while still looks great the iMac is a great choice. Which is as intended by Apple, a "ALL-IN-ONE" machine for the consumer market - for the generic use not for the specialized use.

Dunno why apple used that extra space they had available for a big fan though But I guess apple knows what they are doing. THe fan could probably be uber large on a 27" .....maybe it is, we havent seen the interior of the 27" yet.
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