CPU temps – 27 in vs 21.5

WrightBrain

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Original poster
May 30, 2009
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I've done a lot of reading about how on the 27in iMac, the 4.2 Ghz i7 version runs hot and spins up the fan, while the 3.8 Ghz i5 version seems to run cooler.

I was wondering if the 21.5 in iMac with the 3.6 Ghz i7 runs hot or not? Does anyone have any CPU temps to share?

I was basically thinking of going with either the 27in iMac with i5 or the 21.5 in iMac with an i7. The speeds aren't that different and I need it to do Graphic Design, Photoshop and some games.

Thanks
 

MandiMac

macrumors 6502a
Feb 25, 2012
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I was basically thinking of going with either the 27in iMac with i5 or the 21.5 in iMac with an i7. The speeds aren't that different and I need it to do Graphic Design, Photoshop and some games.
For that, you‘d definitely need the best GPU in the 27-incher.
 

WrightBrain

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Original poster
May 30, 2009
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Well, I'd love to buy the 27 inch with i7 and 8 GB video card. But my studio gets really hot in the summer and I've been reading the internal temps of that model go to 100% at times. That will shorten the life of the machine for me.

So I need one that runs cooler. That's why I'm asking if the 21.5 inch with i7 runs cooler.
 

wardie

macrumors 6502
Aug 18, 2008
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That will shorten the life of the machine for me.
You got some evidence behind the shorter life? Anyway that’s discussed on other threads.

I would have thought for you use case the big 27 inch lovely 5k screen is a must? Thus it is choice of i5 or i7.

I have the i7 and of you run it all 8 virtual cores on turbo 4.4GHz then yes the fans spin up and cpu runs around 95-98C and sometimes thermally throttles back frequency.

However personally I’ve found that simply by disabling turbo boost I can run at 4.2GHz on 8 virtual cores constantly max with no extra audible fan and temps down at 90-95C without throttling. Remember the chip is designed to run up to 100C.

But if you are most concerned about the heat output of he machine overall then i5 easy to go I suppose as much less chip wattage if I remember.
 

mikeboss

macrumors 65816
Aug 13, 2009
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switzerland
the lifespan of every electronic part will be shortened when running at higher temps. it's physics, period.

I recently upgraded my iMac (Retina 5K, 27-inch, 2017) from the i5 7500 to i7 7700 (non-K). IMHO, it was not worth it. even though I knew that I will only gain about 10% single-thread performance, I couldn't resist to tinker with it. the i5 with 3.8 GHz also will get pretty hot. only the i5 with 3.4 GHz (i5 7500) and the i5 with 3.5 GHz (i5 7600) will run cool when used at 100% CPU load. better invest the money into the biggest SSD you can afford.

https://www.tomshardware.com/reviews/intel-kaby-lake-core-i7-7700k-i7-7700-i5-7600k-i5-7600,4870-8.html
https://www.tomshardware.com/reviews/intel-kaby-lake-core-i7-7700k-i7-7700-i5-7600k-i5-7600,4870-9.html
https://www.tomshardware.com/reviews/intel-kaby-lake-core-i7-7700k-i7-7700-i5-7600k-i5-7600,4870-10.html
https://www.tomshardware.com/reviews/intel-kaby-lake-core-i7-7700k-i7-7700-i5-7600k-i5-7600,4870-11.html
 
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MandiMac

macrumors 6502a
Feb 25, 2012
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Well, I'd love to buy the 27 inch with i7 and 8 GB video card. But my studio gets really hot in the summer and I've been reading the internal temps of that model go to 100% at times. That will shorten the life of the machine for me.

So I need one that runs cooler. That's why I'm asking if the 21.5 inch with i7 runs cooler.
Just to make it clear, every machine will run hot if you're using both the CPU and the GPU to their fullest in 100 % of the time. This use case is all but very, veeery rare (like BOINC number crunching and scientific DB research work, for instance). If you're using it for Photoshop and games, you a) will need a better GPU and b) won't use 100 % of the CPU/GPU all of the time, just in small bursts. I personally would buy a machine that fits my needs better, and if you're planning to do BOINC or something like that, temperature will be a factor in deciding, yes. But for normal usage, the temps are plenty fine. Apart of what some forum members in here think, Apple ain't stupid. The iMac is idling anyway most of the time (save for raw output like BOINC or Handbrake encoding) which gives it the time needed to cool.

To answer your question, though: Of course a less powerful chip will run cooler. Don't let the naming confuse you: The 21.5 inch machine has the i7 7700 which runs at 3.6 GHz (Turbo boost up to 4.2 GHz, using around 65 watts), whereas the i7 7700K in the 27-incher runs at 4.2 GHz (Turbo boost up to 4.5 GHz, using 91 watts). There is much, much difference between these two processors when it comes to performance. And if used like you described it, you won't run into any issues. Cheers :)
 

Steve121178

macrumors 603
Apr 13, 2010
5,018
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Bedfordshire, UK
I wouldn't worry. Buy Apple Care and if in the highly unlikely scenario that there's an issue, then Apple will sort it out for you.

I've had a late 2012 iMac with the NVIDIA GPU since launch and it's been in some very hot rooms running 24/7 and still going strong after nearly 7 years.
 

WrightBrain

macrumors regular
Original poster
May 30, 2009
134
166
You got some evidence behind the shorter life? Anyway that’s discussed on other threads.

I would have thought for you use case the big 27 inch lovely 5k screen is a must? Thus it is choice of i5 or i7.

I have the i7 and of you run it all 8 virtual cores on turbo 4.4GHz then yes the fans spin up and cpu runs around 95-98C and sometimes thermally throttles back frequency.

However personally I’ve found that simply by disabling turbo boost I can run at 4.2GHz on 8 virtual cores constantly max with no extra audible fan and temps down at 90-95C without throttling. Remember the chip is designed to run up to 100C.

But if you are most concerned about the heat output of he machine overall then i5 easy to go I suppose as much less chip wattage if I remember.
As for proof of a shorter life, no. The mac only came out in 2017. But the actual specs from Intel say 100 degrees is the MAXIMUM the chip should be running at. And PC builders have been giving them crap about the high temperatures. Some have had success delidding them and replacing the cheap thermal paste though.

And actually a large screen isn't a must for me. I like running multiple monitors so going 27 inch would be a downgrade. I'm not certain I can fit a 27 inch and one of my 24 inch monitors on the same desk.

Thanks the CPU temp info does help, though.
 

wardie

macrumors 6502
Aug 18, 2008
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As for proof of a shorter life, no. The mac only came out in 2017. But the actual specs from Intel say 100 degrees is the MAXIMUM the chip should be running at. And PC builders have been giving them crap about the high temperatures. Some have had success delidding them and replacing the cheap thermal paste though.

And actually a large screen isn't a must for me. I like running multiple monitors so going 27 inch would be a downgrade. I'm not certain I can fit a 27 inch and one of my 24 inch monitors on the same desk.

Thanks the CPU temp info does help, though.
Yup the 27 inch is a big beasty. Re shorter life, whilst the physics are the physics I just don’t see a big mass of dead i7 CPUs out there (aside from people over-clocking / modding etc beyond manufacturer spec). Interesting article here:
https://serverfault.com/questions/64956/what-is-the-average-lifespan-of-a-cpu
 

StellarVixen

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Mar 1, 2018
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Bigger case = better airflow, larger surface area, hence better heat dissipation.


At least in theory, but probably true IRL.
 

WrightBrain

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Original poster
May 30, 2009
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Yup the 27 inch is a big beasty. Re shorter life, whilst the physics are the physics I just don’t see a big mass of dead i7 CPUs out there (aside from people over-clocking / modding etc beyond manufacturer spec). Interesting article here:
https://serverfault.com/questions/64956/what-is-the-average-lifespan-of-a-cpu
Yes, but in the same thread it was acknowledged that other parts may die before the CPU like the fan, motherboard, etc. The extra heat puts stress on ALL of the components. And my studio gets hot in the summer – 75 to 80 degrees. I don't want to risk having a system that is always on the verge of getting too hot and throttling back. It's like the six core macbook pro. You never get the full speed because it is constantly throttling back.
 

wardie

macrumors 6502
Aug 18, 2008
348
109
Yes, but in the same thread it was acknowledged that other parts may die before the CPU like the fan, motherboard, etc. The extra heat puts stress on ALL of the components. And my studio gets hot in the summer – 75 to 80 degrees. I don't want to risk having a system that is always on the verge of getting too hot and throttling back. It's like the six core macbook pro. You never get the full speed because it is constantly throttling back.
If you use lots of external monitors and are worried about heat, and want to run CPU intensive long jobs for your work use cases (do you? Wasn’t sure from what you said #1) then maybe you could consider an alternative solution without the thermal constraints of an iMac format. For example a new Mac Mini, or a used MacPro of some sort . Or even a used iMacPro with workstation class CPUs.
 

ABCDEFGHIJKLMNOPQRSTVWXYZ

macrumors newbie
Feb 6, 2019
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i'm no expect so somebody will probably end up correcting something i say.

in my opinion, you should buy the lowest iMac 27" option and upgrade up from there. the lowest iMac 27" has been sold for $1599 in the past (look at slickdeal's history).

ram is easily user upgradable so no comment here.

i'm assuming that all the internal components in the iMac is connected to one cooling source, so it might be a good idea to buy an eGPU because that way, the CPU can get all internal cooling for itself. you lose 20% performance with an eGPU so you shouldn't go anywhere lower than an RTX 2060/Vega 56. the GPU will have better cooling than any option Apple will give you

buy a 7700 or 7700k and upgrade it yourself

while you're in there, you can probably stick an nvme ssd with an adapter into the blade slot. i'm no expert on user upgrade ssd options so you'll have to do some research

after all of this, if everything works, sell the ram, CPU, 1tb HDD, 32gb SSD on ebay or something

now i'll wait for somebody to tell me why this is a bad idea
 

MandiMac

macrumors 6502a
Feb 25, 2012
670
319
i'm no expect so somebody will probably end up correcting something i say.

in my opinion, you should buy the lowest iMac 27" option and upgrade up from there. the lowest iMac 27" has been sold for $1599 in the past (look at slickdeal's history).

ram is easily user upgradable so no comment here.

i'm assuming that all the internal components in the iMac is connected to one cooling source, so it might be a good idea to buy an eGPU because that way, the CPU can get all internal cooling for itself. you lose 20% performance with an eGPU so you shouldn't go anywhere lower than an RTX 2060/Vega 56. the GPU will have better cooling than any option Apple will give you

buy a 7700 or 7700k and upgrade it yourself

while you're in there, you can probably stick an nvme ssd with an adapter into the blade slot. i'm no expert on user upgrade ssd options so you'll have to do some research

after all of this, if everything works, sell the ram, CPU, 1tb HDD, 32gb SSD on ebay or something

now i'll wait for somebody to tell me why this is a bad idea
Because it completely defeats the idea of buying something and using it right away, and the idea of an all-in-one with it, too.
 

Porkchop Sandwich

macrumors regular
Feb 3, 2017
243
133
I don’t perform intensive tasks for music production or photo/video but, I do push my iMac (21.5” i7) pretty hard for intermittent sessions involving multiple office applications and multiple screens of said applications simultaneously. Sometimes a little CAD work, but not much. Quite often I’ll drive the LG5K while working as well.

I do basic things with video/photos but that’s typically limited to trimmings vids and modest photo edits using Apple’s native apps (e.g., cropping, overlaying text, convert to pdf, etc).

Music production: as much as I want to, I simply never do anything with my iMac because I’ve never taken the time to sort any of it out (learn). *I do have multiple amps, some rack effects, and basic recording equipment - just not integrated into the mac environment or pro tools.

Although it’s apples/oranges to a large extent, I also have a 27” 2010 iMac w/an i7. No matter the environment, the 27” has always run quite warm but it never misses a beat. Plus it has, indeed, been used in environments such as the environment you have described for long periods of time. The current 21.5 w/i7 and inherent heat??, err, not so much. I haven’t any measured numbers for you but it seems to run rather cool. It purrs right along and has proven to be a really nice computer that doesn’t hiccup at all. I can’t say it’s persistently run in an environment where ambient is any more than say 72’ish but, there are times that I run it in a room with a wood stove and that sucker will take ambient up to a wonderfully blissful 80+ in the winter months. During those times, I can’t say I’ve noticed much, if any difference at all in the way of extra heat or reduced performance using the computer. Once again, I’m sorry I haven’t any actual temps to share, and I can’t offer you real-world certainty that the 21.5 i7 wouldn’t be problematic in a persistent environment, but I highly doubt it. It’s been a kick ass computer for me. I think many here would surmise I’m not a “pro” user..but..lol, whatever.

FWIW – if an iMac, any iMac would be a consideration for you; the 21, sounds like a good choice.

I’d also caution you not to fall victim to the 27/21 bs that seems to run overtly rampant on this site.

The 2017 21.5” iMac is a stellar computer.
 

WrightBrain

macrumors regular
Original poster
May 30, 2009
134
166
If you use lots of external monitors and are worried about heat, and want to run CPU intensive long jobs for your work use cases (do you? Wasn’t sure from what you said #1) then maybe you could consider an alternative solution without the thermal constraints of an iMac format. For example a new Mac Mini, or a used MacPro of some sort . Or even a used iMacPro with workstation class CPUs.
Well I DO run one external monitor. But I need to be able to run High Sierra or Mojave. So a mac that is too old is out.

I'm leaning towards the 27 in iMac with 3.8 i5 and 8 GB 580. I'm thinking I can disable the Turbo Boost if it gets too hot. All I want is a machine that performs well and will last 5 or so years. Top performance isn't an issue as anything will be better than what I have.

I run the Adobe Suite – both CS and CC. I need to upgrade my OS to run CC 2019 and my machine is over 10 years old. I do some games but mostly do my gaming on consoles. No vid and no music. I also just hate how expensive everything is. By the time I pay this off, I will need a new one. AND my wife will need a new iMac in a year or two – same usage profile.

Does anyone have any experience with the i5 with Turbo on and off?
[doublepost=1551633753][/doublepost]
i'm no expect so somebody will probably end up correcting something i say.

in my opinion, you should buy the lowest iMac 27" option and upgrade up from there. the lowest iMac 27" has been sold for $1599 in the past (look at slickdeal's history).

ram is easily user upgradable so no comment here.

i'm assuming that all the internal components in the iMac is connected to one cooling source, so it might be a good idea to buy an eGPU because that way, the CPU can get all internal cooling for itself. you lose 20% performance with an eGPU so you shouldn't go anywhere lower than an RTX 2060/Vega 56. the GPU will have better cooling than any option Apple will give you

buy a 7700 or 7700k and upgrade it yourself

while you're in there, you can probably stick an nvme ssd with an adapter into the blade slot. i'm no expert on user upgrade ssd options so you'll have to do some research

after all of this, if everything works, sell the ram, CPU, 1tb HDD, 32gb SSD on ebay or something

now i'll wait for somebody to tell me why this is a bad idea
I'm too Chicken S to pull a 2017 iMac apart. I HAVE pulled a 2010 iMac with the magnets apart but munged up the flat ribbon cable. Luckily the video card on that was toast anyway, so it wasn't a working machine. And I got it for free.
 

wardie

macrumors 6502
Aug 18, 2008
348
109
Well I DO run one external monitor. But I need to be able to run High Sierra or Mojave. So a mac that is too old is out.

I'm leaning towards the 27 in iMac with 3.8 i5 and 8 GB 580. I'm thinking I can disable the Turbo Boost if it gets too hot. All I want is a machine that performs well and will last 5 or so years. Top performance isn't an issue as anything will be better than what I have.

I run the Adobe Suite – both CS and CC. I need to upgrade my OS to run CC 2019 and my machine is over 10 years old. I do some games but mostly do my gaming on consoles. No vid and no music. I also just hate how expensive everything is. By the time I pay this off, I will need a new one. AND my wife will need a new iMac in a year or two – same usage profile.

Does anyone have any experience with the i5 with Turbo on and off?
[doublepost=1551633753][/doublepost]
I'm too Chicken S to pull a 2017 iMac apart. I HAVE pulled a 2010 iMac with the magnets apart but munged up the flat ribbon cable. Luckily the video card on that was toast anyway, so it wasn't a working machine. And I got it for free.
Does sound like you have have your sweet spot there. Good luck!

On the macOS level, I just got a very old late 2009 iMac 27inch i7 second hand and have upgraded it (SDD,RAM). But even that is running High Sierra. I would also say it feels (to the touch) way hotter than my 2017 5k i7. Good cheap alternative but I doubt it meets your graphics needs, and only has USB2/FW800 era ports. But good for what I need for the family.
 
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bbnck

macrumors 6502a
Mar 19, 2009
586
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I use my 27-inch iMac for software development (2017, i5-7500). During a busy work day I've never seen the CPU temperatures exceed 65℃. Contrast this with my work 13-inch MacBook Pro (2017, i5-7360U) which I've seen reach 100℃ several times.
 

JesseJohnston

macrumors newbie
Jun 16, 2019
1
0
Well I DO run one external monitor. But I need to be able to run High Sierra or Mojave. So a mac that is too old is out.

I'm leaning towards the 27 in iMac with 3.8 i5 and 8 GB 580. I'm thinking I can disable the Turbo Boost if it gets too hot. All I want is a machine that performs well and will last 5 or so years. Top performance isn't an issue as anything will be better than what I have.

I run the Adobe Suite – both CS and CC. I need to upgrade my OS to run CC 2019 and my machine is over 10 years old. I do some games but mostly do my gaming on consoles. No vid and no music. I also just hate how expensive everything is. By the time I pay this off, I will need a new one. AND my wife will need a new iMac in a year or two – same usage profile.

Does anyone have any experience with the i5 with Turbo on and off?
[doublepost=1551633753][/doublepost]
I'm too Chicken S to pull a 2017 iMac apart. I HAVE pulled a 2010 iMac with the magnets apart but munged up the flat ribbon cable. Luckily the video card on that was toast anyway, so it wasn't a working machine. And I got it for free.
I just DIY upgraded a 21.5" 2017 iMac with i5-7500 to a i7-7700 (also did a SSD upgrade and RAM upgrade), and already I am noticing the fans running a fair bit more, with a stable temp of around 60C for medial tasks. With only the single fan in the 21.5", I'm hesitant to think that when I work the CPU it will just crank the fan and be audible in the room I'm working in, which is really not ideal.
 

macdudesir

macrumors 6502
Jan 16, 2011
357
76
Blacksburg, VA
The heat won't hurt your iMac. Apple aren't fools, they know how to manage heat. Your CPU is safe to operate up to 100C and if it goes over that (it won't) it will protect itself. Further, Apple is smart enough to monitor other component temperatures as well which means that it will also protect the other components you seem so worried about.

So basically, get the iMac you need and stop worrying about things that engineers are paid a lot of money to worry about for you. They have it sorted out. No amount of heat will bring the lifespan of your machine to under 5 years. Maybe it does affect longevity, but we're talking 15 vs 17 years...it will long be obsolete before any damage you're thinking of manifests itself.
 
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