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Old Nov 5, 2012, 12:55 PM   #1
Mac32
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Question iMac 2012/13 version and i5 vs. i7 questions

Hi!

I've decided to go for an 27'' iMac, after several years of using MBPs. However, I'm not sure what is the best choice for me is CPU-wise, the 3.2ghz i5 or the 3.4ghz i7 option.
iMac usage: Internet browsing, iTunes, Sibelius/music composing, gaming, office etc.

As I understand it the i7 is a hotter CPU because of hyperthreading, and could result in a hotter iMac with more fan noise (I'm also going for the Geforce 680MX graphics card). Is there a difference in power consumption between these two CPUs, and could I expect a noticeable difference in temperatures? (Because of the internal HD and the graphics card I would like to have as little CPU heat as possible.)
I've also heard that i7 CPUs can cause stuttering in some games because of the hyperthreading function. Is it easy to disable hyperthreading on your iMac and Mountain Lion OSX?

Thanks! (Getting excited about buying my first iMac, but it's a lot money so I want to get this right.. )

Last edited by Mac32; Nov 5, 2012 at 03:07 PM.
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Old Nov 5, 2012, 01:14 PM   #2
comatory
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Get i5, no benefit from i7 for you.
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Old Nov 5, 2012, 01:25 PM   #3
BrockC
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Quote:
Originally Posted by comatory View Post
Get i5, no benefit from i7 for you.
I get confused quite easily when it comes to these things. Do you care to give a quick rundown of the differences between an i5 & i7 processor? I'm also planning on get an iMac. Thanks!

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Old Nov 5, 2012, 01:28 PM   #4
Mac2133
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Quote:
Originally Posted by comatory View Post
Get i5, no benefit from i7 for you.
Will your advice be the same for someone that does intensive Adobe Photoshop CS6? I do, and process RAW files that are as large as 50-80mb per file. I'm using a 3-year old PC running the 1st Gen Core i7 with 12mb RAM - and the wait time for some photo processing processes seems like forever.
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Old Nov 5, 2012, 01:33 PM   #5
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http://arstechnica.com/gadgets/2012/...e-extra-juice/
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Old Nov 5, 2012, 03:22 PM   #6
comatory
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Quote:
Originally Posted by Mac2133 View Post
Will your advice be the same for someone that does intensive Adobe Photoshop CS6? I do, and process RAW files that are as large as 50-80mb per file. I'm using a 3-year old PC running the 1st Gen Core i7 with 12mb RAM - and the wait time for some photo processing processes seems like forever.
I cant get into the specifics but to find out an answer you might google how Photoshop uses hyperthreading. It is very likely that it does but bear in mind that not all actions will benefit from it.
Processing will definitely be faster but I am not sure what advances were made to hyperthread technology since first generation. Clock speed will matter as well,also the cache od CPU.
It is a pretty complex topic,you should ask around in Adobe forums.
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Old Nov 5, 2012, 03:52 PM   #7
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Thank you so much for the link to that article.
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Old Nov 5, 2012, 06:46 PM   #8
Mac32
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Thanks for the article and the advices, but I'm still a bit unclear on this.
Can I easily disable multithreading on an i7 iMac, and what kind of temperature difference could I expect from going up from the i5 3.2ghz to the i7 3.4ghz? Has anyone experience with both i7 and i5 CPUs (preferably newer ones), and tested them in terms of temperatures?

If anyone could shed some light on this, it would be great. Thanks again..
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Old Nov 5, 2012, 06:53 PM   #9
throAU
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Disabling hyperthreading will not cut temperature.

Unless you are working the machine flat out (in which case, the i7 will complete jobs quite a bit faster), it will run cooler than an i5 due to getting the work done quicker and returning to idle quicker - thus being able to turn parts of itself off and/or reduce clock speed more often. Disabling hyperthreading will simply cripple the CPU and make it run higher clock speeds (thus generating more heat) for longer, and getting your jobs done slower.

The i7 already has pretty advanced power/thermal management inside it so the CPU itself can decide when is appropriate to turn bits of the CPU off, down-clock, etc.

Most people don't need an i7, but worrying about heat and using that as a reason to go for an i5 is just nonsense.


If you encode/transcode video, the hyperthreading on the i7 will enable it to get jobs done much faster.
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Last edited by throAU; Nov 5, 2012 at 07:01 PM.
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Old Nov 5, 2012, 07:33 PM   #10
Mac2133
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Quote:
Originally Posted by throAU View Post
Disabling hyperthreading will not cut temperature.

Unless you are working the machine flat out (in which case, the i7 will complete jobs quite a bit faster), it will run cooler than an i5 due to getting the work done quicker and returning to idle quicker - thus being able to turn parts of itself off and/or reduce clock speed more often. Disabling hyperthreading will simply cripple the CPU and make it run higher clock speeds (thus generating more heat) for longer, and getting your jobs done slower.

The i7 already has pretty advanced power/thermal management inside it so the CPU itself can decide when is appropriate to turn bits of the CPU off, down-clock, etc.

Most people don't need an i7, but worrying about heat and using that as a reason to go for an i5 is just nonsense.


If you encode/transcode video, the hyperthreading on the i7 will enable it to get jobs done much faster.
Thanks for the advise throAU - this makes a lot of sense..
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Old Nov 6, 2012, 04:24 PM   #11
mindquest
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If I planned on running Windows 8 through Fusion do you think this would warrant going up to the i7? I will be running daily automated processes on the windows side so it will be running through out the day.
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Old Nov 6, 2012, 04:53 PM   #12
Mac32
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Quote:
Originally Posted by throAU View Post
Disabling hyperthreading will not cut temperature.

Unless you are working the machine flat out (in which case, the i7 will complete jobs quite a bit faster), it will run cooler than an i5 due to getting the work done quicker and returning to idle quicker - thus being able to turn parts of itself off and/or reduce clock speed more often. Disabling hyperthreading will simply cripple the CPU and make it run higher clock speeds (thus generating more heat) for longer, and getting your jobs done slower.

The i7 already has pretty advanced power/thermal management inside it so the CPU itself can decide when is appropriate to turn bits of the CPU off, down-clock, etc.

Most people don't need an i7, but worrying about heat and using that as a reason to go for an i5 is just nonsense.


If you encode/transcode video, the hyperthreading on the i7 will enable it to get jobs done much faster.
I appreciate you chiming in, thanks! However, after researching this topic around the net, it seems to be a clear perception by people using i7 for overclocking, that hyperthreading will make the CPU run hotter (more parts in the CPU constantly running), often resulting in 10C higher temps. For that reason the i7 is reportedly harder to overclock, and some actually turn off HT to get higher core speeds for gaming. I'm not saying I'm an expert or anything, just reporting what I've read various places.
I am worried about this new thinner design, and the hot running Ivy Bridge (esp. i7) CPUs and a high-end graphics card. I'd rather buy the i7, but if i5 will give less noisy computer when gaming and similar (lower temps = fans have to work less), then I'd go for i5.
I guess the smart thing is to sit on the fence for a few extra weeks, and see how the new iMac turns out.
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