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Hyperthreading on i7

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Bartos88

macrumors member
Original poster
Apr 8, 2011
35
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Hi, I am currently deciding which 27" imac to get. With student discount the i5 3.1GHz would be 1.670,76 euro. For 1.846,88 (176 euro more) I could get the i7. I read that only the i7 has hyperthreading. Could someone explain in layman's terms what that means? Would this only give an advantage when using specialized applications that are optimized for quad-core use, or does hyperthreading also increase performance on applications that are not made for multi-core use?

Also, if I choose not to get the i7. Would it make more sense to go with the cheaper 2.7GHz i5 because of the higher turbo-boost which brings the performance closer to the 3.1 i5. I'm probably not gonna play much games, so the 512MB should be enough for me, but maybe for future-proofing/resale-value it would be wiser to get the 1GB?

Any info/advice would be appreciated :)
 
Hyper threading is only useful in multithreaded applications that are used for things like video or photo processing or 3D rendering. In a general sense, hyper threading is useful when multiple threads of execution are similar enough to each other. This is obviously true enough when applications are designed to make use of hyper threading. It will not be useful when doing multiple different things (e.g. running a lot of different applications at once).

As for video RAM, go with 1GB... would be a good idea if you ever decide to plug in a second monitor to your machine.
 
Hyperthreading is the latest name for an Intel technology that effectively allows a single physical core to run as two virtual cores. So in the current iMac range the i5 processors have 4 physical cores and can run 4 threads in parallel. The i7 processores have 4 physical cores but can run 8 threads in parallel thanks to hyperthreading.

So Hyperthreading only really offers an advantage with applications that are designed to run on multiple cores. Unfortunately things aren't entirely that simple as there's also the slightly faster clock speed of the i7 and Turbo Boost to consider.

Turbo Boost effectively lets a processor speed up when it's not using all of its cores by 'shutting off' the cores that aren't in use. Off the top of my head the i5 3.1Ghz can Turbo Boost to 3.4Ghz while the i7 3.4Ghz can run to 3.8Ghz. The real world difference is relatively small but can be worth a couple of frames a second in a game or a few seconds off a benchmark.

Hope that helps a bit, if there's anything there that's not clear just ask.
 
smiddlehurst said:
Turbo Boost effectively lets a processor speed up when it's not using all of its cores by 'shutting off' the cores that aren't in use. Off the top of my head the i5 3.1Ghz can Turbo Boost to 3.4Ghz while the i7 3.4Ghz can run to 3.8Ghz. The real world difference is relatively small but can be worth a couple of frames a second in a game or a few seconds off a benchmark.
Click to expand...

Incorrect. Turbo boost is "dynamic overclocking". Depending on the current number of cores being used and if additional processing power is required, the CPU will slowly increase the clock rate for the currently active cores. It'll do this incrementally until the thermal operating limit of the processor is reached.
 
Ok thanks for the info guys. I guess the main thing to take away from your info is that hyperthreading would do relatively little for me. This leaves the slightly faster clockspeed (and therefore slightly higher turboboost max) as the deciding factor for the i7.

I think I'm gonna go with the 3.1 i5, which should be a huge improvement for me seeing as i'm coming from a 2008 macbook with 2GHz C2D en 2GB of ram :p
 
Vylen said:
Incorrect. Turbo boost is "dynamic overclocking". Depending on the current number of cores being used and if additional processing power is required, the CPU will slowly increase the clock rate for the currently active cores. It'll do this incrementally until the thermal operating limit of the processor is reached.
Click to expand...

Umm, isn't that pretty much exactly what I described in my OP? Albeit I didn't use the phrase "dynamic overclocking".
 
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