Newbie Processor Question

jonatious

macrumors member
Original poster
Sep 29, 2016
45
23
So the i9 9900K processor has 8 cores and can run at 3.6GHz on 8 cores. At 6 cores the per clock speed is 4.7k which would give a total speed of 28.2k. With 7 cores, the overall speed reduces to 25.2k and with 8 cores at 3.6GHz, the speed is 28.8k?

I don't get it, so when my application starts to use 7 cores, the overall speed falls? and when using all cores it is almost the same as 6 cores? Then what is the point of the 7th and 8th cores on the processor?

 

kaintxu

macrumors regular
Jul 9, 2018
167
73
Edinburgh
So the i9 9900K processor has 8 cores and can run at 3.6GHz on 8 cores. At 6 cores the per clock speed is 4.7k which would give a total speed of 28.2k. With 7 cores, the overall speed reduces to 25.2k and with 8 cores at 3.6GHz, the speed is 28.8k?

I don't get it, so when my application starts to use 7 cores, the overall speed falls? and when using all cores it is almost the same as 6 cores? Then what is the point of the 7th and 8th cores on the processor?


When intel designs the processor, is not thinking that is going to be put in an AIO with poor cooling. Intel designs their processor trying to achieve better performance (and hopefully stability), but it's not their fault how other manufacturer use them in their AIO.

Now, now every task you ise is going to use all 8 cores, and on anything that is going to be using 1-6 you are going to be ahead of the curse. Also, if something needs 8 cores, even is they are each not much faster than a 6 core, you are actually doing the task with 8 cores which an I5 would not be able to
 

jonatious

macrumors member
Original poster
Sep 29, 2016
45
23
When intel designs the processor, is not thinking that is going to be put in an AIO with poor cooling. Intel designs their processor trying to achieve better performance (and hopefully stability), but it's not their fault how other manufacturer use them in their AIO.

Now, now every task you ise is going to use all 8 cores, and on anything that is going to be using 1-6 you are going to be ahead of the curse. Also, if something needs 8 cores, even is they are each not much faster than a 6 core, you are actually doing the task with 8 cores which an I5 would not be able to
Gotcha, thanks :)
 

keysofanxiety

macrumors G3
Nov 23, 2011
9,517
24,546
They slow down due to additional heat that the cores produce. However clockspeed doesn't do all that much compared to software optimisation and whether the software can utilise the cores.

It used to be more important, but we're talking about multicore CPUs and only fractional reductions in clockspeed. You'll generally get more benefit when all cores are being used.

I'd recommend watching the Megahertz myth Apple video. It's an older video filmed on a potato and uploaded using a cup and string, but the fundamentals are still applicable and they explain it really well:

 

SkiHound2

macrumors regular
Jul 15, 2018
164
111
There's lots of concern and angst about how hot the i9 will run and how much it's being throttled by the iMacs cooling system. The chip is rated as a 95watt but if heavily loaded it was use more than 95 watts and generate more heat. It seems to be limited to 95W in the new iMac. None of the cpus will ever sustain maximum turbo speeds on all cores for extended periods of time. Perhaps if they are water cooled? You can't really equate something like 2 cores at 4ghz and 4 cores at 2ghz. With some things the former may be faster and for other things the latter may be faster (I'm kind of using these numbers only to illustrate my point). Some software is written to exploit many cores and hyperthreading. Other software doesn't really benefit much from more cores. Most current games don't make effective use of multiple cores and maximum ghz becomes more important. Other programs, like video rendering software may exploit as many cores as are available. More cores means the cpu can do more things at the same time if it's being asked to do more things at the same time. Hyperthreading provides logical cores so that if cores aren't being maxed out, they can do two less demanding tasks at the same time. If you look at benchmark tests for some of the high end workstation cpus (like Xeons, or AMD Threadrippers) you'll find they don't really perform that in single core tasks because the clock speed is relatively slow. But they are much faster in multicore benchmarks. In the graph above you'll see that the i9 can only hit 5ghz on 2 cores when wattage is not restricted. Only 1 core if wattage is limited to 95. Unless you're doing some really cpu intensive tasks you'd never notice the difference between the i9 limited to 95watts and the i9 unrestricted. I'm still using a 2012 Mac Mini with i7 4 core 2.6ghz. By current standards it's pretty sluggish. But it still does all of the basics (email, web browsing, playing videos (I don't think it would handle 4k but it streams fine on a 1440p monitor), music, word processing, etc. It wouldn't play modern games. It might take years to render video, etc. I do photo editing and it can get a bit bogged down doing some tasks so I'm feeling it's time to upgrade.