Why does older but faster CPUs bottleneck newer GPUs?

[johnhenrylim12]

I am planning to upgrade to a newer GPU, and wherever I searched, newer CPUs are always recommended. What I do not understand however is that some of these newer CPUs have lower clock speeds than my existing CPU. As far as I know, CPU clock speed is the main factor for GPU bottleneck, so why would a newer but slower CPU be better than an older but faster one? I cannot seem to find the answer anywhere.

 

[Dunlop0078]

Clock speed is a factor but it does not tell nearly the whole story. CPU IPC (instructions per clock) is another which basically means how many calculations a CPU can perform at a given clock speed. A 8th gen i7 can perform more calculations at say 3.5ghz than a 2nd gen i7 could. So if you took a single core out of an 8700k and a single core out of a 2700k at the same clock speed the 8700k core would perform much better than the 2700k core. There are other factors besdies that as well.

If I knew what CPU you were talking about I could provide a more specific answer.

 

[Wolfshadw]

Think of it like gears in a car.

5000RPMs in first gear isn't going to get you far, but 3000RPMs in second gear will.
Now swap RPMs for GHz and gears for CPU generations.

Perhaps, overly simplistic, but that's the general idea. Newer generations of CPUs simply perform better at lower GHz. Of course there are newer instruction sets and better thermal designs for the newer processors as well which also improve performance.

-Wolf sends

 

[nobspls]

Older faster CPUs do not bottleneck. Why do you think Tom's testing the RTX2080ti with the 7700K? See:
https://www.tomshardware.com/reviews/nvidia-geforce-rtx-2080-ti-founders-edition,5805.html
"
Nvidia’s latest and greatest will no doubt be found in one of the many high-end platforms now available from AMD and Intel. Our graphics station still employs an MSI Z170 Gaming M7 motherboard with an Intel Core i7-7700K CPU at 4.2 GHz, though. The processor is complemented by G.Skill’s F4-3000C15Q-16GRR memory kit. Crucial’s MX200 SSD remains, joined by a 1.4TB Intel DC P3700 loaded down with games.
"

The question remain is you need to show us that older faster CPU you have in mind.

I can tell you my old i7-2600K does NOT bottleneck my GTX1060, and does better than my newer slower Ryzen 5 1600 using the same GTX1060, even with both OC-ed to 4.0 Ghz, and to top it off, my old i7-2600K can clock to 4.2 GHz, where as the R5 1600 won't run stable past 4.0 Ghz.

 

[johnhenrylim12]

Clock speed is a factor but it does not tell nearly the whole story. CPU IPC (instructions per clock) is another which basically means how many calculations a CPU can perform at a given clock speed. A 8th gen i7 can perform more calculations at say 3.5ghz than a 2nd gen i7 could. So if you took a single core out of an 8700k and a single core out of a 2700k at the same clock speed the 8700k core would perform much better than the 2700k core. There are other factors besdies that as well.

If I knew what CPU you were talking about I could provide a more specific answer.

Thank you. I am using the i5 4690k and would like to upgrade to a GTX 1080Ti (or maybe even an RTX 2070).

 

[nobspls]

I think you are looking at 8700K or bust. See:
https://www.techspot.com/review/1655-core-i7-8700k-vs-ryzen-7-2700x/page8.html

Otherwise your old haswelli5-4690k will be just as good and other out there.