i9-7900X or 7920X? I'm having trouble understanding clock speeds.

[wockawocka]

Hiya.

I'm stuck between two chips.

7900X - 3.3ghz base. 4.3Ghz turbo
7920X - 2.9ghz base. 4.3Ghz turbo

For me, the higher the clock speed the better. But seeing as each chip has equal turbo boost. Shouldn't I be getting the faster base one?

I don't need more than 20 threads tbh. But I do need a zippy chip. With Intel's turbo boost, should I disable Turbo Boost 3 as I've read online it doesn't boost all the cores where Turbo Boost 2 will? Or is it just that only a couple of cores (the best) will be maxed out while the others are at Turbo boost 2 level?

TIA!

[Korth]

Summarized list of LGA2066 CPUs:
https://en.wikipedia.org/wiki/LGA_2066

i9-7900X has 10C/20T, 3.3GHz/4.3GHz/4.5GHz, 10MB L2, 13.75MB L3, $1000
i9-7920X has 12C/24T, 2.9GHz/4.3GHz/4.4GHz, 12MB L2, 16.5MB L3, $1200

More Cores/Threads means faster at multithreading, more things in parallel. Only useful when you actually run many complex tasks simultaneously, multiple VMs, etc.
Common stuff like browsing, Facebook, Netflix/Youtube, etc will only use a single thread for each window you open, another for the Windows operating system itself, and perhaps one or two others if you're running complex programs in background. Heavy games usually run only 1-2 threads, sometimes 3-4, a few titles will use a few more if they're available. A 4C/8T CPU is actually plenty for 99% of "normal users" and 90% of "power users" or gamers, although (with Ryzen and Coffee Lake) 6C/12T is now starting to become the new "high end mainstream" baseline.
The 12C/24T part will not be faster than the 10C/20T part unless you can actually keep all the cores busy.

The three speed ratings are base clock (standard operating frequency), Turbo/Boost clock (the processor will ramp itself up to this speed when needed AND when sufficient power is available AND when within thermal limits), and Max Turbo/Boost clock (the processor can ramp some cores up to this maximum when needed AND when sufficient power is available AND when within thermal limits).
Faster clock speeds are always useful no matter what you're doing, no matter how many (or not many) cores/threads are in demand.
A good motherboard, a good PSU, and a good CPU cooler all work to extend power and thermal limits so the CPU can operate at Turbo/Boost levels more often.
The CPUs with higher TDP Wattages consume more power and produce more heat, they require more aggressive cooling to keep temps down (and Turbo clocks up).

L2 and L3 caches increase performance by storing data inside the CPU (and each CPU core) so it doesn't need to move to and from off-CPU (RAM, SSD, etc) as much.
More cache is always better, especially for core-intensive multitasking, but it has much less impact on overall performance than raw clock speeds.

The fastest LGA2066 CPU currently on market is actually the i9-7820X, 8C/16T, 3.6GHz/4.3GHz/4.5GHz, 8MB L2, 11MB L3, $600

The "simpler" CPUs with fewer cores, less caches, etc, tend to be easier to overclock. Less complexity to work around, less chance of a single "weak" subcomponent bottlenecking performances (determining the maximum limits) for the whole silicon package.

If you want a "zippy" chip then you'd be better off with an Intel Z270/i7-7700K platform right now or an Intel Z370/i7-8700K platform in a few weeks (just released but actual availability seems nonexistent). Or an AMD Z370/R7-1800X or an AMD X399/TR-1900X.

[wockawocka]

Thanks Korth, I appreciate the insight. Thanks for switching me on to the 8700k, I was also about to build a new pc for my wife based on the 7700k but the former chip and chipset are much better for a fraction more outlay.

Thanks again!

[Tobarus]

Very insightful. I'm in pretty much the exact same situation (deciding between 7900x or 7920x for my Rampage VI extreme, which is sitting very lonely)

I'm using my PC mainly for gaming, but also and maybe more importantly, for Adobe products such as Photoshop, Premier Pro, After Effects, encoding video etc. As far as I understand, gaming is obviously most heavely reliant on clock speeds, while Adobe runs faster on higher clocks speeds, with a slight emphasis or cores/threads (more so than many games), but does not benefit from huge core counts (well, make use of).

Korth, if price did not matter, which would you choose strictly only between the 7900x or 7920x based on the above - just considering pure performance and not price?

...And to throw a wrench into things, while this is subjective, now considering price, what if you could get the 7900x for $930 USD, and the 7920x for $890 USD? Through some "connections" this is actually what I'd be paying. Would the fact that the 7920x is actually $40 cheaper than the 7900x (yes, sounds strange) make it a better buy? Or would the all out clock speeds of the 7900x still make it faster/better?

On an important side note, I'm liquid cooling everything, and my current 5960x has never gone above 40-something degrees C, running at 4.2ghz. I guess what I'm "trying" to say is that I don't think thermals, nor available current from the psu will be a problem, so the turbo boost should be readily available. Maybe this levels the playing field between the 7900x and 7920x?

Many thanks for the insight, very much appreciated!

Korth wrote:
Summarized list of LGA2066 CPUs:
https://en.wikipedia.org/wiki/LGA_2066

i9-7900X has 10C/20T, 3.3GHz/4.3GHz/4.5GHz, 10MB L2, 13.75MB L3, $1000
i9-7920X has 12C/24T, 2.9GHz/4.3GHz/4.4GHz, 12MB L2, 16.5MB L3, $1200

More Cores/Threads means faster at multithreading, more things in parallel. Only useful when you actually run many complex tasks simultaneously, multiple VMs, etc.
Common stuff like browsing, Facebook, Netflix/Youtube, etc will only use a single thread for each window you open, another for the Windows operating system itself, and perhaps one or two others if you're running complex programs in background. Heavy games usually run only 1-2 threads, sometimes 3-4, a few titles will use a few more if they're available. A 4C/8T CPU is actually plenty for 99% of "normal users" and 90% of "power users" or gamers, although (with Ryzen and Coffee Lake) 6C/12T is now starting to become the new "high end mainstream" baseline.
The 12C/24T part will not be faster than the 10C/20T part unless you can actually keep all the cores busy.

The three speed ratings are base clock (standard operating frequency), Turbo/Boost clock (the processor will ramp itself up to this speed when needed AND when sufficient power is available AND when within thermal limits), and Max Turbo/Boost clock (the processor can ramp some cores up to this maximum when needed AND when sufficient power is available AND when within thermal limits).
Faster clock speeds are always useful no matter what you're doing, no matter how many (or not many) cores/threads are in demand.
A good motherboard, a good PSU, and a good CPU cooler all work to extend power and thermal limits so the CPU can operate at Turbo/Boost levels more often.
The CPUs with higher TDP Wattages consume more power and produce more heat, they require more aggressive cooling to keep temps down (and Turbo clocks up).

L2 and L3 caches increase performance by storing data inside the CPU (and each CPU core) so it doesn't need to move to and from off-CPU (RAM, SSD, etc) as much.
More cache is always better, especially for core-intensive multitasking, but it has much less impact on overall performance than raw clock speeds.

The fastest LGA2066 CPU currently on market is actually the i9-7820X, 8C/16T, 3.6GHz/4.3GHz/4.5GHz, 8MB L2, 11MB L3, $600

The "simpler" CPUs with fewer cores, less caches, etc, tend to be easier to overclock. Less complexity to work around, less chance of a single "weak" subcomponent bottlenecking performances (determining the maximum limits) for the whole silicon package.

If you want a "zippy" chip then you'd be better off with an Intel Z270/i7-7700K platform right now or an Intel Z370/i7-8700K platform in a few weeks (just released but actual availability seems nonexistent). Or an AMD Z370/R7-1800X or an AMD X399/TR-1900X.

[JustinThyme]

Tobarus wrote:
Very insightful. I'm in pretty much the exact same situation (deciding between 7900x or 7920x for my Rampage VI extreme, which is sitting very lonely)

I'm using my PC mainly for gaming, but also and maybe more importantly, for Adobe products such as Photoshop, Premier Pro, After Effects, encoding video etc. As far as I understand, gaming is obviously most heavely reliant on clock speeds, while Adobe runs faster on higher clocks speeds, with a slight emphasis or cores/threads (more so than many games), but does not benefit from huge core counts (well, make use of).

Korth, if price did not matter, which would you choose strictly only between the 7900x or 7920x based on the above - just considering pure performance and not price?

...And to throw a wrench into things, while this is subjective, now considering price, what if you could get the 7900x for $930 USD, and the 7920x for $890 USD? Through some "connections" this is actually what I'd be paying. Would the fact that the 7920x is actually $40 cheaper than the 7900x (yes, sounds strange) make it a better buy? Or would the all out clock speeds of the 7900x still make it faster/better?

On an important side note, I'm liquid cooling everything, and my current 5960x has never gone above 40-something degrees C, running at 4.2ghz. I guess what I'm "trying" to say is that I don't think thermals, nor available current from the psu will be a problem, so the turbo boost should be readily available. Maybe this levels the playing field between the 7900x and 7920x?

Many thanks for the insight, very much appreciated!

A few things to consider in comparison to these two chips.

Firstly the turbos speeds only reference two cores so dont pay much attentiion to that.

Lets just throw cost out the window, if you have already bought the rest of the components the cost differenc of the two chips is a moot point.

Either chip requires serious cooling. A 3 FAN AIO is bare minimum and will not support a decent overclock on either chip. Consider this and incorporate a custom loop into your build.

Now considering all of this

7920 will come out ahead with all things equal being both at stock everything by about 5%.

It will remain ahead in multicore tasks into over clocking.

It will fall behind for anything not using all the cores, particilary gaming and daily use.

[Korth]

I agree, it's foolish not to buy CFL Z370/i7-8700K instead of KBL or SKL.

Unless the KBL/SKL platform costs substantially less. Remember that just a month ago KBL was king, just a year ago SKL was king. There's still plenty of truly excellent motherboards and kits for these platforms, and Z170/Z270 offered all the same general hardware as Z370 except maybe a few fancy new bells and whistles you may never use.
I'd price out a CFL platform then compare vs the prices and features of KBL/SKL platforms, might waste time, might save money.

SKL i7-6700K 4C/8T, 4.0GHz/4.0GHz/4.2GHz, 8MB, DDR4-2133, 91W
KBL i7-7700K 4C/8T, 4.2GHz/4.4GHz/4.5GHz, 8MB, DDR4-2400, 91W
CFL i7-8700K 6C/12T, 3.7GHz/4.3GHz/4.7GHz, 12MB, DDR4-2666, 95W
(Base clock, all-core Turbo, single-core Turbo)

Why 6C/12T vs 4C/8T isn't very impressive (yet):
https://www.youtube.com/watch?v=bPvgoQ64E08&t=2s