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Old 2019-02-16, 20:47   #1
simon389
 
Aug 2013

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Default Overclocking RAM doesn’t seem to do anything

I have DDR 3600 in my Intel 9800X. It’s an 8 core CPU with quad channel memory. I have the CPU stable in Prime 95 LL doublechecks at 4.0Ghz (with AVX512 enabled in Prime95 v. 29.5 build 9).

My question is that the LL seems to crunch at the same speed if the RAM is set at 3400Mhz (underclocked) or 3800Mhz (overclocked). Is this normal? I thought prime 95 was memory bound so having the same iterations/ms despite being clocked 400Mhz higher seems strange to me.
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Old 2019-02-16, 22:48   #2
VBCurtis
 
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It may well be that 3400 quad-channel is enough to feed the CPU; try comparing 3000 to 3400, or 2666 to 3400.
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Old 2019-02-17, 04:36   #3
simon389
 
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Quote:
Originally Posted by VBCurtis View Post
It may well be that 3400 quad-channel is enough to feed the CPU; try comparing 3000 to 3400, or 2666 to 3400.
The 3400 is definitely faster than the 2666. Maybe it is enough. Perhaps I should have gone for the outrageously priced 10-core at $1000 a pop! 🙄
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Old 2019-02-17, 07:09   #4
PhilF
 
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Quote:
Originally Posted by simon389 View Post
The 3400 is definitely faster than the 2666. Maybe it is enough. Perhaps I should have gone for the outrageously priced 10-core at $1000 a pop! 🙄
The i7-9800X has a memory clock speed of 2666, so without overclocking, using memory speeds greater than 2666 will result in very little improvement. The good news, of course, is that you have 4 channels of DDR4-2666 speed. I'm jealous.

The only way to fully utilize your fast memory would be to overclock by lowering the CPU's multiplier then raising the motherboard's clock speed. But with all the problems you have had achieving stability I would recommend you not do that, at least for now.
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Old 2019-02-17, 09:50   #5
M344587487
 
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Depending on the motherboard and RAM setting an OC that sticks may be tricky, I'd triple check that the settings have stuck. In most memory-intensive applications the sub-timings also make a big difference to performance but someone has said it makes little difference for Prime95. Still, if you've ruled out a forgetful mobo and have the time to tinker you may be able to rule out sub-timings by using the same basic ones (tCL, tRCD, tRP, tRAS, https://www.masterslair.com/memory-r...-trcd-trp-tras ) at 3400, 3600 and 3800.
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Old 2019-02-17, 20:58   #6
dcheuk
 
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Hello!

I've compared couple memory options on a 9700k with 4680k fft running ll tests. It's a z390 mb w/ 4 slots and 9700k is dual channel memory, and 8 cores w/o ht, yes it's an i7... It does seem like oc memory doesn't help as much, after like 3600mhz memory becomes noticably more expensive.

- 1 x 8gb (single rank) at 2666mhz cl17 gets me around ~9.5-10ms/it (3 cores, start bottlenecking i presume using 4th core and so on)
- 2 x 8gb (single rank) at 3000mhz cl15 gets me ~6ms/it (4 cores)
- 4 x 8gb (single rank) at 2666mhz cl13 gets me ~5ms/it (5 cores)
- 4 x 8gb (dual rank) at 3400mhz cl17 gets me ~4.8ms/it (5 cores)
- 4 x 16gb (dual rank) at 3600mhz cl17 gets me ~4ms/it (5 cores)
- 2 x 8gb (single rank) at 4600mhz cl19 gets me ~3.8ms/it (6 cores)

I settled with the 4 x 16gb at the end. I am not sure if OC the cpu would help, I never tried, my cpu runs around 55-60F running p95 24/7.

I am really jealous too that you have an 9800x, I thought about going for that setup, but 9800x + x299 + 4 extra memory sticks = higher cost, if I have done that I can only afford like ... integrated graphics for my gpu.

Last fiddled with by dcheuk on 2019-02-17 at 21:00
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