Question Unstable at 4133 mhz but not 4000 mhz?

Mar 22, 2019
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I've got a fairly new PC (6 months old) with the following spec:

Intel I9 9900k
Xorus Xtreme Z399 motherboard
4 x 8gb GSkill 4133mhz memory
850W platinum modular power supply

With the machine running on the default XMP profile (4133 mhz) I see errors in Memtest86 tests. If I take that down to 4000mhz in the bios it's perfectly happy. Fairly sure it should be stable at 4133 but it isn't - can anyone offer suggestions why this may be? I considered that I may need to nudge up the ram voltage a little but surprised it doesn't work 'out of the box'.

Cheers,
 

TJ Hooker

Illustrious
Herald
Again, what was the exact kit?

RAM is only guaranteed to work together when bought as a single kit, if you combine different kits (even the exact same model numbers) there can be issues. Also, running 4 sticks is generally harder than 2.

Those two things, combined with the fact that 4000+ MHz is very fast (and thus difficult to run) makes in unsurprising that you're having issues.
 
Mar 22, 2019
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Again, what was the exact kit?

RAM is only guaranteed to work together when bought as a single kit, if you combine different kits (even the exact same model numbers) there can be issues. Also, running 4 sticks is generally harder than 2.

Those two things, combined with the fact that 4000+ MHz is very fast (and thus difficult to run) makes in unsurprising that you're having issues.
The exact kit was G.Skill Trident Z RGB 16GB Kit DDR4 4133MHz RAM (x 2). See, my simplistic view of this is that if a product advertises that it can run at a certain speed (4133mhz in this case) then it should be capable of doing just that. Perhaps using it with another identical kit IS outside of their scope of functionality - but id say the majority of people would assume that it'll work. I mean, when you buy car tyres of the same type - you don't expect to skid off the road because the back two and the front two don't play well together, despite being identical!

All that being said, so far it's quite happy running at 4000mhz which is fine too really. :)
 
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Gam3r01

Titan
Moderator
The exact kit was G.Skill Trident Z RGB 16GB Kit DDR4 4133MHz RAM (x 2). See, my simplistic view of this is that if a product advertises that it can run at a certain speed (4133mhz in this case) then it should be capable of doing just that. Perhaps using it with another identical kit IS outside of their scope of functionality - but id say the majority of people would assume that it'll work. I mean, when you buy car tyres of the same type - you don't expect to skid off the road because the back two and the front two don't play well together, despite being identical!
Except mixing RAM kits is a bit more complex than tires, think more along the lines of a kidney transplant.
You could have two that are a perfect match for you individually, but if you take both at the same time youll probably be okay, but also maybe not.

For the most part, the assumption that RAM works outside of paired kits is fine for most users, as it does indeed work most times.
Then again, most people assuming kits work that way also arent trying to push 4133MHz on their kits.

Test the kits in the pairs they were sold in, 16GB at a time. If they pass on their own, then you know the mixing is the issue.
 
Mar 22, 2019
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I didn't really consider that attempting to run memory at it's advertised speed would be classed as overclocking it. I mean, I get that the factory non-xmp speed is 2133mhz but why even advertise it as 4133 unless you're confident it'll work at that? You know what I mean?

Anyway thanks for the input - i'll likely just keep it at 4000mhz and see how it runs. To be fair, it was very occasional crashing anyway but according to Memtest86 it seems happier at 4k.
 
Mar 22, 2019
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Test the kits in the pairs they were sold in, 16GB at a time. If they pass on their own, then you know the mixing is the issue.
Actually that's a good idea. If it were easy to add/remove the memory I'd probably do that just out of interest but they are underneath my CPU heatsink and I'm ultimately pretty lazy.
 
I didn't really consider that attempting to run memory at it's advertised speed would be classed as overclocking it.
It's not. To use your tire analogy, this is like complaining that after putting Z-rated tires on your Hyundai, it still cannot go the 150mph the tires are rated for.

The memory can run at 4133 so long as you have a memory controller that can do it. The memory controller in your i9 is rated to 2666 at stock voltage and no more, anything past that is overclocking--and with overclocking there are no guarantees. I would suggest manually raising the Vcore SOC ("uncore") and CPU VDD18 (i/o to memory) voltages as you likely only need a small bump to reach stability at 4133 if it can already do 4000 at XMP voltages.

Even the DRAM voltage may need a bit of an increase too because that memory is rated to run in pairs, and you are trying to run four sticks. It's normal to require more voltage when fully loading up the memory controller alone, and you are overclocking it too.
 
Reactions: TJ Hooker
Mar 22, 2019
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Okay thanks for the reply. Apologies - I know nothing at all about overclocking. Been building PCs for like 25 years but never needed to overclock anything! In fairness, now it's stable at 4000 I may just leave it there. Not like I'll notice the massive jump of 133mhz anyway.

Thanks for all the replies guys!
 

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