XMP question

[jelome1989]

Hey guys, are the advertised XMP speeds 100% stable? Will they 100% work with any board that support such speeds? I'm planning to buy high performance DDR4 (3600-4000mhz) RAM, because I hear it gives a decent performance boost in the games that I'll play (Starcraft 2, Cities Skyline, etc). I'll be paying a hefty premium for those so I want to be sure it works.

Thanks.

 

[BonzaiDuck]

It depends on your other hardware. Sometimes, an early motherboard release requires a BIOS update to handle higher memory speeds. Ultimately, though, you had best be careful per your second questions.

Go to the manufacturer's website for the memory brand or model you want, look for a "configurator" link, and see if your motherboard is in their list. Alternatively but no less useful: check the motherboard's QVL list to see if the manufacturer's model line is represented, even at a different speed spec.

The only other variable is the quality of RAM for meeting the touted spec. I use G.SKILL almost always. They never miss their mark. If they say a 3200 or 3400 kit will run at that speed, it will. Of course, if you're pushing the higher reaches of performance RAM, it will cost more and there may be more "shortcomings" among the available kits across manufacturers. And that's only logical inference. I can only vouch for my G.SKILL TridentZ kit.

 

[jelome1989]

So the compatibility of the board and the RAM is the deciding factor and not the board and RAM themselves as long as I'm not OCing past the advertised XMP of the RAM? Nice, that's good to hear because my plan is to buy the G.SKILL TridentZ kit (either the 3600mhz cl15 or the 4000mhz cl19 one).

 

[Billb2]

XMP is just some computer engineer's guess at what will work on the widest possible range of motherboards. It's a crap shoot whether it will actually work .

 

[VirtualLarry]

XMP is just some computer engineer's guess at what will work on the widest possible range of motherboards. It's a crap shoot whether it will actually work .

Yeah, pretty much. XMP is RAM overclocking, and overclocking is always YMMV. I figure, they probably do test the RAM (individually? or lot test? Those RAM chip at-speed testers are millions of dollars), on SOME rig at those speeds, before they sell them, but every rig has slightly different tolerances. Even different CPUs will have slight different CPU integrated memory controller tolerances. Some might need bumping up of voltages (don't ask me which ones) to make the faster RAM stable at XMP settings.

 

[jelome1989]

... but every rig has slightly different tolerances. Even different CPUs will have slight different CPU integrated memory controller tolerances. Some might need bumping up of voltages (don't ask me which ones) to make the faster RAM stable at XMP settings.

So CPUs are part of the equation as well? Will getting higher end boards increase my chances? Or it's simply what Billb2 said, pretty much hit or miss?

 

[John Connor]

Don't you have to use a XMP profile for high speed RAM? They all say like 3000 MHz and then the fine print says, with an XMP profile. I always thought you had to profile your RAM to get the advertised speed. Or am I wrong? Will the advertised speed work without OCing?

 

[Billb2]

Don't you have to use a XMP profile for high speed RAM? They all say like 3000 MHz and then the fine print says, with an XMP profile. I always thought you had to profile your RAM to get the advertised speed. Or am I wrong? Will the advertised speed work without OCing?

The simple (simplistic) answer:
All memory has "SPD tables" programmed into the memory. These tables are used to match the memory's timings to the speed at which it is running. When a computer starts up the memory runs at the speed set in the BIOS and the appropriate timings for that speed are set from the memory's SPD tables.
XMP Profiles are just memory timing tables that also include a setting for the memory voltage (ie. increased voltage). Since many computer motherboards don't have XMP capability (ie can't set memory voltages automatically) XMP profiles are not set "automatically" at staerup and you have to choose to use them (by selecting XMP in the BIOS).

Of course, if the motherboard supports it, you can manually set the memory speed, timings and voltage to whatever you want and not use XMP to guess at what will work.

 

[John Connor]

Thanks for the explanation.

 

[BonzaiDuck]

He saved me the trouble.

You could conceivably disable XMP and set the RAM manually to its spec speed, voltage and timings. Using a manual setting may be part of the "YMMV" uncertainty. There is a pile of secondary timings defaulted to "Auto" which the XMP profile may set more aggressively. So if you try to configure the RAM manually, those timings might not be optimal.