Optimal compatible RAM

[Bellzemos]

Hi,

will "Corsair Vengeance LPX Black DDR4-2400, CL14 - 32 GB Kit" RAM work on an Asus Prime Z270-A motherboard with a Intel Core i7-7700K CPU?

This is the exact model of the RAM kit in question: tCMK32GX4M2A2400C14. Will it work and is it the most optimal RAM kit I can get for my setup?

Thank you!

 

[thx1138v2]

Although both the mobo and CPU support that speed, that particular model # is not in the Asus Qualified Vendor List (QVL) for that mobo.

Will it work? Probably.

Is it optimal? probably not.

Search "CMK32GX4M2A" in the following document for alternatives:
http://dlcdnet.asus.com/pub/ASUS/mb/LGA1151/TUF_Z270_MARK1/Z270_PRIME_TUF_STRIX_QVL.pdf?_ga=2.16418486.1087316081.1502274617-988497514.1502274617

 

[Bellzemos]

It has quite low CL (14) and it's the maximum speed (2400) that's supported by the CPU and MOBO (without OC-ing). And it's 2x 16GB, dual channel, as the CPU supports. Why isn't it optimal?

 

[Kasper Jorgensen]

Those supported lists only mean that they have tested that specific model. It doesn't mean other specific models will not work or work less good.

 

[thx1138v2]

Those supported lists only mean that they have tested that specific model. It doesn't mean other specific models will not work or work less good.

Exactly - it's untested so unknown.

 

[Kasper Jorgensen]

I wouldn't call it unknown. For example corsair vengeance lpx has many models, because they test their ram and sell them to work at a specific speed, the lpx are still the same chips. It's Like Intel does with cpu. As long as they are made under the ddr4 standard they should work, at least at 1,2v 2133 mhz as the standard specify.

 

[Karadjgne]

There's half a hundred different brands of ram. With each vendor there's half a dozen different speeds. Each serial number is specific to one type, but serial numbers can change with color, heatsink design, size, CL etc so when you add up all the separate serial numbers possible per speed, CL, size, color, heatsink, design, batch, vendor you'd end up with a QVL of several hundred pages long, entailing hundreds of thousands of man hours testing, quantifying, catagorixing, retesting, etc etc etc. No vendor will do that, ever, so what you end up with is a few lpx tested at various speeds and if they work as advertised, chances are almost perfect that any other lpx will also work. Seriously doubtful that lpx working at 2666 and lpx working at 2133 will mean that lpx won't work at 2400.

CMK- Corsair designation/type
32G- Size of kit batched
X4- Sticks in kit
M2A- color/design/type
2400- Speed
C14- timing
XXXX- batch number, usually sequential.

M2A might be lpx black color, M3A might be lpx red color, the vendors won't test both, so only one of any specific style might be tested as color doesn't mean anything. Neither does heatsink styling etc.

 

[Bellzemos]

Thank you all for your comments!

So, I'm getting this kit:
http://www.corsair.com/en-gb/vengeance-lpx-32gb-2x16gb-ddr4-dram-2400mhz-c14-memory-kit-black-cmk32gx4m2a2400c14

It's 2x 16GB modules, even though it says "X4" - I gues that means 2 pieces. Maybe means 2x 2 sides, dunno.

Anyway, on the upper link the specs for this kit are:
SPD Latency
15-15-15-36

SPD Speed
2133MHz

SPD Voltage
1.2V

Speed Rating
PC4-19200 (2400MHz)

Tested Latency
14-16-16-31

Tested Speed
2400MHz

So what does that really mean? i7-7700K (without OC) is supposed to support 2133 MHz and 2400 MHz RAM. So what will my RAM kit's speed be when insert it in the MOBO?

2133 with XMP disabled and 2400 with XMP enabled in BIOS? Or even higher, meaning it will be overclocked? What about latencies, will they automatically get lower if I turn on XMP?

The MOBO is Asus Prime Z270-A.

I've never dealt with XMP before, my last PC build was quite some time ago.

Thanx!

 

[Karadjgne]

Xmp is Intel eXtreme Memory Profile. Skylake cpus memory controller runs at 2133, kabylake runs 2400. In each set of ram, there's certain parameters, this'll include voltage, timings, speeds per data rate (ddr4 is double data rate version 4).
This info can be found on the jadec table that's available if you use cpu-z or other software that'll read the ram bios.

All that said, your ddr4 default speed is 2133. If you just plug it in, that's what it'll run at, which is fine, plug-n-play. You can lower speeds, if you choose to (dunno why) and you'll see the speeds and associated info on the jadec table. Xmp is basically the optimal speed as set by individual ram, so if you buy 2400, it'll start at 2133,but you can enable xmp which will use predetermined optimal parameters and bump it to 2400. If you buy 3200, it'll start at 2133, but xmp1 will be 3200, xmp2 might be 2933, xmp3 2666, xmp4 2400 or similar. Each will have optimal timings and voltages etc pre-set. Xmp just eliminates any user guess work to set higher speeds.

There's 2 trains of thought about the (OC) listing on the ram. Mobo side, a Z270 for instance, is designed primarily for a kabylake cpu. So 2133, 2400 will be listed as normal operating speeds. Anything over normal cpu supported could be considered OC, so 3200 would require manual intervention, be it enabling xmp or manual OC to something higher than 2400. The other train of thought is that if you buy 3200,it has a factory setting for that speed, so is as is, it'll only be OC if pushed beyond 3200. But many systems, for one reason or another, be it the voltage needed by the MC, voltage needed by the ram for stability at higher speeds, will require extra voltage or extra speed or extra current or extra anything set in the bios. This is a departure from stock, therefore its most definitely OC of some sort. So to get ram stability at anything higher than the base 2400 could require OC of the cpu. This way of thinking is supported by the fact that non-OC motherboards will only support 2133, 2400 ram.

Pretty much both ways mean the same thing, in order to reach high speeds, something is going to see OC, either cpu or ram or both.

 

[Bellzemos]

Thank you very much for the explanation! I didn't even know that 2133 was for skylake and the 2400 for kaby lake.

So, does that mean that if I get the CMK32GX4M2A2400C14 RAM (from the link in my last post) it will run at 2400 MHz with 14CL at deafault? And by default means no overclocking the CPU or RAM and having XMP disabled?

Am I getting it right? If yes, that the exact RAM kit I'll get!

Again, thank you!

 

[Kasper Jorgensen]

Kaby lake will run it at 2133mhz 1.2v as default. 2133mhz is the jdec standard for ddr4 ram. Just enable xmp1 profile and it will run at the higher speed.

 

[Bellzemos]

Oh OK, I tought that paired with a Skylake CPU it will run at 2133 and paired with a Kaby Lake it will run at 2400.

So for the RAM in question (CMK32GX4M2A2400C14), if I enable the XMP, this will make the RAM run at 2400 MHz? Or even higher MHz? I'd like to run it at 2400 as that's what it was tested for.

If I look at the CMK32GX4M2A2400C14's specs table I see that the JEDEC CL is 15 and tested CL is 14. So will enabling the XMP in BIOS make my RAM run at 2400 MHz with CL14 (instead at 2133 with CL15 with XMP disabled)?

Thank you so much for bothering.

 

[Karadjgne]

Run XMP enabled. It'll run the ram automatic at 2400 MHz CL14 with the correct voltage as specified by the ram.

 

[Bellzemos]

I will. I will get that exact RAM kit and enable XMP in BIOS. Thank you so much. This topic is solved.