2400 RAM Showing as 2133 on Kaby Lake Board

raotor

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Nov 3, 2007
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Hello,

Just put together a new Kaby Lake machine using an Asus PRIME B250 motherboard and a single stick of Corsair Vengeance 2400 DDR4 RAM. The memory is certified in Asus's QVL so there should be no issue with compatibility so I was puzzled why when entering the BIOS that the RAM speed was reported as 2133 Mhz. Now, my understanding of Kaby Lake boards is that they natively support 2400 Mhz RAM.

I saw that there was an XMP profile available supporting 2400 speed and selected that. This reports a 2400 Mhz memory frequency when looking at the advanced page details but when viewing the EZ mode info the memory speed is still reported as 2133. I had assumed that I would not need to fiddle with XMP settings to get a 2400 Mhz stick of RAM on a new Kaby Lake board to run at the default speed.

I would appreciate it if someone could enlighten me as to what's going on please.

Thanks.
 

raotor

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Thanks but as mentioned, a speed of 2400 is showing under the Advanced UEFI options report. What I am confused over is why this 2400 rated stick of RAM isn't being recognized "out of the box" and without resorting to using XMP profiles as its proper speed.
 

marko55

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Nov 29, 2015
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Oh. That's just default behavior. The default base memory clock speed for DDR4 and your CPU is 2133. Some motherboards will attempt to auto-clock RAM to their XMP settings but its not always the case. You also don't really want the BIOS to try to auto-clock your RAM all the time since sometimes your RAM is something like 3200 and if that XMP profile were to auto-enable upon first boot and there's a problem with that, you're never gonna get in to the BIOS.

You want your board to simply clock the RAM to its base speed of 2133 so the machine can POST and THEN you can try to enable XMP and clock your RAM to its full potential. If it works, great. If it doesn't work then you know you can clear your CMOS and start from scratch because your memory will auto-clock to its base 2133 after the reset and you can POST in to your BIOS.
 

raotor

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Thanks for the info. I'm puzzled as I was of the belief that Kaby Lake chipset boards such as the one I have support DDR4 2400 natively as long as you're using a 2400 rated memory stick. I know the previous generation Sky Lake boards only supported 2133 MHz RAM regardless of how fast the memory actually was so thought I'd have to do nothing to have the RAM recognized as it's native speed of 2400.