For all those who have struggled with purchasing DDR4 to upgrade your ram, then found it only runs at 2400MHz instead of the advertised 2666MHz, here is some background on common misconceptions and then the real truth and resolution. The first section just explains most ofour common misconceptions about single vs. dual rank and sidedness. They however are NOT the culprit, but still good for a working understanding of how DDR4 works.
Section 1. After spending a bit of time learning about single sided vs. double sided, and single rank vs. double rank, there was much confusion about these two different definitions and functions. They are however NOT the turd in the punchbowl of incompatibility, and lower clock speeds. My bad for the assumption, it's what I had learned from other MR posts. For clarity and because so many of us don't fully understand how DDR4 works very well, I'm attaching a pdf that explains these functions and why they aren't the culprit.
Section 2. What I did learn however is there is on a great deal of DDR4 today that has an "XMP 2,0" profile by Intel. It modifies the bios to overclock for example 2400MT/s DDR4 to 2666MT/s, and thus manufacturers are advertising DDR4 at the higher "overlocked" speeds as normal DDR4. Since Apple does not support XMP 2.0, we get the DDR4's normal clock speeds, not the advertised speed. Very misleading.
Here is a quote from another Mr member concerning this. This is what is causing the majority of these 2019 iMac DDR4 mismatches. There should be some sort of truth in advertising law associated with this, but we all know what the chances of that are.
https://forums.macrumors.com/threads/2019-imac-ram-2400mhz.2176657/#post-27258169
Here is an Amazon DDR4 ad from Micron (Crucial's parent company), misleading someone on here with this kind of ad. Look down below the picture on the right for more info, you'll see they post this in a pretty inconspicuous spot, very easy to miss.
https://www.amazon.com/gp/product/B06XRBS4Y5
My advise? I ONLY buy ram that has been listed as "specifically for," my Mac. Either official Crucial, or some other OEM who manufactures their own ram and lists it as specifically for my model only.
Section 1. After spending a bit of time learning about single sided vs. double sided, and single rank vs. double rank, there was much confusion about these two different definitions and functions. They are however NOT the turd in the punchbowl of incompatibility, and lower clock speeds. My bad for the assumption, it's what I had learned from other MR posts. For clarity and because so many of us don't fully understand how DDR4 works very well, I'm attaching a pdf that explains these functions and why they aren't the culprit.
Section 2. What I did learn however is there is on a great deal of DDR4 today that has an "XMP 2,0" profile by Intel. It modifies the bios to overclock for example 2400MT/s DDR4 to 2666MT/s, and thus manufacturers are advertising DDR4 at the higher "overlocked" speeds as normal DDR4. Since Apple does not support XMP 2.0, we get the DDR4's normal clock speeds, not the advertised speed. Very misleading.
Here is a quote from another Mr member concerning this. This is what is causing the majority of these 2019 iMac DDR4 mismatches. There should be some sort of truth in advertising law associated with this, but we all know what the chances of that are.
https://forums.macrumors.com/threads/2019-imac-ram-2400mhz.2176657/#post-27258169
Here is an Amazon DDR4 ad from Micron (Crucial's parent company), misleading someone on here with this kind of ad. Look down below the picture on the right for more info, you'll see they post this in a pretty inconspicuous spot, very easy to miss.
https://www.amazon.com/gp/product/B06XRBS4Y5
My advise? I ONLY buy ram that has been listed as "specifically for," my Mac. Either official Crucial, or some other OEM who manufactures their own ram and lists it as specifically for my model only.
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