Ah, OK, you actually have an even worse problem: because the size of RAM in Channel A (2x4GB) does not match the size of RAM in Channel B (2x8GB), the RAM is not running in dual channel mode.I thought about that.. but according to my system info... that's not the problem....
I see... I guess I do need to buy that extra RAM... thanks.. I'll let you know what happens when its popped in...Ah, OK, you actually have an even worse problem: because the size of RAM in Channel A (2x4GB) does not match the size of RAM in Channel B (2x8GB), the RAM is not running in dual channel mode.
It is instead running in flex mode: where the first 8GB is running in dual channel mode, and the remaining 16GB is running in single channel mode, which effectively halves the speed of the 16 GB.
You would be better to order the RAM as follows:
Slot 1 - 4GB
Slot 2 - 8GB
Slot 3 - 4GB
Slot 4 - 8GB
This will run in dual channel mode, but the RAM speed will drop to 2133 MHz.
Really, the optimum solution is to have 32 GB of matched size sticks (2x16GB or 4x8GB), which will run both in dual channel and at 2667 MHz.
Hope this is not too confusing
btw, if you plan to use 4x8GB sticks, and they aren't all identical (manufacturer and part number), you may need to put them in order AABB, instead of ABAB, to get them to run at 2667 MHz. This is just a quirk of the 2020 iMac, it is not a problem.I see... I guess I do need to buy that extra RAM... thanks.. I'll let you know what happens when its popped in...
Any clue what is the issue ?