Tell us about the motherboard -
Also, here are the two processors compared.
I replaced 3 motherboards for my child the first was asrock X299M Extreme4 second asrock X299 Extreme4 and the last one Gigabyte X299 UD4 Pro. I was thinking the problem is with asrock motherboards because these memory sticks was working fine in my main pc ROG RAMPAGE VI EXTREME OMEGA so i go for gigabyte and again the same problem. The last thing i done just instal my main cpu 9800x to that gigabyte mobo and all 4 rams start working fine. In 7640x cpu memory specifications says Max # of Memory Channels 2 Is it means just 2 sticks can be used?
What model board and manufacturer - GIGABYTE X299 UD4 Pro
does it have the latest bios - not sure but asrock had
what memory it supports - Support DDR4 up to 4400(O.C.)
what is the speed of the memory -3200MHz HyperX HX432C16PB3K4/16
is the 7640x supported - Yes
Drop the speed of the memory to 2666. Make sure the board has the latest bios. I am not concerned with the asrock board.
Also, you may want to try different, lower speed, memory.
Most i5 motherboards support 4 sticks of DDR4, but in a dual-Channel configuration. This means that the CPU reads from 2 memory sticks at a time. In a quad channel setup, the CPU will read from 4 sticks of memory at a time. Each stick provides 64 bits of data to the CPU. So, you can see that a quad-channel CPU will require more pins than a dual channel. This is why CookieMania66 pointed out that this is not a feature of most desktop CPUs. What is your application ? Most games are GPU bound, not CPU bound, so most of us spend money on our GPUs.