ASUS PRIME X399-A 512GB RAM Possible?

the website for my motherboard claims the maximum supported amount of RAM is 128GB.

however, dmidecode claims the maximum is 512GB.

# dmidecode 3.2
Getting SMBIOS data from sysfs.
SMBIOS 3.0.0 present.

Handle 0x0037, DMI type 16, 23 bytes
Physical Memory Array
        Location: System Board Or Motherboard
        Use: System Memory
        Error Correction Type: None
        Maximum Capacity: 512 GB
        Error Information Handle: 0x0036
        Number Of Devices: 8

does this mean that 8x64GB on my motherboard is possible? or is this a bug with dmidecode?
breaking past the 128GB barrier would be very useful to me.

1 Like

Short Answer:
No, for DDR4 RAM value on the producer site or manual is the value that is your limit.

Long Answer:
Physical Memory Array (PMA) in case of SMBIOS is theoretical max capacity of all the devices that serve as memory (that is RAM, VIDEO (in old video cards), FLASH, …) for CPU. So it always should to be larger than the MAX supported RAM (as DDR4 RAM modules) - to avoid issues like video card “eating” the capacity of RAM.
Usually memory/RAM max capacities are growing with power of 2 (128, 256, 512).
In order for the system to support 128GB you need to have at least PMA of max capacity 256GB. And I guess that manufactures do want to play safe.

Separate matter is support for maximum memory capacity of DDR4 module. Which also in your case is max 16GB.

EDIT: Actually I wonder if this PMA is is just not completely obsolete and kept strictly for compatibility in case you would like to run super old operating system.


Do unbuffered unregistered 64gb dimms even exist?

Not at this point in time.

I’d wecome it if maybe @wendell would poke around in Zen+/Zen 2’s firmware to unlock RDIMM support like in that Chinese Zen 1-based CPU.

When looking at the prices and availability, I’d welcome using 32 or 64 GB DDR4-3200 (L)RIMMs on Ryzen/Threadripper systems…

One can only dream.

In my opnion AMD should have allowed RDIMM support on Threadripper systems, 4- instead of 8-channel and 1 TB instead of 2 TB in total memory support would have been enough to differentiate them from the Epyc line-up.

Must be a trade-off to make, in silicon or on the board? AMD chose to support “gaming” speeds at 3ghz+ rather than much slower but more common registered DIMMs?

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