I just assembled my new PC with X399 Taichi MB and 4 x 8GB memories but the MB only reports 24GB of total memory. (Both in BIOS and in windows)

I've tried several configuration and it seems that whatever put in memory slot A1 or A2 doesn't get counted. However, the MB seems to still recognize it. e.g if I put A2, B2, C2, D2, the memory is running in Quadruple mode with total 24GB, but if I put only B2, C2, D2, it runs in Single channel mode with 24GB.

I also tried putting the memories in B1, B2, C2, D2. Then it reported 32GB total but only runs in Single channel mode, which is too slow.

I also tried using a single slot to narrow down the issues. System doesn't boot if I use A1 or A2 alone, but using B1 or B2 works.

It would be highly appreciated if you could provided some support on this.

The memory is G.Skill F2666C16-8GRB. BIOS version is 3.30.

Thank you!

Under the OC Tweaker page in BIOS there's a section:

DRAM Timing Configuration

DRAM Information

XMP 2.0 Profile 1: DDR4-2666 16-16-16-36 1.20V

There's a setting "Load XMP Setting" right under it, which is set to Auto. If I want to change it, there's only "Auto" and "XMP 2.0 Profile 1" available.

DDR4_A1 : None

DDR4_A2 : None

Hope this provides enough information

Very odd.

1. Even Google hasn't heard of this F2666 model of yours. Now, I'm not a googling guru but still, 0 hits on that model? Are you sure you haven't been scammed?

2. Check the manual for populating the proper RAM slots. http://asrock.pc.cdn.bitgravity.com/Manual/X399%20Taichi.pdf

Check and even better, re-seat the RAM modules in their respective places. DDR4 slots are known for misleading novice users. RAM must be seated 100% correctly in the proper slots.

3. Check if CPU is seated properly and it doesn't have bent pins. Some Foxconn TR4 socket mechanisms are known to be very difficult to install properly. It's also another common mistake, even for advanced builders. Even better - re-seat the CPU once again. I've seen guys having similar issues to yours, where bent pins or CPU misalignment was the culprit.

3. Check for cabling issues - bad plugs, forgotten secondary PSU cables, etc.

4. Do a proper CMOS reset. I know 'proper' sounds stupid but many times it's not just as simple as a push of a button. Dig around here. There are good guides. Or just ask, I'll write as soon as I can.

5. Try running each RAM module solo. It should be in slot A2 but try others if it won't work there. Clear CMOS every time! From BIOS select 'Load XMP Setting' and choose 'XMP 2.0 Profile 1'. Save and exit. Boot Win, Lin or memtest and test extensively. Rinse and repeat for each RAM module.

6. Although at this point it should be clear (at least to you) if your memory or something else is wrong, it's worth checking https://www.jzelectronic.de/jz2/index.php and flash the latest beta. Always reboot once, then power off and clear CMOS, before and after flashing new BIOS.

7. Last but not least, check the QVL https://www.asrock.com/mb/AMD/X399%20Taichi/index.asp#Memory

It states that many G.Skill modules can run @ 3200 (and above) in Quad Channel. Maybe it's time for a swap?

Keep us posted! Fingers crossed!

Thanks a lot for the detailed reply!

1. The model I'm using was purchased here:

https://www.alternate.de/G-Skill/DIMM-32-GB-DDR4-2666-Arbeitsspeicher/html/product/1173456

It's a set of 4 x 8GB. This is a very popular site in Germany for buying computer parts so not very likely to be scammed. (hopefully :)

2. I followed the MB manual and seated them in A2, B2, C2, D2. Got 24GB only :( It runs in Quad Channel mode though, so somehow it's recognized as properly seated.

3. This might be the reason but I'm running out of thermal paste at the moment. Will try to re-seat the CPU later.

4. Have no idea how this could be done. Only tried the CMOS reset button or removing the battery but that didn't help.

5. Solo RAM in B1 is working with any of the 4 RAM but none is working solo in A2. :(

6. Just flashed from 3.20 to 3.30 today, hoping that would solve the issue. But no luck.

7. Yes. I checked there, could not find my model though :(

You cant find it because he forgot the frist 2 letters

https://www.gskill.com/en/product/f4-2666c16q-32grb" rel="nofollow - https://www.gskill.com/en/product/f4-2666c16q-32grb

Try running it at higher 3000 or lower 2400 MHZ

ASRock memory support does not state any 2666 RAM Support from GSkill

If nothing works send it back and order a new one from the Supportet list

Silly me! I had this unsettling feeling something with the numbering wasn't right. :D

@mhp - try running the memory banks in pairs in A2 & B2 slots. Try all possible combinations (2^4=16 in total) with a good CMOS reset in between. Don't touch anything in BIOS, just do a reset before, then memtest each combo. I guess it will take some time. :D

Alternate aren't bad but I've always preferred mindfactory myself. They have very competitive prices and excellent service. Another place for ASRock in Germoney is JZ https://www.jzelectronic.de/jz2/index.php" rel="nofollow - https://www.jzelectronic.de/jz2/index.php

If all fails, I'm with Animalm4st3r this time. Return the RAM and pick something from the QVL. Threadripper 2 (Zen 2) has way better memory compatibility, and you didn't state your CPU model. Although, other people here mention bad DIMM slot on the mobo, too. So, you never know.

happy threadripping!

Just chiming in to say I had the same problem, and the same solution.  I have an x399 Professional Gaming motherboard, Threadripper 2990wx, and 4 x 8GB Kingston HyperX 2400 DDR4 (HX424C15FW2K4/32).  Switching out RAM sticks didn't work.  Unplugging the PSU and mashing the Clear CMOS button for ten seconds, then upgrading to BIOS 2.2, then to 3.3, didn't solve the problem.  (My computer would just power cycle continually with 2.2 as it couldn't recognize the Threadripper 2--I had to use the Flashback button and a USB stick without powering on [cool feature!].)  Then I took off the cooler and TIM, raised and lowered the TR4 bracket down as straight as I could, reapplied TIM and cooler, and ? moë! Problem solved!  Thanks!