Question on DDR5 memory speed vs CPU capability

Have installed a Gigabyte X670 Aorus Elite AX mobo, AMD Ryzen 7 7800X3D CPU and two sticks G.Skill DDR5 6000 memory (2 x 16Gb) in slots A2 and B2 on the mobo. I have EXPO1 enabled in the BIOS (the current FA5e version).

I added two identical G.Skill DDR5 6000 (2x16Gb) sticks to mobo slots A1 and B1 to boost the capacity to 64Gb. The mobo wouldn't POST. After several power off/on I finally got a "BIOS failed to load" message and to "load the default BIOS". I did that and it finally booted to Windows. I checked the memory speed (wmic memorychip get speed) and the four sticks were at 3500 each.

I went back to the BIOS and found that EXPO1 was Disabled but DDR5 Auto Booster was Enabled. I shut down and removed the two new sticks, rebooted and enabled EXPO1. After some training I got to Windows. I checked the memory speed and it was 6000.

So my questions is: apparently the AMD Ryzen 7 7800 X3D can't support four sticks of DDR5 6000 memory. Is this a correct assumption? Seems stupid to manufacture a chip that can't use all 4 memory slots at the DDR5 6000 speed.

Thanks.

Looking at this support page for your Gigabyte motherboard 4 sticks of G.Skill DDR5 ram doesn't appear to be supported.


This is for rev 1.3 of this motherboard. There is a link at the top of page for 1.0 - 1.2 versions of your board.

Using rev 1.3. So it looks like only up to DDR5 4800 is supported on all 4 slots. It was so much simpler using DDR4 memory. Never had an issue with 64G DDR4 3200 on my old build.

Thanks for your reply!

rzn6jw said:

Using rev 1.3. So it looks like only up to DDR5 4800 is supported on all 4 slots. It was so much simpler using DDR4 memory. Never had an issue with 64G DDR4 3200 on my old build.

Thanks for your reply!

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It is also an issue with Intel Z790 motherboards which also use DDR5 ram. Seems like AMD, Intel and the board manufacturers cannot get it to work properly.

That sort of thing isn't new. I used some DDR4 3800 RAM on an Asus X570 (AMD) motherboard. Worked fine with 2 DIIMs, but after I upgraded to 4 identical DIMMS, I had to downclock to 3600. (The DIMMS were on the supported list for 2, but not 4.)

It is generally not a good idea to combine memory from two different sets purchased separately. They are not necessarily identical, they may use different chips even if the model number is the same. In addition, even if they use the same chips they may have enough variation in manufacturing to cause timing issues. This will be exacerbated by using 4 sticks of ram instead of two. 4 sticks are generally harder to get stable than 2, and need to run at a lower speed.

I only buy a set of two dimm at the capacity and speed i want. You can get 2x24, 2x32, and 2x48 now at speeds at or exceeding 6400 MT/s. You also need to make sure it is compatible with your motherboard. Don’t just go by the motherboard memory compatibility list. Those are not updated. Check the memory vendor’s motherboard compatibility list.

As I suspected, your CPU cannot handle the full 6000 speed. It can do up to 5200, see here: https://www.amd.com/en/products/processors/desktops/ryzen/7000-series/amd-ryzen-7-7800x3d.html

rzn6jw said:

Seems stupid to manufacture a chip that can't use all 4 memory slots at the DDR5 6000 speed.

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That is the reason I plan to buy 2x32GB instead of 4x16GB. The cost is the same.

Before you buy make sure your CPU and your motherboard are compatible with them.

spapakons said:

As I suspected, your CPU cannot handle the full 6000 speed. It can do up to 5200, see here: https://www.amd.com/en/products/processors/desktops/ryzen/7000-series/amd-ryzen-7-7800x3d.html

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It ran with two DDR5 6000 DIMMs, but not 4. Note that it lists DDR5 3600 with 4 DIMMs.

6000, even with 2 DIMMs, is regarded as overclocking. Gigabyte lists no DDR5 6000 as compatible with 4 DIMMs, at any capacity.

Gigabyte lists a single 4 DIMM DDR5 5200 set as compatible. It's 4 X 48GB (192GB total). Amazon has it for a mere $630US.

Before buying anything new, I would try to manually underclock the RAM to 5200. You may not have the maximum performance of 6000 speed, but it is better than giving a fortune for new modules.

Marcus Vinicus said:

It is also an issue with Intel Z790 motherboards which also use DDR5 ram. Seems like AMD, Intel and the board manufacturers cannot get it to work properly.

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my Asus Z790 with DDR5, 4 sticks (64GB) has no issues at xmp in bios at 6600. not sure what to tell you why you can't.

retiredat44 said:

my Asus Z790 with DDR5, 4 sticks (64GB) has no issues at xmp in bios at 6600. not sure what to tell you why you can't.

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Your RAM isn't on the QVL (qualified vendors list) for 4 DIMMs for the Z90-H. It is, however, OK for 2 DIMMs.


Not being on the QVL for 4 DIMMs doesn't absolutely mean that it won't work.

But you're lucky, I guess.

retiredat44 said:

my Asus Z790 with DDR5, 4 sticks (64GB) has no issues at xmp in bios at 6600. not sure what to tell you why you can't.

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I was referring to it being difficult to get a PC with 4 sticks of DDr5 ram running at higher than 4800mhz. There are numerous threads over at the Asus Forums about this.

Also, I only have 2 sticks of DDR5 on my PC and there is no point me trying to get 4 sticks working as I don't have any use for more than the 64GB currently installed.

If you've got DDR5 ram running 4 sticks at 6600mhz you're one of the very few I've ever heard of who've got a stable system.

rzn6jw said:

So my questions is: apparently the AMD Ryzen 7 7800 X3D can't support four sticks of DDR5 6000 memory. Is this a correct assumption? Seems stupid to manufacture a chip that can't use all 4 memory slots at the DDR5 6000 speed.

Thanks.

Click to expand...

It's the mobo with the limit, not the CPU.

As said in an earlier post, the RAM speed depends on the CPU speed. If the CPU speed is a multiple of, 200 say, maximum RAM speed must also be a multiple of 200. Same if CPU speed is a multiple of 166, say, the maximum RAM speed must also be a multiple of 166. You cannot force a higher RAM speed which is not a multiple of the least common factor, that's why the RAM cannot run at 6000MHz and works at 5200MHz, if I remember correctly. Replacing the CPU with one having speed multiple of the appropriate least common factor you can then use that RAM at 6000.

pparks1 said:

It's the mobo with the limit, not the CPU.

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AMD specifies a maximum frequency for the RAM.


It's not a hard limit. I presume that most motherboards permit higher frequency RAM, but it's regarded as overclocking.

Either the CPU or the motherboard, the point is that you have to match the RAM to your system. If the system doesn't support 6000MHz you usually cannot just force it. You must change RAM modules with ones that match the system or compromise with less than maximum operating speed. It brings back memories of DDR2 800MHz RAM modules that only worked at 667MHz if the CPU FSB was 166MHz. If you wanted the full 800MHz speed the CPU FSB should be 200MHz. None was the wiser, all of us that wanted maximum speed weren't stupid paying more for a CPU with 200MHz FSB.

spapakons said:

Either the CPU or the motherboard, the point is that you have to match the RAM to your system. If the system doesn't support 6000MHz you usually cannot just force it. You must change RAM modules with ones that match the system or compromise with less than maximum operating speed. It brings back memories of DDR2 800MHz RAM modules that only worked at 667MHz if the CPU FSB was 166MHz. If you wanted the full 800MHz speed the CPU FSB should be 200MHz. None was the wiser, all of us that wanted maximum speed weren't stupid paying more for a CPU with 200MHz FSB.

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How do you know what "Matches the Motherboard"? There is in the spec a set of supported speeds. If you run at jdec(SPD) speed you will always be successful. But any maximum speed over jdec is considered overclocking. Motheboard vendors usually paranthetically indicate this with OC in their specs. These are XMP profiles and whatever it is called on AMD EXPO. These aren't guaranteed p and that is why each board manufacturer has a QVL list for each model. These are not at all comprehensive or kept up-to-date.

The maximum memory frequency you can achieve depends on mostly the motherboard - quality of power delivery and trace layout - but also on the processor itself. The processor has an Integrated Memory Controller that controls the transfer of data and commands between the CPU and memory. The quality of the IMC from processor to processor varies a good bit. It also depends on the quality of power delivery by the motherboard. There is also the quality of the RAM chips and the number of sticks. You probably are using the same RAM chips between day 6000 and 7200 MT/s sticks, but the chips on the higher frequency are binned for higher quality.

Due to the above, this is why I say the XMP and EXPO are not guaranteed. Manufacturers do their best to spec their product to just work, but there are many external variables. The higher you go in frequency, the less likely you are to succeed without some to a lot of knowledge and work.

You can go above the advertised speeds but you either have to be a lucky or spend some time tuning memory voltages and timing.

Sorry, didn't mean to ramble on, but I painfully typed it on my phone so gonna post anyhow.

spapakons said:

As I suspected, your CPU cannot handle the full 6000 speed. It can do up to 5200, see here: https://www.amd.com/en/products/processors/desktops/ryzen/7000-series/amd-ryzen-7-7800x3d.html

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They always only list the highest jdec frequency in processor specs, not XMP or EXPO. 6000 is supported by the board for only 2, not 4 sticks. This is the problem as mentioned by @bobkn and @Marcus Vinicus. Only 4800 MT/s are listed in the QVL for 4 sticks. And maybe the fact that there are two separate sets of 2 sticks that were manufactured at 2 different times with maybe different innards.