Question Performance of 7950X with 4-DIMM 128GB ram?

[BenHe]

Planning on building a workstation with 128GB DDR5, can't decide whether to go Intel, or AMD, or wait for Zen4 v-cache. Please advice:

Q1: I am a bit confused with 7950x's memory limitation. According to the spec, in the 2x2R configuration, max memory speed reduces from 5200MT/s to 3600MT/s. Does this mean that when 4 DIMMs are used, the total bandwidth is 4(DIMM)x3600MT/s, or does this actually mean 2(Channel)x3600MT/s?
Q2: Is there a possibility that this memory limitation can be alleviated with future firmware updates?
Q3: Will there be 64GB DDR5 sticks?

Any help would be much appreciated,
Cheers

Edit: Haven't bought anything yet, fully open to any alternative setup suggestions.

 

[BenHe]

In practice, bandwidth and latency both contribute to performance. Higher latency would waste CPU cycles and lower bandwidth would mean less data gets to all the cores which would then be data starved. DDR5-3600 does offer slightly higher bandwidth but the latency is so high that the higher bandwidth advantage is negated.

View attachment 69728

Even if we suppose that DDR5-3600 is running at CL28 (it will likely be higher), your CPU still has to wait 5.5ns more, during which your performance will suffer.

Try the latency calculator here: https://notkyon.moe/ram-latency2.htm

To match the latency of pedestrian DDR4, you need to buy expensive DDR5-6000 CL30 and hope it runs at that speed with 128GB.

View attachment 69731

I see your points now, thank you for the illustration of latencies!

 

[Doug S]

To be honest, all the prelaunch hype for DDR5 was just that. Hype. I was really excited that we would have DDR5-10000 by the end of 2022 and 64GB DIMMs would become a reality. Nope. Maybe after two more years?

Why did you think that? The DDR5 specification was announced to support DIMMs up to 128 GB, and they make these standards planning for future growth. Going to 64GB DIMMs so early in DDR5's life cycle wouldn't leave much room for future growth given we have some years to go before DDR6 appears.

DDR5-10000 is likely to be the pinnacle of overclocked DDR5 we see, given that the standard (at least so far, unless they update it down the road) only allows for speeds as high as DDR5-6400. The addition of ECC may complicate the ability to overclock, though that's probably more a latency hit than a throughput hit.

 

[igor_kavinski]

Why did you think that? The DDR5 specification was announced to support DIMMs up to 128 GB

DDR5 is Coming: First 64GB DDR5-4800 Modules from SK Hynix

www.anandtech.com

That gave me hope that we would get 64GB DIMMs soon. But I guess they don't care about us lowly consumers.

DDR5-8400: https://www.anandtech.com/show/15699/sk-hynix-ddr5-8400

They shouldn't spout such crap unless they are months away from introducing said product.

 

[Doug S]

DDR5 is Coming: First 64GB DDR5-4800 Modules from SK Hynix

www.anandtech.com

That gave me hope that we would get 64GB DIMMs soon. But I guess they don't care about us lowly consumers.
R5-8400: https://www.anandtech.com/show/15699/sk-hynix-ddr5-8400

They shouldn't spout such crap unless they are months away from introducing said product.

Registered DIMMs are their own animal, and can have more chips on the DIMM than UDIMMs. When those are released you and see the price, you probably won't want 64 GB DIMMs any longer!

 

[DrMrLordX]

Wait, are you guys telling me you cannot manually tune DDR5 on the AM5 platform? I know AMD may recommend a supported maximum frequency for different memory configurations, but cannot simply one adjust settings to get higher speeds?

Hand-tuning 128GB of DDR5 on AM5 will probably be very difficult, akin to hand-tuning 64GB of DDR4 on AM4. The memory controller and existing microcode may not support very many speeds with such a configuration (4x32GB).

 

[Harry_Wild]

DDR5 runs at PCIe 5 specs! 2 X the throughput of DDR4 RAM not taking the RAM speed difference!

 

[Tech Junky]

DDR5 runs at PCIe 5 specs! 2 X the throughput of DDR4 RAM not taking the RAM speed difference!

It also splits the overall performance due to how the controllers operate.

 

[sob727]

Has the situation evolved in any way over the past few months? I'm trying to create a 7950X workstation build with 128GB if it can be supported at decent speeds. This webpage seems to indicate Kingston at 5200 would work, I'm not sure how accurate it is ASUS QVL

 

[igor_kavinski]

This webpage seems to indicate Kingston at 5200 would work, I'm not sure how accurate it is ASUS QVL

Where did you get that impression on that page? They don't mention 4x32GB there.

EDIT: I see now. Had to search 5200 for the Kingston 4x32GB entries to appear. Interesting that 4x32GB was tested only on Kingston XMP kits. Maybe EXPO timings are too aggressive to support 128GB.

 

[sob727]

 

[sob727]

I'm no expert, I could be missing something.

 

[igor_kavinski]

I'm no expert, I could be missing something.

Don't think so. It's good to see AM5 memory support making progress. At launch and for several months after, most people couldn't get all DIMM slots populated to go above DDR5-3600. Even now, I think there is some issue with EXPO kits otherwise they would have at least one EXPO kit doing 128GB with DDR5-5200.

 

[sob727]

Is it your understanding that the incremental support is coming from new RAM sticks coming to market or Motherboard BIOS updates?

 

[igor_kavinski]

Is it your understanding that the incremental support is coming from new RAM chips or Motherboard BIOS updates?

I think BIOS updates. These are XMP kits so the BIOS has been tweaked to handle them. But they don't mention if the kits will work out of the box at these timings and speed or if manual tweaking is required. That is something you should email their tech support about to get an official answer.

 

[sob727]

Thanks - I might just buy Intel instead, seems too much of a hassle and too high of a risk to currently buy that AMD CPU if it's that difficult to pair it with memory sticks.

 

[igor_kavinski]

I think good decision.

ProArt Z790-CREATOR WIFI｜Motherboards｜ASUS Global

Built for creators, the ProArt Z790-Creator WiFi features 16+1 power stages (70A), PCIe® 5.0, DDR5 support, Thunderbolt⢠4, 10 Gb & 2.5 Gb LAN, WiFi 6E and four PCIe 4.0 M.2

www.asus.com

Their ProArt Z790 supports 192GB but only with 13th gen CPUs and timings are better.

But you should slso factor in which workloads you will be running. If those workloads may perform better on Ryzen due to it having 16 P-cores, Intel 13th gen may cost you more in the long run with higher power consumption and more heat output.

 

[CakeMonster]

96GB (2x48GB) kits have come out in the mean time at least.

 

[sob727]

@igor_kavinski That is exactly why I was leaning towards the 7950X in the beginning, virtually tied with Intel's 13900 for most workstation workloads (say within 5-10% max) BUT a consistently and significantly better performance per Watt in favor of AMD. And cooling the 13900 was more of a hassle. On the bright side I'm not in an immediate rush to buy.

 

[igor_kavinski]

On the bright side I'm not in an immediate rush to buy.

I think Zen 5 next year should have better memory support for 192GB DIMMs. So you may have to wait until May or June to get a 2nd gen AM5 workstation, with hopefully most of the early adopter kinks worked out from their experience with Zen 4.

 

[igor_kavinski]

96GB (2x48GB) kits have come out in the mean time at least.

F5-5600J4040D48GX2-TZ5NR - Specification - G.SKILL International Enterprise Co., Ltd.

Trident Z5 Neo RGB DDR5-5600 CL40-40-40-89 1.25V 96GB (2x48GB) AMD EXPO

www.gskill.com

That's a good kit. Able to do 5600 MT/s with just 1.1V.

No idea how it fares when two kits are used to populate all 4 DIMM slots.

 

[sob727]

I think Zen 5 next year should have better memory support for 192GB DIMMs. So you may have to wait until May or June to get a 2nd gen AM5 workstation, with hopefully most of the early adopter kinks worked out from their experience with Zen 4.

Almost 1 year out might be a bit too much for my taste. I was also waiting to see how TR5 comes out, more out of curiosity than anything else since I can't justify the costs of a Threadripper (even non-PRO). I will probably settle for a 7950X in a couple months when memory compatibility is a bit more established.

 

[sob727]

And for those who don't like RGB https://www.gskill.com/specification/165/396/1683011081/F5-5600J4040D48GX2-FX5-Specification

Neither are included in Asus' QVL yet though.

 

[JoeRambo]

Situation is improving with AMD memory compat. For example B650 Aorus Elite AX can't even boot with 2x32 sticks in it with whatever BIOS it came with. After Q-Flash update ( as easy as putting bios on usb, renaming to gigabyte.bin putting it in dedicated usb and pressing qflash button on the back) it works just great.
Compat, boot times, recovery from mild tuning failures are all improved.

I'd expect 1007B AGESA to work even better.