Thoughts on Am5 motherboards for a workstation build

So I picked up a Ryzen 7900x for a really good price. Like stupid good price. So now I am looking to nail down my internals. This is going to be more work build than gaming. I have my eye on two different mother boards Both are ASUS one is the

ProArt Creator b650

The Rog Strix b650 E gaming wif

i. one is marketed as a more creator motherboard which I am an developer and visual artist so that makes some sense, and the other more Game oriented which I really do not care all that much about. but both have some features that I find compelling.

1.both boards offer support for ecc memory whenever ddr5 ECC memory comes available

  1. Multiple gpu support, for future endeavors in machine learning.

Now I am leaning towards the Rog Strix Model, even though its about 100 dollars more, I get more NVME drive support. which helps future expandability. On the Rog Strix Model the bifurcation is a bit weird. Asus says they are PCIE gen 5 X16 but if you have a dual gpu setup they are bifurcated X 8 X 4 I find that a bit odd. they are PCIE gen 5 bandwidth but all cards are PCIE gen 4 currently at most. So my question would be is that would a PCIE gen 4 card be able to take advantage of the larger bandwidth of a PCIE GEN 5 slot?
Thoughts or ideas as far as possible Motherboards that I may find compelling?

Will you ever need more than 64GB of ram?

I am going to say right now No, In the future as my interests, and my work changes I do not know, possibly but in the near future I am going to say that 64 gb is ample more than ample.

Okay, if you happened to say yes you’d maybe need to take into consideration which board had a better memory support 128GB is hard to run on am5 currently

yes I have been doing some research on that. As the platform stands right now if you saturate all dimms you are limited to 3600 \but that is still at ddr5 speed and bandwidth. Which is more than lets say ddr4 3600 ddr4 speed and bandwidth, right? or am I missing something>

I think’s about the same bandwidth, but higher latency.

Yes, you’re missing something. Check out CAS latency - Wikipedia

Bandwidth is identical on 3600MT/s the speed depends on the CAS value, which for current versions of DDR4/DDR5 sticks is much faster on DDR4.

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Thanks for the info and link, I now stand a bit more informed :nerd_face:

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Yeah the layout on the ROG STRIX B650E-E GAMING WIFI is a little interesting, and they don’t make it clear up front. As far as I can tell, the two configurations available are basically this:

  1. PCIEX16_1: x16 / PCIEX16_2: none / M.2_3: none
  2. PCIEX16_1: x8 / PCIEX16_2: x4 / M.2_3: yes (x4)

The other 8 PCIe lanes from the CPU are permanently routed to M.2_1 (gen5) and M.2_2 (gen4).

No. The card and slot will settle on the common number of lanes, then common PCIe generation. A gen4 x16 card in a gen5 x4 slot will have gen4 x4 bandwidth available to it.

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I am still going back and forth, I have decided to wait till my case ships to make a decision I am waffling between the asus proart b650 and asus Rog Strix B650E-E gaming wifi. What draws me to these choices 1.dual GPU support 2. ECC memory support. 3. support for a Thuderbolt add in card. I feel that what will sway my decision from one board to another is the pcie lanes accessible after the graphics cards. I am leaning to the Rog Strix B650E-E gaming wifi. I like the out of box IO better than the Asus ProArt b650. Doing a bit of research I wont lose that much bandwidth if I eventually do a dual graphic card setup with x8 x4. and there are more M2 lanes that I can use with an adapter in case I want to expand with another nic or more usb and also can add a thunderbolt card later. also pcie 5 for later gen graphics cards. thoughts? Also is there another board I should be taking a look at that I might have missed.

So, PCIe lanes be like:

Asus ProArt B650 Creator - x8/x8/x1/x4 (though the x1 is directly below second x8, dual GPU does not work) plus Three m.2 with 12 lanes in total. All lanes are PCIe 4.0 except one PCIe 5.0 m.2 in slot 1.

Asus Rog Strix B650-E Gaming Wifi - x8/x8/x4 plus four m.2 slots with 16 lanes (I think one is reroutable from GPU slots). All lanes are PCIe 5.0 except the x4 PCIe slot and last m.2 slot.

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Now here is a questions about physical x16 slots and bifurcation. according to asus official document. [Motherboard] Compatibility of PCIE bifurcation between Hyper M.2 series Cards and Add-On Graphic Cards | Official Support | ASUS Global some of the step down boards such as the x670e- F gaming wife has a physical x16 slot with a bifurcation profile of 4(X4+X4+X4+X4). my question is, in the future if I so decided to expand could I cheat and get a bifurcated riser to split the x16 → x8/x8?

The big difference from ddr4 to ddr5 is that it effectively doubles the number of memory channels. At the same clock rate, it transfers the same amount of data throughput, but much of the time is spent waiting for the next transaction, and ddr5 lets you have two transactions per dimm simultaneously instead of 1 transaction per dimm.

thanks, what are your thoughts on tmy pcie bifurcation question above?

You would need to get a card with a switch/mulitplexer chip. You can’t just wire two x8 cards in to a single x16 slot - there are signals other than the data lanes that have to be handled differently by the PCIe controller (in the CPU) when it’s two slots vs. one.

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Here are some pcie cards with pcie multipliers on them:

Most of those don’t require bifurcation, and give you the benefit of additional pcie lanes.

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One of the weird results of that is now the memory is 32 bit per channel instead of 64

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I’m not sure if that is correct? The manual suggests that bifurcation is supported, so a bifurcated riser should work??

The issue is that PCIe signals at gen 5 speeds travel much harder.

We already have a hard time with PCIe Gen4 risers. Gen 5 risers most likely will require expensive retimers and other stuff to work.

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yeah, so when ddr4 and earlier goes ecc, they go from a multiple of 8 ram chips to a multiple of 9 ram chips.

When ddr5 goes ecc, they go from a multiple of 8 chips, to a multiple of 10 chips. the 8 chips gets broken up into a pair of 4 chips, and each set gets an extra ram chip for ecc.

btw udimms can have ecc on module without providing ecc over the memory bus. This is often to allow the use of sub standard components while still providing a valid service.

I have seen defective memory channels twice in my career which were not caused by bad ram, but by bad motherboards.

So even if the motherboard says it will support ecc udimms, it may save you from bad ram chips, but it will not save you from a failed motherboard trace. about 95% of the time, it is the ram chip which failed, but when it is the motherboard trace, those can be difficult.

in an office with 60 staff and 4 racks of servers, we encountered bad ram about once every month or two, often times it was caught by servers with ecc, sometimes it was tested for on workstations.