AMD X590 Chipset Pops Up Again - 24 Full PCIe 4.0 lanes instead of 16?
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Silva
All I wanted was B550, that only comes in Q1 2020...
I'll have to get B450 probably.
MBTP
Funny, no one even thought about dual socket...
Quite a feaseable approach.
schmidtbag
MBTP
schmidtbag
https://www.newegg.com/p/N82E16819113470
https://www.newegg.com/p/N82E16819113469
Both CPUs are nearly identical. They have pretty much all the same specs, they're the same generation, same everything. Both models will work in any Epyc-compatible motherboard [alone]. And yet, the non-P model is $1300 more expensive. What's the difference you might ask? The 7551 can be paired up with another 7551 in a dual-socket motherboard, whereas the P model can't. Why? because the on-die chipset is different.
What this means is whether you're going for AM4 or TR4, you can't just slap in a new/better chipset and another CPU socket. The CPUs themselves determine whether they can be paired up. I'm quite confident this is no different for Intel.
In the case of Epyc, I'm not sure if there's actually a physical difference between the P and non-P models (or if it's just a firmware difference), but my point is Epyc was built with multi-socket in mind and the CPUs themselves are now what determines whether they can be paired up or not. AM4 was never built with this capability, and therefore, it isn't physically possible to have multiple AM4 sockets interconnected on a single motherboard.
Besides, I don't really see what the reason for a multi-socket AM4. Might as well just go for Threadripper or Epyc for what would likely cost roughly the same.
A high-end chipset doesn't mean it will support multi-socket boards. I will bet you your dream PC that a dual-socket AM4 motherboard will never happen.
Ever noticed there's no longer a "northbridge" in modern PC motherboards? That's because they're integrated into the CPU package. Back in the old days when there were external northbridges, they controlled pretty much everything, and were the central hub of communication. If you wanted a multi-socketed motherboard back then, you needed one with a northbridge that was capable of it.
That doesn't apply anymore.
Now that it's integrated into the CPU, you can't swap it out. Today's "northbridges" (for lack of a better term) has a pre-determined set of functions and you're stuck with them. For desktop parts like AM4 and 1151, none of those CPUs were designed to be capable of multi-socket setups.
You might be thinking "what about the chipset on the motherboard" but that's basically what the old southbridge used to be. It still for the most part functions the same way, maybe taking on a few extra responsibilities here and there. In modern motherboards capable of multi-socket CPUs, that chipset ("southbridge") isn't what makes that happen.
To further emphasize my point, consider these 2 products:
MBTP
DmitryKo
There is no immediate need for dual socket on the desktop, when a single AM4 socket holds full 16 SMT cores in a multi-chip package for Ryzen 9 3850X (and a single TR4 socket would hold up to 64 SMT cores in the upcoming Threadripper 3000 series), with fast on-die links for cache coherent NUMA access to local memory.
Multi-socket motherboard would make sense for cloud servers, which have to pack a single rack unit with as many CPU dies and gigabytes of DRAM as it is physically possible; and even then, each socket (i.e. multi chip package) has its own local memory, and far (inter-socket) memory access performance is only a fraction of near (on-die) performance.
user1
schmidtbag
user1
https://www.servethehome.com/why-amd-epyc-rome-2p-will-have-128-160-pcie-gen4-lanes-and-a-bonus/
as for extra pins, you can estimate this from other sockets plus the fact zen is basically an soc, all of the pins are for either pcie , usb, power and dram, that and most if not all sockets have reserved pins for debug or future use.
There was also the z490 chipset which was cancelled, but confirmed to exist by board oems last year, that would have added more pcie lanes.
AMD uses pcie lane phys for its Xgmi interconnect on its 2p(dual socket) epyc servers, they use the exact same dies as zen 1, it was designed to do this.
schmidtbag
user1
DmitryKo
On Socket AM4, only 47 (forty seven) pins are RSVD (reserved - not connected) , and 22 of them are located immediately around VDDP pins (+5V power rail) - so it is unlikely these can be reassigned as additional PCIe pins.
On the contrary, Socket TR4 has 902 (nine hundred and two) RSVD pins, of which the I/O area has a total of 240 RSVD pins pre-arranged and interspersed with Vcc/GND to double the number of existing PCIe lanes from 64 to 128 on the Socket SP3 EPYC processors, and the remaining pins are used to double memory channels from 4 to 8.
https://drive.google.com/drive/folders/1L_B4ltl-JCg7S3Hg2OfsoPKIIBXOTXZG