PCIe 4.0

As the first commerical x86 server CPU supporting PCIe 4.0, the I/O capabilities of second generation EPYC servers are top of the class. One PCIe 4.0 x16 offers up to 32 GB/s in both direction, so each socket offers up to 256 GB/s in both directions, for a full 128 PCIe 4.0 lanes per CPU. 

Each CPU has 8 x16 PCIe 4.0  links available which can be split up among up to 8 devices per PCIe root, as shown above. There is also full PCIe peer-to-peer support both within a single socket and across sockets.

With the previous generation, in order to enable a dual socket configuration, 64 PCIe lanes from each CPU were used to link them together. For EPYC, AMD still allows for 64 PCIe lanes to be used, but these are PCIe 4.0 lanes now. There is also another feature that AMD has here - socket-to-socket IF link bandwidth management - which allows OEM partners to design dual-socket systems with less socket-to-socket bandwidth and more PCIe lanes if needed. 

We also learned that there are in fact 129 PCIe 4.0 lanes on each CPU. On each CPU there is one extra PCIe lane for the BMC (the chip that controls the server). Considering we are living in the age of AI acceleration, the EPYC 7002 servers will be great as hosts for quite a few GPUs or TPUs. Density has never looked so fun.

Zen 2 and Rome: SMILE For Performance The BIG LIST of Rome CPUs: Core Counts and Frequencies
Comments Locked


View All Comments

  • Zoolook - Saturday, August 10, 2019 - link

    It's been a pretty good investment for me, bought at 8$ two years ago, seems like I'll keep it for a while longer.
  • CheapSushi - Wednesday, August 7, 2019 - link

    It's glorious...one might say.... even EPYC.
  • abufrejoval - Wednesday, August 7, 2019 - link

    Hard to believe a 64 core CPU can be had for the price of a used middle class car or the price of four GTX 2080ti.

    Of course once you add 2TB of RAM and as many PCIe 4 SSDs as those lanes will feed, it no longer feels that affordable.

    There is a lot of clouds still running ancient Sandy/Ivy Bridge and Haswell CPUs: I guess replacing those will eat quite a lot of chips.

    And to think that it's the very same 8-core part that powers the engire range: That stroke of simplicity and genius took so many years of planning ahead and staying on track during times when AMD was really not doing well. Almost makes you believe that corporations owned by share holders can actually sometimes actually execute a strategy, without Facebook type voting rights.

    Raising my coffee mug in a salute!
  • schujj07 - Thursday, August 8, 2019 - link

    Sandy Bridge maxed out at 8c/16t.
    Ivy Bridge maxed out at 15c/30t.
    Haswell maxed out at 18c/36t.
    That means that a single socket Epyc 64c/128t can give you more CPU cores than a quad socket Sandy Bridge (32c/64t) or Ivy Bridge (60c/120t) and only a few less cores that a quad socket Haswell (72c/144t).
  • Eris_Floralia - Wednesday, August 7, 2019 - link

    This is what we've all been waiting for!
  • Eris_Floralia - Wednesday, August 7, 2019 - link

    Thank you for all the work!
  • quorm - Wednesday, August 7, 2019 - link

    Given the range of configurations and prices here, I don't see much room for threadripper. Maybe 16 - 32 cores with higher clock speeds? Really wondering what a new threadripper can bring to the table.
  • willis936 - Wednesday, August 7, 2019 - link

    A reduced feature set and lower prices, namely.
  • quorm - Wednesday, August 7, 2019 - link

    Reduced in what way, though? I'm assuming threadripper will be 4 chiplets, 64 pcie lanes, single socket only. All ryzen support ecc.

    So, what can it offer? At 32 cores, 8 channel memory becomes useful for a lot of workloads. Seems like a lot of professionals would just choose epyc this time. On the other end, I don't think any gamers need more than a 3900x/3950x. Is threadripper just going to be for bragging rights?
  • quorm - Wednesday, August 7, 2019 - link

    Sorry, forgot to add, 3950x is $750, epyc 7302p is $825. Where is threadripper going to fit?

Log in

Don't have an account? Sign up now