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AMD Ryzen 4000 Renoir: PCIe 4.0 Support Looking Less Likely

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Biostar B550 motherboard listing is telling

Biostar Racing B550GTA

Biostar Racing B550GTA (Image credit: Biostar)

The possibility of PCIe 4.0 support on the upcoming AMD Ryzen 4000-series (codename Renoir) desktop APUs isn't looking too good. Looking at the product page for the Biostar Racing B550GTA motherboard, you'll see notes clearly stating that PCIe 4.0 support "depends only on Ryzen 3rd Gen Matisse" and "PCIe 4.0 speed only for AMD Ryzen 3rd Gen Matisse." 

Many rumors about AMD's Renoir APUs have surfaced over recent weeks. In a nutshell, the Ryzen 4000-series could span up to eight Zen 2 CPU cores with Vega Compute Units (CUs) that scale up to to 2,100 MHz. One leak has claimed that Renoir will feature a 2,000 MHz Fabric Clock (FCLK), meaning we could see the APUs leverage DDR4 RAM modules up to 4,000 MHz.

But nothing we've heard so far has hinted at whether or not Renoir will adopt the PCIe 4.0 interface. 

Although, the mobile Ryzen 4000-series chips debuting with PCIe 3.0 support may have been a clue. AMD made a rather convincing statement on why mobile Ryzen 4000-series parts retained support for PCIe 3.0. The chipmaker intentionally excluded PCIe 4.0 support in favor of power reduction. Power consumption shouldn't be a big concern on a desktop chip, but to bring PCIe 4.0 support to Renoir would require AMD to draft up an additional new design. In all likelihood, the desktop variant will use identical silicon to what's inside the mobile variants. 

Similar to the previous generation of APUs, Renoir will seemingly continue to be stingy on the PCIe lanes. The Racing B550GTA's specification table says that Renoir will only provide eight PCIe lanes to the primary PCIe x16 slot. Therefore, graphics cards are limited to half the available bandwidth on the slot. 

APUs target shoppers with tight budgets who aren't likely to purchase a discrete graphics card. Therefore, if Renoir does arrive without PCIe 4.0 support and with limited PCIe lanes, it shouldn't be a deal breaker for the chips' intended market. 

On the other hand, an APU owner is more likely to pick up a PCIe 4.0 SSD. These SSDs aren't cheap yet, but have become a lot more accessible. So it would be nice if Renoir did debut with some sort of PCIe 4.0 support, even it's just for the M.2 slots.

7 Comments Comment from the forums
  • RodroX 22 May 2020 10:32
    I believe thats ok, anyone looking for an APU is probably needing a good CPU performance for basic/medium office/content creation tasks and/or the best integrated GPU for gaming in a very tight budget (with the posibility to add a discret graphic card later on).

    I don't think the lack of PCIe 4.0 will be a huge thing for any of those buyers. They wont be going for an RTX 2080TI or whatever comes later in the very high end. Is not like an RTX 2080TI can saturate PCIe 3.0 anyways.
    Reply
  • Red Ninja Dolphins 22 May 2020 11:24
    ASRock effectively confirms that Renoir is PCIe 3.0 only in their B550 board specs, such as this one: https://www.asrock.com/mb/AMD/B550 Taichi/index.asp#Specification
    Quote (emphasis mine):

    AMD Ryzen series CPUs (Matisse)
    - 3 x PCI Express x16 Slots (PCIE1/PCIE3/PCIE5: single at Gen4x16 (PCIE1); dual at Gen4x8 (PCIE1) / Gen4x8 (PCIE3); triple at Gen4x8 (PCIE1) / Gen4x8 (PCIE3) / Gen3x4 (PCIE5))*

    AMD Ryzen series APUs (Renoir)
    - 3 x PCI Express x16 Slots (PCIE1/PCIE3/PCIE5: single at Gen3x16 (PCIE1); dual at Gen3x8 (PCIE1) / Gen3x8 (PCIE3); triple at Gen3x8 (PCIE1) / Gen3x8 (PCIE3) / Gen3x4 (PCIE5))

    I wouldn't be surprised if this gets taken down at some point, mind, as AMD hasn't even announced AM4 Renoir.

    To me personally, as someone in the market for an 8-core APU, this is fine. (I'm keen to upgrade from my 2400G) If anything, not having to take the substantial hit on idle power draw is an upside. To me, B550 finally supporting PCIe 3.0 on (some of) the chipset-attached slots (rather than 2.0 in the 300 and 400 series chipsets) is more important.
    Reply
  • digitalgriffin 22 May 2020 13:49
    All of Ryzen APUs starting with Raven Ridge have cut down pcie lanes. The south bus chipset always operates 1 pcie gen behind. So this shouldnt be a surprise.

    It is possible a plux chip could be used by taking 2x4 pcie3 and make them 1x4 pcie4. But this has its own drawbacks.
    Reply
  • alextheblue 22 May 2020 23:42
    One leak has claimed that Renoir will feature a 2,000 MHz Fabric Clock (FCLK), meaning we could see the APUs leverage DDR4 RAM modules up to 4,000 MHz.
    I mean, you can already do this (and beyond) by changing the fclk mclk ratio, even if I wouldn't necessarily recommend that for performance reasons. So it's not like high clocked RAM support is new to Zen 2. Being able to run them that high 1:1 would be better (or possibly decoupling the IF like Renoir), but I don't think you're going to make massive gains over 3600 in either case. Well, outside of the iGPU, which isn't latency sensitive in the first place (and thus would be happy even at 2:1, bandwidth is king).

    Even if the gains are larger than anticipated, the price is so much higher for decent RAM beyond 3600, so I don't think you'll see a lot of people taking advantage.
    Reply
  • msroadkill612 23 May 2020 13:42
    Sadly, it rings true. A big thing for AMD, is for one design to have wide use. An APU will always have a weather eye on the lower power envelope of mobile.
    Reply
  • msroadkill612 23 May 2020 13:53
    alextheblue said:
    I mean, you can already do this (and beyond) by changing the fclk mclk ratio, even if I wouldn't necessarily recommend that for performance reasons. So it's not like high clocked RAM support is new to Zen 2. Being able to run them that high 1:1 would be better (or possibly decoupling the IF like Renoir), but I don't think you're going to make massive gains over 3600 in either case. Well, outside of the iGPU, which isn't latency sensitive in the first place (and thus would be happy even at 2:1, bandwidth is king).

    Even if the gains are larger than anticipated, the price is so much higher for decent RAM beyond 3600, so I don't think you'll see a lot of people taking advantage.
    "the price is so much higher for decent RAM beyond 3600"

    maybe, but kinda flawed logic imo... we see the same ram working better as zen & am4 improved.

    ie. maybe 3600+ ram is dear cos its hard to get higher on current rigs?
    Reply
  • alextheblue 23 May 2020 19:20
    msroadkill612 said:
    "the price is so much higher for decent RAM beyond 3600"

    maybe, but kinda flawed logic imo... we see the same ram working better as zen & am4 improved.

    ie. maybe 3600+ ram is dear cos its hard to get higher on current rigs?
    It's actually easy to hit >3600 on recent OC-capable Intel platforms, and pretty much any Zen 2. You don't see it often, because the minor gains aren't worth the increase in price. The money would be FAR better sunk into other components, until you're in the very high-end. Then you simply start to run out of other things to improve.

    For Zen 2 in particular, the IMC was improved, and now you can set an MCLK : FCLK divider to 2:1. That wasn't even an option for Zen 1 / 1+. But doing so will actually hurt performance in most tasks until you hit some REALLY high speeds, like ~4200+. You can also exceed 3600 even at 1:1 ratio by overclocking the IF, but even then 3733 and 3800 still isn't generally worth it.

    So again this is NOT the first Zen to be able to hit those high speeds, and even though they've decoupled the IF from the memory clock, it won't really matter all that much. The gains above 3600 even at 1:1 weren't that great to start with on the CPU side. The area where you would see the most gains is the iGPU, and graphics performance isn't latency sensitive in the first place so even if you had a coupled IF at 2:1 it wouldn't hurt it.

    With that being said, a theoretical decoupled IF and high memory clocks might be more interesting for a 16 core Zen 3, for some workloads.
    Reply