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Intel Alder Lake PCIe 5.0 Configuration Reportedly Detailed In Coreboot

PCIe Interface
(Image credit: Shutterstock)

Alder Lake won't just be the first to bring an x86 hybrid architecture to desktops; the processors have also been pegged to leverage the high-velocity PCIe 5.0 interface. Coreboot (via Komachi_Ensaka), an open-source substitute for UEFI, seems to contain valuable information on the potential PCIe configuration that we could see on Alder Lake.

Early rumors claimed that the 12th Generation Alder Lake processors would support both the PCIe 5.0 and PCIe 4.0 standard, and Tim Wawrzynczak's assessment of the code seems to confirm that. However, the code specifically references Alder Lake-P (ADL-P), so it's uncertain if the same setup will translate over to the Alder Lake-S lineup. We still have no idea what Alder Lake-P will be, but some think it could be Intel's Atom P-series or a mobile chip. In any event, a previous coreboot patch revealed that Alder Lake-P could max out at 14 cores, six Golden Cove cores, and eight Gracemont cores.

Alder Lake-P appears to provide a flexible PCIe layout. The processor reportedly offers one PCIe 5.0 x8 lane or two PCIe 4.0 x4 lanes. The PCIe 5.0 lane has no problem running at x4. It would appear that neither interface supports bifurcation, meaning you can't split up the PCIe 5.0 lane or get the PCIe 4.0 lanes to operate at x8. Nonetheless, both are backward compatible with previous-gen devices.       

Interfacex16x8x4x2x1
PCIe 5.064 GBps32 GBps16 GBps8 GBps4 GBps
PCIe 4.032 GBps16 GBps8 GBps4 GBps2 GBps
PCIe 3.016 GBps8 GBps4 GBps2 GBps1 GBps
PCIe 2.08 GBps4 GBps2 GBps1 GBps0.5 GBps
PCIe 1.04 GBps2 GBps1 GBps0.5 GBps0.25 GBps

A single PCIe 5.0 x8 lane might sound lackluster at first, but it actually provides plenty of bandwidth. PCIe 5.0 x8 is essentially equivalent to PCIe 4.0 x16; therefore, the interface is good for up to 32 GBps of bandwidth, which is more than any consumer PCIe-based device can consume.

Only AMD's Ryzen 3000 and Ryzen 5000 mainstream processors have embraced the PCIe 4.0 standard on a desktop platform at this point. Intel's imminent Rocket Lake should change that panorama. 

There are quite a few mainstream PCIe 4.0 products, including graphics cards and M.2 SSDs, on the market right now. Tests have shown that even the fastest graphics cards have yet to saturate a PCIe 3.0 x16 interface, much less PCIe 4.0. M.2 SSDs, on the other hand, have been able to exploit the extra bandwidth that PCIe 4.0 brings to the table. We expect the PCIe 5.0 situation to play out the same.

  • JayNor
    "Only AMD's Ryzen 3000 and Ryzen 5000 mainstream processors have embraced the PCIe 4.0 standard at this point."

    Tiger Lake-U chips have PCIE4
    Reply
  • JayNor
    "We expect the PCIe 5.0 situation to play out the same."

    PCIE5 doubles the max bandwidth per lane, so perhaps a single lane would do for a PCIE5 SSD and perhaps 3 lanes would do for a GPU.

    I suspect Intel wants to use the PCIE5 to show off CXL performance increases for GPUs, since that is what they have announced with the Sapphire Rapids Server chips.
    Reply
  • JayNor
    "It would appear that neither interface supports bifurcation, meaning you can't split up the PCIe 5.0 lane or get the PCIe 4.0 lanes to operate at x8."

    PCIE5 is backwards compatible with all prior pcie versions. It starts negotiations at PCIE1.

    The patch comments also explicitly say that the 8 lanes of PCIE5 can be split into two groups of 4 lanes.
    Reply
  • InvalidError
    the interface is good for up to 32 GBps of bandwidth, which is more than any consumer PCIe-based device can consume.
    I could imagine a low-end GPU needing to use system RAM to supplement its 4-6GB of VRAM using a good chunk of that 32GB/s. That's where the 4GB RX5500 gets its huge 4.0x8 vs 3.0x8 boost (closes 70-80% of the gaps with the 8GB variant) from. I count that as at least one thing in consumer space that could significantly benefit from it as soon as lower-end 5.0x8 GPUs become available.
    Reply
  • JOSHSKORN
    Would be great if my 6 year old PC holds out until PCI-e 5.0 appears on intel motherboards. Maybe by then, they'll have a GPU available that is actually noticeably hindered by PCI-e 3.0. From what I've seen, even with the RTX 3090, there's literally only a couple of FPS difference in performance between PCI-e 3.0 and PCI-e 4.0.
    Reply
  • InvalidError
    JOSHSKORN said:
    From what I've seen, even with the RTX 3090, there's literally only a couple of FPS difference in performance between PCI-e 3.0 and PCI-e 4.0.
    With the 4GB RX5500, 4.0x8 vs 3.0x8 can make the difference between 40fps and 70fps whereas the 8GB variants score 80fps regardless, almost making the 8GB models unnecessary. Had the RX5500 had a 4.0x16 interface, the 8GB models' VRAM size advantage would have been mostly irrelevant.

    People keep gawking over the high-end but it is the lower-end GPUs that would benefit the most from 5.0x16 on a DDR5 platform once the parts become affordable.
    Reply
  • Tom Sunday
    Alder Lake: One of the most significant architectural upgrades in
    INTEL's generations. The new 12th generation CPU is also much larger than any socket Intel ever pushed into the mainstream. The 'rectangular' looking socket dimensions for LGA 1700 will be 37.5mm x 45mm, which is about 7.5mm taller than Intel's current LGA 1200. Does this mean that my newly purchased "Corsair Capellix" for $170 is outdated and needs scrapping if I want to fly or upgrade to Alder Lake in the fall of 2021? A new AIO's supposed to give anyone 5-years of sterling service. Surely my new Capellix AIO footprint will not cover or adequately cool the new much larger upcoming LGA 1700. What gives?
    Reply
  • InvalidError
    Tom Sunday said:
    Surely my new Capellix AIO footprint will not cover or adequately cool the new much larger upcoming LGA 1700.
    The only area of the IHS that really needs to make contact with the HSF or cooling block is the area surrounding the cores and that area is only a small fraction of the total IHS surface. As long as your AiO's manufacturer makes an updated bracket to locate the block over the correct spot, you'll be fine.
    Reply
  • Tom Sunday

    post: 22139330 As long as your AiO's manufacturer makes an updated bracket to locate the block over the correct spot said:

    I wonder if Corsair will actually offer all 'Alder Lake' upgraders a free (or at a reasonable cost) CPU block retrofit? The H150i Elites pump head comes with 33 Capellix LEDs for the full RGB experience and with non detachable tubing. Looking back I am now disapointed that Corsair (being a major connected hardware player) when I first purchased the AIO this past November, did not make any mention of a possible late 2021 'die-change' and thus coming clean with all purchasers. They should have known. Perhaps even offering as part of 'Buying Now' upcoming CPU block fixes. I must be one of many thousands sitting with relatively newly purchased AIO's that will have the same problem and with all other AIO vendors out there.
    Reply
  • JayNor
    At CES 2021, Intel gave a sneak peek at a desktop PC running Windows on an Alder Lake chip ... They also said these are coming in 2H 2021. The slide in that presentation indicated Alder Lake versions will exist for both mobile and desktop, which confirms rumors.
    Reply