AMD Radeon RX 6800 and RX 6800 XT review: A glorious return to high end gaming

Welcome back to the high end, AMD.

Credit: Brad Chacos/IDG

Better with Ryzen: AMD Smart Access Memory

With Ryzen and Radeon finally both firing on all cylinders, AMD decided to unlock capabilities that help the Radeon RX 6000-series achieve even higher frame rates when it’s paired with a Ryzen 5000-series processor in an X570 motherboard.

amd smart access memory AMD

Smart Access Memory gives the CPU full access to the GPU’s memory, rather than limiting it to the usual 256MB chunks. That unrestricted access to the data channel can improve gaming performance. Going off AMD’s numbers, however, the uplift can vary greatly between games, resolutions, and which Radeon RX 6000-series GPU you use.

In the chart below, which AMD included in its reviewers’ guide, Battlefield V and Hitman 2 didn’t get any extra performance at 1080p resolution with Smart Access Memory enabled, but saw a slight uptick as the pixel count moved up. Other games displayed the opposite behavior, delivering a bigger performance uplift at 1080p versus 4K—look at Borderland 3, Resident Evil 3, and Red Dead Redemption 2.

smart access memory AMD

AMD-supplied benchmark data for Smart Access Memory.

It’s interesting how the less-powerful Radeon RX 6800 generally—but again, not universally—tends to see a bigger performance increase with Smart Access Memory enabled, and that all of the games AMD tested use modern “close to the metal” APIs like Vulkan and DirectX 12. None of the games here run on the much more common DirectX 11 API. Are Smart Access Memory’s benefits lessened or negated in DX11? I’d hoped to give the technology a whirl ourselves, but motherboard shipping delays crushed the plans. Stay tuned for a follow-up in the coming days.

Smart Access Memory can’t be used by everyone, though. You need a Ryzen 5000-series processor and a compatible X570 motherboard that has had its BIOS updated to support AMD’s AGESA firmware, along with a current version of Radeon Software (which you need to run the Radeon RX 6800-series anyway) and a 64-bit operating system. For now, X570 motherboards won’t enable Smart Access Memory by default; you need to dive into your BIOS’s advanced settings and activate both “Above 4G Decoding” and “Re-size BAR support” to coax it into working. AMD expects AM4 motherboard makers to turn on Smart Access Memory by default going forward.

AMD Zen 3 Ryzen 5000 Ryzen 9 5900X Ryzen 9 5950X Gordon Mah Ung

You need a Ryzen 5000-series processor like this 5900X to use Smart Access Memory.

Note that terminology—“Re-size BAR support,” and not “Smart Access Memory.” Resizable BAR functionality is part of the PCIe Express specification, but it hasn’t often been used, especially on Windows. Smart Access Memory is basically AMD branding for enabling Resizable BAR with some additional driver optimizations on top. Smart Access Memory serves as a cornerstone for AMD’s “Ultimate Gaming Platform” pitch for pairing Ryzen and Radeon, but if the gains mostly come from resizeable BAR, AMD could activate it on other hardware—and Intel and Nvidia, for that matter.

Nvidia has already reached out to PCWorld to say it's working to enable PCIe Resizeable BAR on its GeForce GPUs, with promising results already in its labs. Nvidia claims the technology works with both PCIe 3.0 and PCIe 4.0, and could work with any processor platform that also supports it. In other words, if Nvidia flipped on resizeable BAR in GeForce cards, it should work with Ryzen 5000 chips just as well as Radeon RX 6000-series GPUs do, unless AMD blocks it in some way.

Don’t let that diminish what AMD accomplished with its “Ultimate Gaming Platform” here, though. Yes, resizeable BAR has been a part of PCIe for a while, but it hadn’t been used before. Enabling the technology requires the processor, motherboard, and graphics card to all join in on the party—something AMD is uniquely positioned to do as a supplier of both CPUs and GPUs. Smart Access Memory should just work when you put a Radeon RX 6800 into a Ryzen 5000 system with a new X570 motherboard. Older X570 motherboards require a BIOS upgrade to get SAM running. If Intel or Nvidia decided to enable Resizeable BAR, it would likely require BIOS updates for all of that hardware as well. While updating your firmware isn’t as scary as it used to be, it’s still far more complicated than simply downloading a new driver.

I wouldn’t be surprised if Nvidia and Intel indeed supported Resizeable BAR in the future now that AMD's dragged it into the light. But expect Smart Access Memory to be a key AMD advantage until its rivals start enabling it by default.

Enough scene-setting. Let’s get to the benchmarks.

Next page: Our test system, gaming benchmarks begin

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Brad Chacos

Brad Chacos

PC World (US online)
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