One of the most interesting technologies from AMD’s recent GPU launch was Smart Access Memory. It’s a feature that’s part of the PCI express standard that required all-AMD hardware to work. And while it wasn’t useful in all scenarios, there are a number of games where SAM makes a difference. And if you’re an Nvidia owner feeling sad about missing out on fancy new features, don’t worry: your own version of SAM is arriving in the next couple of months.
Amidst all the CES 2021 bluster today, Nvidia confirmed via a separate blog post that resizeable BAR support would be added with the release of the RTX 3060 in late February. Existing RTX cards will get resizeable BAR too — on AMD and Intel platforms, so nobody’s missing out — but those firmware updates won’t ship until later:
For desktop systems to get the benefits of Resizable BAR, you will need a graphics card, motherboard and graphics driver that support the feature. New GeForce RTX graphics cards starting with the GeForce RTX 3060 will have support for Resizable BAR. NVIDIA and our GPU partners are also readying VBIOS updates for existing GeForce RTX 30 Series graphics cards starting in March.
Resizable bar is basically a function within the PCI Express standard that increases the buffer between the CPU and the GPU. The CPU constantly passes geometry, shaders and textures to the GPU over the course of a game, but current limitations mean there is only a very small amount of memory — 256MB to be precise — that the CPU can access.
AMD’s Smart Access Memory — and resizable BAR support — basically unlocks that, allowing the CPU direct access to the entirety of the RAM on your graphics card. It’s a very new feature, and as a result there are tons of games that don’t really see any benefit from the increased bandwidth.
However, there are a few games that do see a noticeable jump. Forza Horizon 4 is the biggest outlier at the moment, with most testing finding at least a 10 percent improvement when SAM (AMD’s deployment of the resizable BAR feature) is enabled. Assassin’s Creed Valhalla and Borderlands 3 are two other games with impressive gains at lower resolutions, too. But most games only see performance gains of a few percent, and there are cases where performance is actually worse, like Microsoft Flight Simulator and Apex Legends which really struggled.
But it’s hard to complain in the end, because there is a marginal improvement in a good chunk of games — and it’s performance that’s available literally by enabling a setting in your motherboard BIOS. And once this becomes standardised, bigger performance gains might be possible. A lot of the games tested in Hardware Unboxed’s 36-game round-up are all fairly modern — Godfall, DiRT 5, Borderlands 3, Assassin’s Creed: Valhalla and Resident Evil 3 are all less than 12 months old. And at 1080p and 1440p, 20 and 21 of the games tested got some performance benefit from SAM being enabled (and you can imagine the biggest negative outliers would be something that developers could correct in the future with patches).
All in all, you have to thank AMD’s competition for this one. Who doesn’t like potentially free performance gains? Sure, it might not be a huge amount in some cases. But free is still free. Now, how’s that open-source super sampling (read: a DLSS alternative) technique from AMD doing?
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