AMD RX 6700 XT review: Resizeable BAR testing

Like the other Radeon RX 6000-series cards we tested earlier, the RX 6700 XT supports Smart Access Memory, AMD's branded implementation of the PCI Express Resizeable BAR feature. This tech allows all 12GB of video memory on the RX 6700 XT to be directly accessed by the CPU, rather than via a 256MB I/O buffer.

This improved access can boost frame-rates substantially in some games, but requires a relatively recent motherboard with a BIOS update to engage the feature. For our testing, we're using a Z490 board that has received the update, the Asus Maximus 12 Extreme.

Assassin's Creed Valhalla

Assassin's Creed Valhalla is a new one for the Digital Foundry graphics test suite, but already the game looks promising. As well as showing stark differences between Resizeable BAR enabled versus disabled at all three resolutions we tested, the game also exhibits less CPU bottlenecking at lower resolutions compared to its predecessor, Assassin's Creed Odyssey. The RX 6700 XT sees a 12 per cent performance improvement from ReBar being enabled at 1080p, dropping to nine per cent at 1440p and three per cent at 4K.

Battlefield 5

Battlefield 5 is up next. The game runs well with RT disabled on the RX 6700 XT even at 4K, but you'll see modest gains throughout when Resizeable BAR is enabled. We measured a two per cent improvement at 1080p, seven per cent at 1440p and five per cent at 4K. This isn't enough to really change the game's performance profile on the RX 6700 XT, but it's still a welcome boost.

Borderlands 3

We'll conclude with Borderlands 3. Here, we see the greatest improvements from Resizeable BAR at Full HD, where the improvement is a healthy 13 per cent, Quad HD is eight per cent and Ultra HD is just four per cent. Still, it's well worth upgrading your motherboard to a BIOS version that supports Resizeable BAR if it's available.

So on each of these three titles, we're seeing anywhere from a marginal to a very healthy advantage from enabling Smart Access Memory on the RX 6700 XT, so it's certainly worth enabling if your combination of CPU, GPU and motherboard allows it.

All AMD 500-series and Intel 500-series motherboards going forward should support the feature, but selected models from the last generation (or two) may also have new BIOS versions available that support Resizeable BAR when paired with a recent processor, such as the Asus Z490 board we're testing with. If you're not sure if your motherboard is among them, it's best to check the manufacturer's website for your particular motherboard model, then check the BIOS section of the Support or Downloads page to see if Resizeable BAR or Smart Access Memory is listed in the update notes.

Once your BIOS is updated, you should be able to find and enable 'Above 4G decoding' somewhere in the BIOS' advanced PCIe or I/O settings. This in turn should show the option for 'Resize BAR Support'; enable that and you should be off to the races. As well as the motherboard and processor requirements, you'll need to have a 64-bit OS (which should be just about everyone these days), be running Radeon 20.11.2 or newer and have legacy boot (CSM) disabled in your BIOS.

With the feature becoming more common on both AMD and Intel's latest motherboard platforms, all we really need at this stage is a greater number of games that are proven to take advantage of the feature. Right now, AMD gives the following game list in the Smart Access Memory section of their reviewer's guide:

Nvidia's list of games with Resizable BAR support also includes Forza Horizon 4, Metro Exodus and Watch Dogs Legion, so it's possible that these games will also exhibit increased performance with Smart Access Memory enabled on Radeon RX 6000-series GPUs too.

Hopefully, we'll see these lists lengthen over time, as more games are able to be tested and whitelisted, as having that extra five to 15 per cent performance is a nice bonus.

AMD Radeon RX 6700 XT Analysis

• Introduction, Hardware and Power Analysis
• Doom Eternal, Control, Borderlands 3, Shadow of the Tomb Raider - Game Benchmarks Part 1
• Death Stranding, Far Cry 5, Hitman 2, Assassin's Creed Odyssey - Game Benchmarks Part 2
• Metro Exodus, Dirt Rally 2, Assassin's Creed Unity, Assassin's Creed Valhalla - Game Benchmarks Part 3
• RT Game Benchmarks - Control, Metro Exodus, Battlefield 5
• Resizeable BAR Testing - Watch Dogs Legion, Battlefield 5, Metro Exodus [This Page]
• AMD Radeon RX 6700 XT - the Digital Foundry verdict