Resizable BAR Explained: What It Is and How to Enable It

Resizable BAR (ReBAR) is a PCI Express feature that lets your processor see and address a graphics card's video memory in one contiguous block, rather than being capped at 256MB chunks at a time. AMD markets the same underlying capability as Smart Access Memory (SAM); ASRock calls its version Clever Access Memory (CAM); Intel and Nvidia both just call it Resizable BAR. It is not a new GPU architecture or a marketing gimmick exclusive to one vendor — it is a standard PCIe capability that any sufficiently modern CPU, motherboard, and GPU can support together, and turning it on is mostly a BIOS checkbox.

What Resizable BAR actually is

Every PCIe device, including a graphics card, exposes part of itself to the rest of the system through Base Address Registers (BARs). A BAR tells the CPU "here is a block of my memory you can map into your own address space and talk to directly." According to Wikipedia's PCI configuration space article, a PCI function can implement up to six BARs, and classically each one was capped at a maximum useful size well below a modern GPU's framebuffer — in practice, graphics drivers historically exposed only a 256MB window onto VRAM, even on cards with 8, 12, or 16GB of memory on board.

That mismatch mattered because every time the CPU needed to push something into VRAM that fell outside the current 256MB window — a texture, a geometry buffer, shader data — the system had to do extra work to move the window or route the transfer indirectly. Resizable BAR is the mechanism that lets a PCIe device negotiate a much larger BAR size at boot, so the CPU can address the GPU's entire frame buffer as one block. Intel's own support documentation describes it plainly: Resizable BAR "allows the PCIe device, such as a discrete graphics card, to negotiate the BAR size to optimize system resources," and enabling it "can result in a performance improvement."

How it works, in practical terms

With Resizable BAR off, the CPU and GPU driver have to manage data transfers in and out of that small 256MB window, which adds overhead — effectively more trips, more bookkeeping, more waiting — especially for games and applications that stream large amounts of texture or geometry data in and out of VRAM each frame. With it on, the CPU can address the whole framebuffer directly, which means fewer, larger transfers instead of many small staged ones. Nvidia's own description of the feature for GeForce RTX 30 Series cards frames it the same way: rather than sending many small requests for textures, shaders, and geometry, data can be requested as needed and sent in full, and multiple requests can transfer at the same time instead of queuing one after another.

Nothing about this changes how much VRAM your card has — Resizable BAR doesn't add memory, it changes how efficiently the CPU can reach the memory that's already there. If you're trying to figure out how much VRAM you actually need for the games or workloads you run, that's a separate question worth answering on its own, covered in Pandromeda's guide to how much VRAM you need in 2026.

AMD Smart Access Memory vs Nvidia and Intel's "Resizable BAR"

The naming split traces back to how each company introduced the feature to a mainstream audience. AMD launched its Ryzen 5000 + Radeon RX 6000 platform in late 2020 under the brand Smart Access Memory, initially presenting it as a benefit of pairing AMD CPUs with AMD GPUs. AMD has since clarified that SAM is its name for enabling the underlying PCI-SIG Resizable BAR capability — its own smart-technologies page describes Smart Access Memory as giving AMD Ryzen processors "immediate, full access to AMD Radeon graphics memory for faster data transfers between the two." Nvidia rolled out support for its RTX 30 Series shortly after, under the generic "Resizable BAR" name, and Intel uses the same generic term across its Arc GPU documentation. ASRock's "Clever Access Memory" is simply that motherboard vendor's own label for the BIOS option on some of its boards.

Functionally, by 2026 this distinction mostly doesn't matter for buying decisions: Resizable BAR support is effectively standard across current Intel, AMD, and Nvidia GPUs, and across any reasonably recent motherboard chipset. The naming is a historical artifact of the marketing split, not a sign that one vendor's version is technically different from another's.

What you need for it to actually work

Resizable BAR is a three-way handshake. All three pieces have to support it at the same time, or it silently stays off (or your system reports it as unsupported) even though any individual component "supports" it on a spec sheet:

• CPU: needs to be recent enough to sit on a platform whose chipset and firmware expose the option.
• Motherboard: needs a BIOS/UEFI build that includes the Resizable BAR / Above 4G Decoding toggles, and typically needs CSM (Compatibility Support Module)/Legacy boot mode disabled in favor of pure UEFI boot.
• GPU and driver: the graphics card's firmware (VBIOS) and the installed driver both need to support negotiating a larger BAR.

Two details that trip people up. First, integrated graphics on the CPU has no bearing on Resizable BAR for a discrete GPU — Intel's own compatibility notes specifically point out that a CPU with no integrated graphics at all still supports the feature fine, as long as the platform otherwise qualifies. Second, not every CPU-and-chipset combination listed as "compatible" performs identically: Intel's own platform guidance flags that some lower-end APUs (like the Ryzen 5 8500G) only expose four PCIe lanes to the GPU slot, which caps the benefit even with Resizable BAR enabled.

How to turn it on in BIOS

The exact menu wording varies by motherboard vendor, but the steps are consistent across Intel and AMD platforms:

1. Reboot and enter BIOS/UEFI setup (commonly Del or F2 at startup — check your board maker's manual if neither works).
2. Make sure your boot mode is UEFI, not Legacy/CSM. If there's a "CSM Support" or "Legacy Mode" toggle, disable it.
3. Find and enable Above 4G Decoding (sometimes called "Above 4G MMIO" or similar). Save this change — on some boards the Resizable BAR option only appears after Above 4G Decoding has been saved and the BIOS screen is reopened.
4. Find and enable Re-Size BAR Support (it may instead be labeled Smart Access Memory or Clever Access Memory depending on your board). If "Enabled" isn't an available choice, try "Auto."
5. Save changes and exit, then boot into Windows (or your OS of choice).
6. Confirm it actually took: Intel systems can check via Intel Driver & Support Assistant; AMD systems can check in AMD Software: Adrenalin Edition under the Performance/Tuning section; Nvidia's control panel and GPU-Z (a widely used third-party utility) also report BAR status for Nvidia and other cards.

If you're building or upgrading a system specifically to take advantage of this plus faster PCIe lanes generally, it's worth understanding what's coming down the pipe at the slot level too — see Pandromeda's explainer on PCIe 6.0 speeds and when they reach desktops for where PCIe bandwidth is headed next.

Is it actually worth turning on?

Mostly yes, but temper your expectations. The honest picture, pieced together from the vendors' own materials: Nvidia's description says Resizable BAR "can increase performance in games," without committing to a number, because the effect depends heavily on the specific game engine and how it streams assets. AMD's own smart-technologies page says Smart Access Memory "unlocks higher performance across select titles" — the key word being "select." Neither company publishes a blanket average improvement figure, and for good reason: independent testing around the RX 6000 and RTX 30 launches consistently found some titles gaining noticeably while plenty of others showed effectively no change, and a small number even regressed slightly. That pattern has held up as the feature became standard rather than a novelty.

In other words, Resizable BAR is not a universal frame-rate unlock. It's a low-level data-path optimization that some game engines are positioned to benefit from and others simply aren't. If your CPU, board, and GPU all already support it, there's essentially no downside to leaving it on — it isn't a trade-off against stability or power draw in any meaningful way for most setups — so the practical answer is "leave it enabled and don't expect it to be the reason your frame rate changed." It is not a substitute for having enough VRAM or PCIe bandwidth in the first place, and it won't rescue a GPU that's simply underpowered or bottlenecked elsewhere, including setups built around external GPU enclosures over Thunderbolt or USB4, where the external link itself is usually the bigger constraint than BAR size.

Troubleshooting: when it won't enable or doesn't seem to help

If the Resizable BAR or Smart Access Memory toggle doesn't appear in BIOS at all, check first that Above 4G Decoding is enabled and saved — on many boards the second option is hidden until the first is turned on and the BIOS is reopened. If it's enabled in BIOS but your driver utility (Intel DSA, AMD Adrenalin, Nvidia's tools) still reports it as off or unsupported, Intel's own troubleshooting documentation notes this can be a cosmetic reporting issue on some AMD-platform combinations, and suggests toggling the BIOS setting off, saving, then back on and saving again. A BIOS update is also worth checking — Resizable BAR support, especially on older 400-series AMD or 10th-Gen Intel boards, was often added well after launch via a firmware update, so a board that "doesn't support it" today might after a firmware flash.

If everything reports enabled and you simply don't notice a difference, that's expected for plenty of games — see the honesty note above. It's a background optimization, not a visible feature toggle like ray tracing or an upscaler; for comparison, that's a very different kind of setting than, say, choosing between AMD FSR and Nvidia DLSS upscaling, where the visual and frame-rate impact is usually obvious immediately.

What to check next on your own system

To confirm where you stand: open your motherboard manufacturer's support page and check for a BIOS changelog mentioning "Resizable BAR," "Re-Size BAR," "Above 4G Decoding," or "Smart Access Memory," and update if an entry exists and you're behind. Then check your GPU vendor's driver release notes for the same terms to make sure your driver is current. Finally, boot into BIOS, confirm UEFI mode, enable Above 4G Decoding, save, reopen, and enable the Resizable BAR/SAM option if it's now present. Verify afterward with Intel DSA, AMD Adrenalin's Performance/Tuning panel, or a third-party GPU diagnostic utility, rather than assuming it's on just because you flipped the switch once.

Written byMara Lindqvist

Mara Lindqvist edits the hardware desk. She covers graphics cards, processors, memory and storage, the foundries and chip designers behind them, and what the numbers on a spec sheet mean for people choosing a PC. Specifications in her stories come from manufacturer spec pages and datasheets.

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