You enable Resizable BAR by turning off Legacy/CSM boot, turning on Above 4G Decoding and Re-Size BAR Support in the system BIOS, and then confirming the feature is active in your GPU control panel.
Resizable BAR lets your CPU access the full memory buffer on your graphics card at once, rather than in small 256MB chunks. In supported games, this can deliver a noticeable frame-rate lift. The catch is that making it work requires matching support in four places: your motherboard BIOS, your GPU’s firmware (VBIOS), your display driver, and your Windows boot mode. This guide walks you through each layer, from the BIOS key you need to press at startup to confirming the feature is actually running.
Prerequisites: Do You Have Support?
Before diving into the BIOS, run a quick hardware check. You need all four of these:
- A compatible motherboard with a BIOS update that includes the sizing options (most Intel 400-series and newer, plus AMD 500-series and newer motherboards support it).
- A compatible GPU. On the Nvidia side, that means a GeForce RTX 30 Series card or newer—Nvidia’s official support article names the RTX 30 Series specifically as the starting generation.
- A display driver that supports Resizable BAR. Nvidia’s first game-ready driver to enable the feature was version 465.89 WHQL (released March 30, 2021). You should be on the latest driver anyway, but this is a good floor to keep in mind.
- Windows installed in UEFI mode with Legacy/CSM boot disabled.
If your system meets all four criteria but the BIOS options are missing, check your motherboard manufacturer’s support page for a firmware update. Many boards shipped with early BIOS versions that didn’t include the sizing menus.
Step 1: Disable CSM and Enable UEFI Boot
Resizable BAR cannot work if your system is using Compatibility Support Module (CSM) or Legacy boot mode. The PCI address mapping that the feature depends on is only available in native UEFI mode. This is the most common single mistake users make—they toggle the Resizable BAR setting in BIOS but leave CSM enabled, and nothing happens.
To fix this, enter your motherboard BIOS and look for a setting called CSM Support, Launch CSM, or Legacy Mode. Set it to Disabled. Then confirm that your boot mode is set to UEFI rather than Legacy or “UEFI with CSM.” On Gigabyte boards, this step is clearly documented: CSM Support must be set to Disabled under the Settings tab in Advanced Mode. On ASUS boards, the same rule applies—ASUS explicitly says “Launch CSM must be Disabled” for Resizable BAR to work.
If you disable CSM and your system won’t boot, it means Windows was originally installed in Legacy mode. You can convert the boot drive from MBR to GPT using Microsoft’s MBR2GPT tool without a reinstall, or do a clean install of Windows in UEFI mode. Either approach works, but the clean install is simpler for most people.
Step 2: Enable Above 4G Decoding and Re-Size BAR Support
With UEFI boot active, the next step is to enable the two specific BIOS settings that control Resizable BAR. The exact menu names vary by motherboard vendor, which is a common point of confusion. You are looking for two settings in the same area of your BIOS, usually under the PCI Subsystem Settings or Peripherals or an equivalent submenu.
What To Look For In Your BIOS
Enable the first option, usually labeled Above 4G Decoding or Above 4G MMIO. This setting re-maps PCIe resources above the 4GB address boundary, which makes room for the full GPU frame buffer to be addressable by the CPU.
Then enable the second option. Its label depends on who made your motherboard. Intel’s own guidance says it can appear as Re-Size BAR Support, Resizable BAR, Resize BAR, Smart Access Memory, or Clever Access Memory. Set this to Enabled or Auto—whichever your board offers.
Here’s how the full step looks on a few major brands based on their official documentation:
| Brand | BIOS Entry Key | Key Setting Order |
|---|---|---|
| ASUS | Delete at startup | Click the Resize BAR icon → Set to On → Press F10 and OK to reboot |
| Gigabyte | Delete at startup (Del) | Advanced Mode → Settings → Above 4G Decoding = Enabled → Re-Size BAR Support = Auto → CSM Support = Disabled → Save & Exit |
| MSI | Delete at startup | Settings → Advanced → PCI Subsystem Settings → Re-Size BAR Support = Enabled |
| ASRock | F2 or Delete | Advanced → PCI Configuration → Above 4G Decoding = Enabled → Resizable BAR = Enabled |
| Intel (generic) | F2 or Del | Disable CSM → Enable UEFI → Enable Above 4G Decoding → Enable Re-Size BAR Support |
| AMD AM5 (reference) | Del at startup | Advanced → PCI Subsystem Settings → Above 4G Decoding = Enabled → Re-Size BAR Support = Enabled |
| Lenovo (desktop prebuilt) | F1 at startup | Devices → PCI → Resizable BAR = Enabled |
After changing these settings, save your changes and reboot. The machine will restart—this is where you want to confirm the feature is working in the OS.
How To Confirm Resizable BAR Is Enabled
A BIOS setting alone doesn’t guarantee success. The feature must also be supported by the GPU firmware (VBIOS) and the display driver. Confirmation is quick in the GPU control panel or a utility like GPU-Z.
On Nvidia cards, open the Nvidia Control Panel, go to Help and then System Information. Look for the line that reads Resizable BAR. If it says Yes, you are good to go. This is the method Nvidia’s own support article recommends, and it is also the confirmation path described by Gigabyte for its own systems. If it says No, go back to the BIOS, re-check that CSM is disabled, and make sure you are on the latest graphics driver. Then reboot again.
On Intel Arc GPUs, open the Intel Driver and Support Assistant (Intel DSA) and check the status of Resizable BAR from the application’s main dashboard. Intel’s own documentation confirms this as the verification step for its ARC graphics.
For AMD Radeon cards, the feature is called Smart Access Memory. Open the AMD Software: Adrenalin Edition, click on Performance and then Tuning, and look for the Smart Access Memory toggle. If it shows as Enabled, Resizable BAR is active.
| GPU Brand | Verification Tool | Where To Look |
|---|---|---|
| Nvidia GeForce | Nvidia Control Panel | Help → System Information → “Resizable BAR: Yes” |
| Intel Arc | Intel DSA | Main dashboard status indicator |
| AMD Radeon | AMD Software: Adrenalin Edition | Performance → Tuning → “Smart Access Memory: Enabled” |
| Any GPU | GPU-Z (TechPowerUp) | Look for Resizable BAR box on the main tab |
Is There a Performance Gain Worth The Effort?
The performance benefit of Resizable BAR is real but varies by title. Nvidia’s own benchmarks for its RTX 30 series showed improvements ranging from negligible in some games to as high as 10–15 percent in titles like Assassin’s Creed Valhalla, Battlefield V, and Watch Dogs: Legion. The feature reduces CPU overhead by allowing direct memory access to the entire GPU buffer, which is most beneficial in CPU-limited scenarios at 1080p and 1440p.
Intel’s ARC GPUs benefit more consistently because Resizable BAR is fundamental to the architecture—Intel explicitly requires it for optimal performance on its dedicated graphics cards. For Nvidia and AMD cards, the gains are more situational. There is no downside to having it enabled if your system supports it, so the setup effort is worth the potential free performance in several popular titles.
Common Problems and How To Fix Them
A few issues come up repeatedly. Here are the fixes for the most common situations.
- The BIOS options are invisible. Update your motherboard BIOS to the latest version. Many early firmware releases didn’t expose Re-Size BAR menus, even though the chipset supported it.
- You enabled Re-Size BAR but the Nvidia Control Panel says No. The most likely cause is that CSM is still enabled. Go back into the BIOS and disable CSM or Legacy boot. If CSM is already off, update your GPU VBIOS. Gigabyte advises that “the VBIOS of each model is not universal and incompatible with other models,” so download the correct package from your GPU manufacturer’s support page.
- Your system won’t boot after disabling CSM. Windows was installed in Legacy mode. You need to convert the boot drive from MBR to GPT. Microsoft’s MBR2GPT tool can do this from inside Windows without data loss, or you can reinstall in UEFI mode.
- You have an AMD processor and an Nvidia GPU but the setting is labeled Smart Access Memory. AMD boards often use the Smart Access Memory label even with Nvidia cards. Enable it anyway—both Smart Access Memory and Re-Size BAR are the same PCIe specification under different marketing names.
References & Sources
- ASUS. “What Is Resizable BAR and How To Enable It.” ASUS’s official FAQ covering the BIOS steps for enabling Resizable BAR.
- Gigabyte. “NVIDIA Resizable BAR.” Gigabyte’s official product support page on enabling and verifying Resizable BAR.
- Intel. “Enable Resizable BAR on Intel Arc Graphics.” Intel’s support document on Resizable BAR requirements and steps for its graphics products.
- Nvidia. “NVIDIA Resizable BAR Comes to GeForce RTX 30 Series Desktops.” Nvidia’s official announcement and guidance on Resizable BAR for GeForce RTX 30 series GPUs.