Resizable BAR, often shortened to ReBAR, lets a compatible processor access a graphics card’s full video memory region instead of reading it through smaller windows. In supported games, that can improve performance, although the benefit varies by game, resolution, and hardware. The setting is available on many modern Intel, AMD, and NVIDIA systems, but it must be enabled in the motherboard firmware and supported by the GPU, CPU, and driver.
What goes wrong when the setup is done badly? A careless BIOS change can prevent Windows from booting, especially if the system is installed in Legacy mode rather than UEFI mode. An outdated motherboard BIOS can also cause instability, while forcing unsupported settings may lead to a black screen or make the ReBAR status show as unavailable. The process is usually safe if you record your current settings, update firmware carefully, and change only the options required.
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What You Need
| Item | Why | Optional? |
|---|---|---|
| Compatible desktop PC | You generally need a relatively recent motherboard, CPU, GPU, and UEFI firmware. Check all four components, not just the graphics card. | No |
| Motherboard manual | Menu names differ. One board may call the setting “Above 4G Decoding,” while another places it under PCIe or Advanced settings. | No |
| Current BIOS and GPU driver | ReBAR support is often added or improved through firmware and driver updates. Download the correct files for the exact model. | No |
| Small Phillips screwdriver | Useful if you need to remove the side panel, reseat the graphics card, or check its power cables. | Usually |
| GPU support bracket | A heavy graphics card should remain level and firmly seated. A basic bracket commonly costs about $10–$30. | Yes |
| Alphacool ES D-Plug 31.5mm G1/4 M-M Resizable Fitting Deep Black (17581) | This is a liquid-cooling fitting, priced at about $16.25. It does not enable ReBAR and is relevant only if you already service a compatible custom water-cooling loop. | Yes |
Step-by-Step
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Confirm hardware and operating-system support — 10 to 15 minutes
Identify your motherboard, processor, graphics card, and operating system. ReBAR requires support from the platform as a group. Many newer systems support it, but compatibility is model-specific, particularly on older motherboards and early PCIe generations.
In Windows, press Windows key + R, type msinfo32, and press Enter. Check BIOS Mode. It should say UEFI, not Legacy. If it says Legacy, do not immediately disable Compatibility Support Module (CSM); Windows may fail to boot. Back up important files and research the proper conversion process for your installation first.
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Check your current ReBAR status — 5 minutes
Open the NVIDIA Control Panel, select System Information, and look for Resizable BAR. On supported systems, it should show either Yes or No. AMD users can check the Radeon software information panel; AMD may refer to the related feature as Smart Access Memory.
You can also use a reputable hardware-information utility to confirm whether the PCIe device reports ReBAR as enabled. Record the current status before making changes. If the option is already enabled, no BIOS adjustment is necessary.
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Back up important files and record BIOS settings — 10 minutes
Save work, close applications, and back up documents that would be difficult to replace. A BIOS update or incorrect boot-mode change is uncommon as a cause of data loss, but preparation is sensible.
Photograph or write down custom BIOS settings such as memory profiles, fan curves, boot order, virtualization, and CPU limits. Firmware updates can reset settings to their defaults. If BitLocker or another device-encryption feature is active, have your recovery key available before updating firmware.
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Update the motherboard BIOS if required — 15 to 30 minutes
Visit the motherboard manufacturer’s support page using another device if necessary, and download the BIOS file for the exact board revision. Do not use a file for a similar-looking model. Read the manufacturer’s instructions, place the file on a correctly formatted USB drive if required, and use the board’s built-in update utility.
Connect the computer to reliable power. Do not turn it off, press the reset button, or remove the USB drive while the update is running. The system may restart several times. If the board already has a BIOS version that supports ReBAR, updating may not be necessary.
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Enter the UEFI firmware menu — 2 to 5 minutes
Restart the computer and repeatedly press the firmware key during startup. Common choices are Delete, F2, or, on some systems, F10 or F12. Windows also provides an advanced-startup route: open Settings, choose Recovery, select Advanced startup, then use the UEFI firmware option.
Firmware interfaces vary by brand. If you cannot find an option, switch from a simplified view to advanced mode, often by pressing F7.
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Enable Above 4G Decoding — 2 to 5 minutes
Find Above 4G Decoding. It may be under Advanced, PCIe, PCI Subsystem Settings, Chipset, or a similar menu. Set it to Enabled. This allows the system to map large PCIe memory ranges and is normally required before ReBAR can work.
Do not confuse it with unrelated settings such as “4G Memory” or an integrated-graphics memory allocation option. Use your manual if the wording differs.
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Disable CSM and enable ReBAR — 2 to 5 minutes
Find Compatibility Support Module, or CSM, and set it to Disabled. ReBAR generally requires a pure UEFI boot configuration. Next, locate Resizable BAR, Re-Size BAR Support, or a similar PCIe option and set it to Enabled or Auto.
Some AMD boards show a single Smart Access Memory setting; others still expose Above 4G Decoding and ReBAR separately. Leave PCIe link speed on Auto unless your motherboard manual specifically recommends another setting.
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Save changes and boot into Windows — 3 to 10 minutes
Choose Save Changes and Exit. The computer may take longer than usual to start while the firmware retrains memory or rebuilds its hardware configuration. If Windows loads normally, open your GPU control panel and verify that ReBAR now reports as enabled.
If the computer repeatedly returns to the BIOS, restore the previous CSM or boot settings. If it does not display an image, turn the system off, disconnect power, and consult the motherboard’s clear-CMOS instructions. Avoid randomly changing several settings at once.
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Install or update the graphics driver and test normally — 10 to 20 minutes
Install the current driver designed for your exact GPU. Restart afterward and confirm the ReBAR status again. Test a familiar game for stability rather than assuming every title will improve. ReBAR is not a guaranteed frame-rate upgrade, and some games may show no measurable change.
Keep temperatures, crashes, and visual glitches in mind during normal use. Do not increase GPU voltage, power limits, or overclock settings simply because ReBAR is enabled.
Mistakes to Avoid
- Disabling CSM before confirming UEFI: A Legacy installation may stop booting. Check BIOS Mode first and back up your data.
- Updating the wrong BIOS: Match the exact motherboard model and revision. A failed firmware flash can require manufacturer service.
- Assuming every GPU supports ReBAR: Some older cards lack support, while others need a specific VBIOS.
- Skipping the driver check: Firmware alone cannot guarantee that the operating system and GPU driver will activate the feature.
- Changing unrelated performance settings: Leave CPU overclocking, memory timings, and PCIe generation settings alone during troubleshooting.
- Removing a water-cooling fitting for this task: The Alphacool fitting listed above has no relationship to ReBAR. Never open a liquid-cooling loop while the computer is powered.
How Often
Resizable BAR is normally a one-time configuration. You do not need to enable it for each game or repeat the process on a schedule. Recheck the status after a motherboard BIOS update, GPU VBIOS update, major hardware replacement, or a full BIOS reset. A driver update alone usually does not require changing the firmware settings again.
When to Call a Pro or Replace
Get professional help if the computer will not display an image after a BIOS change, repeatedly enters a boot loop, cannot detect the graphics card, or reports firmware errors. A technician can clear CMOS, recover the BIOS, inspect the PCIe slot, and verify UEFI boot files without risking unnecessary part replacement.
Consider replacing hardware only when the component is genuinely unsupported, defective, or too old to receive a compatible BIOS or VBIOS. If a current GPU works normally but ReBAR is unavailable, replacing the motherboard may cost roughly $100–$400 and is often less sensible than leaving the feature disabled. ReBAR is an enhancement, not a requirement for a functioning gaming PC.
FAQ
Does enabling Resizable BAR improve gaming performance?
It can, but the result depends on the game, GPU, CPU, resolution, and driver. Some titles show a small improvement, some show no meaningful difference, and a few may require a driver profile that limits or disables the feature.
Can I enable ReBAR without updating my BIOS?
Yes, if your existing BIOS already supports it. Check the firmware release notes and look for the ReBAR setting before updating. If the setting is missing, a compatible BIOS update may be required.
What if Windows will not boot after disabling CSM?
Return to the BIOS and re-enable CSM so the system can start, then restore your previous configuration. Your Windows installation may be using Legacy boot files or an MBR disk. Converting the installation to UEFI/GPT should be done only after a backup and with instructions specific to your operating system.
Is ReBAR the same as AMD Smart Access Memory?
They are closely related technologies. AMD markets its supported implementation as Smart Access Memory, while the general PCIe feature is called Resizable BAR. The required settings and exact menu names depend on your AMD platform.
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