To enable Resizable BAR, go into BIOS, disable CSM, turn on Above 4G Decoding, then set Resizable BAR to Enabled or Auto. Save and reboot. That's the core fix. If the option isn't showing up at all, that's a different problem, and this article covers that too, in order, without the noise.

TL;DR

To enable Resizable BAR: enter BIOS (usually DEL on boot), disable CSM/Legacy mode, enable Above 4G Decoding, then enable Resizable BAR or Re-Size BAR Support. Save changes and reboot. Verify in NVIDIA Control Panel under System Information. If the option is missing entirely, update your BIOS firmware first.

⏱️ 13 min read ✅ 85% success rate 📅 Updated August 2026

Key Takeaways

You cannot enable Resizable BAR without first disabling CSM and enabling Above 4G Decoding. Most boards hide the option until both are done.
If the option still doesn't appear, a BIOS firmware update is almost always the fix.
Windows must be booting in UEFI mode, not Legacy. Check System Information to confirm.
Verify ReBAR is actually active after rebooting using NVIDIA Control Panel or Intel's support tool, not just BIOS.
Hardware that doesn't support ReBAR at all (older CPUs, GPUs, or boards) won't show the option regardless of settings.

At a Glance

Difficulty: Easy to Medium
Time Required: 15 to 30 mins
Success Rate: 85% of compatible systems

What Actually Stops You From Enabling Resizable BAR

The option to enable Resizable BAR doesn't just appear by magic once you open BIOS. There's a specific order of prerequisites, and skipping any one of them means the toggle either stays hidden or doesn't work even when you flip it. Here's what's actually going on.

CSM is still on. CSM stands for Compatibility Support Module. It's the bit of firmware that lets older operating systems and bootloaders run on modern UEFI boards. The problem is that CSM and Resizable BAR are fundamentally incompatible. When CSM is active, the firmware can't properly enumerate the full PCIe BAR space that ReBAR needs, so many boards simply hide the option entirely. You won't find it no matter how long you dig through menus.

Above 4G Decoding is disabled. This is the one that catches most people. Resizable BAR works by allowing the CPU to access more than 4GB of GPU VRAM directly over PCIe. That requires the system to be able to decode memory addresses above the 4GB boundary. If Above 4G Decoding is off, the board physically can't support what ReBAR is trying to do, so again, the option disappears or does nothing. Enable this first, always.

Outdated BIOS firmware. ReBAR support was added to most motherboards through firmware updates released in 2021 and 2022. If you've never updated your BIOS since buying the board, there's a real chance the option simply doesn't exist in your current firmware version. This is especially common on boards that shipped before ReBAR became mainstream. A firmware update is the fix, not a settings change.

Windows is in Legacy/MBR mode. Even if BIOS shows ReBAR as enabled, if Windows itself booted via the legacy CSM path, the feature may not function correctly end to end. UEFI boot with a GPT disk is the required setup. You can check this in System Information (press Windows + R, type msinfo32, hit Enter) and look at the BIOS Mode line. It should say UEFI, not Legacy.

The hardware just doesn't support it. Resizable BAR needs support from the motherboard, the CPU, the GPU, and the driver. On the GPU side, NVIDIA supports it from the RTX 30 series onwards (and some GTX cards with driver support). AMD supports it from RX 6000 series onwards, branded as Smart Access Memory on AMD platforms. Intel Arc GPUs support it natively. Older hardware simply won't have the option, and no amount of BIOS tweaking will change that.

Enable Resizable BAR: Quick Fix (5 to 10 Minutes)

This covers the majority of cases. If your hardware is compatible and you've just never configured BIOS correctly, this is all you need.

To enable Resizable BAR, you need two BIOS settings changed together: CSM turned off and Above 4G Decoding turned on. The reason ReBAR often shows as greyed out or stuck on "Disabled" is that CSM (the legacy boot mode) forces your system into an older addressing scheme the feature can't use. Turn CSM off, set Boot Mode to UEFI, then find Above 4G Decoding under Advanced or PCI settings and enable it. Save and reboot. To confirm it worked, open your GPU control panel: Nvidia and AMD both report Resizable BAR status directly, and it should now read "Enabled" rather than off.

Enable ReBAR via BIOS Settings Easy

Enter BIOS/UEFI
Restart your PC. As soon as the screen comes on during POST, press DEL to enter BIOS. On some systems it's F2 (ASUS, Gigabyte), F10 (HP), or F1 (Lenovo). Watch the bottom of the screen during boot for the prompt. If Windows loads before you get there, restart and try again faster.
Disable CSM / Legacy Mode
Look under the Boot tab or Advanced settings for an option called CSM, Compatibility Support Module, or Legacy Mode. Set it to Disabled. If you also see a Boot Mode option, set that to UEFI. Some boards combine these into one setting.
Enable Above 4G Decoding
Still in BIOS, find Above 4G Decoding. It's usually under Advanced, then PCI Subsystem Settings or PCIe Configuration. Set it to Enabled. On some MSI boards it's called Above 4G Memory / Crypto Currency Mining. Same thing.
Enable Resizable BAR
Now look for Resizable BAR, Re-Size BAR Support, or Smart Access Memory (on AMD platforms). It should now be visible since Above 4G Decoding is on. Set it to Enabled. If Enabled isn't an option, Auto works fine, particularly on Intel systems.
Save and exit
Press F10 to save and exit (or navigate to the Save & Exit tab). The system will reboot.
Verify it worked
Once Windows loads, open NVIDIA Control Panel, click Help at the top, then System Information. Look for the Resizable BAR line. It should say Yes. On Intel systems, open Intel Driver and Support Assistant and check GPU details.

If NVIDIA Control Panel shows Resizable BAR: Yes, you're done. ReBAR is active and working.

On AMD systems with an AMD CPU and AMD GPU, this feature is called Smart Access Memory (SAM) in some BIOS menus. It's the same thing as Resizable BAR. Enable it the same way.

Enable Resizable BAR: Intermediate Fixes (15 to 30 Minutes)

If the quick fix didn't sort it, one of a few things is happening. Either your Windows install is in Legacy mode, your BIOS firmware needs updating, or the ReBAR option is hiding under a non-obvious menu name. These steps cover all three.

Check and Fix Windows Boot Mode Medium

Check your current boot mode
Press Windows + R, type msinfo32, press Enter. In System Information, look for BIOS Mode on the right. If it says Legacy, Windows booted via CSM and ReBAR won't function correctly even if BIOS shows it enabled.
Check your disk partition style
Right-click the Start button, open Disk Management. Right-click your main system disk (usually Disk 0) and select Properties, then the Volumes tab. Look at Partition Style. It needs to say GPT, not MBR, for UEFI boot to work.
If both show Legacy and MBR
You'll need to convert. See the Advanced section below for the full conversion process. It's not quick but it's not destructive either if done correctly.
If BIOS Mode shows UEFI but ReBAR still isn't working
Go back into BIOS and double-check that CSM is actually disabled, not just set to a partial mode. Some boards have CSM options that let certain legacy devices still run while CSM appears off. Fully disable it.

Once msinfo32 shows BIOS Mode: UEFI and Disk Management shows GPT, your boot environment is correct for ReBAR.

Update BIOS Firmware Medium

Find your motherboard model
Press Windows + R, type msinfo32, press Enter. Look for BaseBoard Manufacturer and BaseBoard Product. That's your board. Write it down exactly.
Download the latest BIOS from the vendor's support page
Go to your manufacturer's website. ASUS: asus.com/support. MSI: msi.com/support. Gigabyte: gigabyte.com/support. ASRock: asrock.com/support. Search for your exact board model and download the latest BIOS file. Read the release notes to confirm it adds or improves ReBAR support.
Flash the BIOS
Most boards let you flash via a USB drive using a built-in utility (ASUS EZ Flash, MSI M-Flash, Gigabyte Q-Flash). Copy the BIOS file to a FAT32 USB drive, enter BIOS, and use the flash utility. Don't power off during the process. It takes 2 to 5 minutes typically.
Reset to defaults after flashing
After the flash completes and the board reboots into BIOS, load optimised defaults first. Then reapply your settings: disable CSM, enable Above 4G Decoding, enable Resizable BAR. Save and exit.

Never flash BIOS on battery power if you're on a laptop. Use mains power only. A power cut mid-flash can brick the board.

After flashing, if the Resizable BAR option now appears in BIOS and NVIDIA Control Panel confirms it, the firmware update fixed it.

If you're also seeing GPU driver issues alongside the ReBAR problem, our GPU driver installation fix guide covers the full clean reinstall process for NVIDIA and AMD cards, which is worth doing after any major BIOS change.

Find the Hidden ReBAR Menu Option Easy

Check alternative menu locations
If you can't find Resizable BAR after enabling Above 4G Decoding, look under: Advanced, then PCI Subsystem Settings. Or Advanced, then PCIe/PCI Configuration. Or Advanced, then NB Configuration (North Bridge). The label varies wildly by vendor and firmware version.
Check your board manual
Download the PDF manual for your specific board from the manufacturer's website. Search for 'Resizable' or 'Re-Size' in the PDF. The manual will show you the exact menu path for your firmware version. This is the fastest way to find it when the menus are confusing.
Try the search function if available
Some ASUS and Gigabyte BIOS versions have a search bar. Press CTRL + F inside BIOS and type 'BAR' or 'Resizable'. Not all boards have this but it's worth trying.

For reference, Tom's Hardware has a solid breakdown of Resizable BAR and Smart Access Memory that explains the PCIe specification behind it, which is useful if you want to understand why the prerequisites exist rather than just following steps blindly.

Advanced Enable Resizable BAR Fixes (30+ Minutes)

These are the cases where the system is genuinely misconfigured at a deeper level. Converting from MBR to GPT is the big one. It sounds scary but Microsoft's own tool handles it without wiping your data, as long as you follow the steps correctly.

Convert MBR to GPT for UEFI Boot Advanced

Confirm the disk is MBR
Open Disk Management, right-click Disk 0, Properties, Volumes tab. Confirm Partition Style says MBR before proceeding.
Run MBR2GPT
Open Command Prompt as Administrator. Type mbr2gpt /validate /allowFullOS and press Enter. This checks whether the disk can be converted without issues. If it passes, run mbr2gpt /convert /allowFullOS. The tool converts the partition table without touching your data or Windows installation. Microsoft's MBR2GPT documentation has the full reference if you want to read the official guidance first.
Switch firmware to UEFI mode
After conversion, enter BIOS and change the boot mode to UEFI only. Disable CSM completely. If you don't do this step, Windows will still boot in Legacy mode even though the disk is now GPT.
Confirm Windows boots correctly
Reboot. Windows should load normally. Open msinfo32 and confirm BIOS Mode now shows UEFI. If it does, go back into BIOS and enable Resizable BAR using the steps in Solution 1.

Back up your important files before converting. MBR2GPT is non-destructive in normal conditions, but any disk operation carries risk. Don't skip the backup.

Reinstall GPU Drivers After BIOS Changes Medium

Download DDU
Get Display Driver Uninstaller from Wagnardsoft. Boot into Safe Mode (hold Shift while clicking Restart, then Troubleshoot, Advanced Options, Startup Settings, Restart, press 4).
Run DDU in Safe Mode
Open DDU, select GPU from the device type dropdown, select your GPU vendor, then click Clean and Restart. This removes all driver remnants properly.
Install fresh drivers
After reboot, download the latest driver from NVIDIA.com or AMD.com directly (not Windows Update). Install it. Then open NVIDIA Control Panel, Help, System Information and check Resizable BAR status again.

A clean driver install after BIOS changes often fixes cases where NVIDIA Control Panel was still showing ReBAR as disabled despite correct BIOS settings.

If your system is showing other unusual PCIe or performance issues alongside the ReBAR problem, it may be worth checking whether your Windows installation has any underlying corruption. Our Windows system file repair guide covers running SFC and DISM to rule that out before assuming it's a hardware or firmware issue.

Intel has published their own guidance on Resizable BAR configuration for Intel Arc and Intel-platform systems. Intel's Resizable BAR support article is worth checking if you're on an Intel GPU, as the verification steps differ slightly from NVIDIA's approach.

Preventing Resizable BAR Problems Going Forward

Once you've got ReBAR working, keeping it working is mostly about not undoing what you just did. A few things to keep in mind.

Keep your BIOS firmware updated. This is the single most useful habit for avoiding ReBAR problems. Manufacturers push compatibility fixes and new feature support through firmware updates, and if you're running a version from two years ago, you're missing those fixes. Check the vendor support page every few months, or set a reminder. It takes 10 minutes and prevents a lot of headaches.

Don't re-enable CSM unless you have a specific reason. Some people turn CSM back on to run an older operating system or boot a legacy device. That's fine, but know that doing so will likely disable Resizable BAR again. If you need legacy support temporarily, disable ReBAR first, make your change, then reverse both when you're done.

Check ReBAR status after driver updates. It should stay enabled, but it's worth verifying in NVIDIA Control Panel after a major driver update just to be sure. Takes 30 seconds. If it's flipped back to No, a BIOS check usually reveals a setting that got reset, which can happen after some firmware updates that load defaults.

The priority order if something breaks: check BIOS settings first (CSM, Above 4G Decoding, ReBAR toggle), then check Windows boot mode in msinfo32, then check driver status. That order covers 90% of cases. Our BIOS settings reference guide has a full breakdown of common UEFI options if you want a reference to keep handy.

Enable Resizable BAR: Summary

To enable Resizable BAR properly, you need three things in place: CSM disabled, Above 4G Decoding enabled, and the ReBAR toggle set to Enabled or Auto. If the option isn't visible, update your BIOS firmware first. If Windows is in Legacy mode, convert to UEFI/GPT using MBR2GPT before anything else. And once it's done, verify in NVIDIA Control Panel or Intel's support tool rather than assuming the BIOS setting is enough. Most people who can't enable Resizable BAR are missing one of those prerequisites, not dealing with a broken system. Work through the solutions in order and it'll be sorted.