If you have a modern GPU and a compatible motherboard but haven’t enabled Resizable BAR, you’re leaving free performance on the table. This guide explains exactly what ReBAR is, which hardware supports it, and how to turn it on.
What Is Resizable BAR?
Resizable BAR (Base Address Register) is a PCI Express feature that allows the CPU to access the entire GPU framebuffer at once, rather than in small 256 MB chunks. Under the old default behavior, your CPU had to transfer data to the GPU in multiple small transactions, creating a bottleneck during asset streaming and draw calls.
With ReBAR enabled, the CPU can read and write to all of the GPU’s VRAM simultaneously. NVIDIA markets this feature as Smart Access Memory (SAM) when used on AMD platforms, and AMD calls it Smart Access Memory period. Intel calls its implementation Resizable BAR as well on Arc GPUs. The underlying PCIe spec is the same regardless of branding.
Performance Impact
Gains vary significantly by game and GPU:
| Game | Performance Gain (avg) |
|---|---|
| Cyberpunk 2077 | 3–8% |
| Battlefield 2042 | 5–12% |
| Forza Horizon 5 | 4–9% |
| Spider-Man Remastered | 2–6% |
| Red Dead Redemption 2 | 1–4% |
Some titles see no gain, and a small number of older games can actually regress slightly. The safest move is to enable it and test your specific workload.
Hardware Requirements
Before diving into BIOS settings, confirm your system qualifies:
- GPU: NVIDIA RTX 2000 series or newer, AMD RX 5000 series or newer, Intel Arc
- CPU: Intel 10th gen (Comet Lake) or newer; AMD Ryzen 3000 series (Zen 2) or newer
- Motherboard: Must support Above 4G Decoding and Resizable BAR in UEFI (most boards from 2020 onward do after a BIOS update)
Note: Even if your motherboard lists ReBAR support, it sometimes requires a BIOS update to a version that actually enables the option. Check your board manufacturer’s website.
Step 1 — Update Your BIOS
This is the most commonly skipped step. Manufacturers added ReBAR support in later BIOS revisions, so an older BIOS may not have the option at all.
- Visit your motherboard manufacturer’s support page (ASUS, MSI, Gigabyte, ASRock, etc.)
- Find the latest BIOS for your exact board model
- Flash it using the built-in BIOS update utility (e.g., ASUS EZ Flash, MSI M-Flash, Gigabyte @BIOS)
Never flash your BIOS from a battery-powered laptop or during a storm. Interrupted flashes can brick the board.
Step 2 — Enable Above 4G Decoding
ReBAR requires Above 4G Decoding to be active first. Without it, ReBAR won’t appear or won’t work correctly.
- Reboot and enter UEFI (typically Delete or F2 during POST)
- Find Above 4G Decoding — usually under Advanced > PCI Subsystem Settings or similar
- Set it to Enabled
On some boards this setting is labeled Above 4GB MMIO BIOS Assignment.
Step 3 — Enable Resizable BAR
With Above 4G Decoding on, find the ReBAR option:
- ASUS: Advanced > System Agent Configuration > Above 4G Decoding → then Re-Size BAR Support in PCIe settings
- MSI: Settings > Advanced > PCI Subsystem Settings > Re-Size BAR Support
- Gigabyte: Settings > IO Ports > Above 4G Decoding, then Re-Size BAR Support below
- ASRock: Advanced > Chipset Configuration > Above 4G Decoding → Resizable BAR Support
Set Resizable BAR Support to Auto or Enabled, then save and exit (F10 on most boards).
Step 4 — Verify in Windows 11
After booting into Windows 11, confirm ReBAR is active:
Using GPU-Z
- Download and open GPU-Z (free from TechPowerUp)
- On the main card tab, look for the Resizable BAR field
- It should show Yes
Using NVIDIA Control Panel (NVIDIA GPUs)
- Open NVIDIA Control Panel
- Go to Help > System Information
- Under the Components section, look for Resizable BAR — it will say Yes if active
Using AMD Software: Adrenalin Edition (AMD GPUs)
- Open AMD Software: Adrenalin Edition
- Navigate to Performance > Tuning
- Look for AMD Smart Access Memory — it should show as Enabled
Troubleshooting
Option not visible in BIOS: Update your BIOS. If it’s already current and the option is still missing, your board may not support it despite claims to the contrary — check the manufacturer’s compatibility list.
ReBAR shows enabled but GPU-Z shows No: Some boards require you to also enable SR-IOV or 4G Decode in a secondary menu. Dig through your BIOS Advanced settings carefully.
System won’t POST after enabling: Reset CMOS (remove the battery or use the CLR_CMOS jumper on your board) to restore defaults, then re-enable one setting at a time.
Game crashes after enabling: A handful of older titles have shader compilation issues with ReBAR active. Disable it for those specific games or roll back the GPU driver to a known-stable version.
Conclusion
Resizable BAR is one of the easiest free performance wins available on modern hardware. The BIOS process takes about five minutes, and games that benefit from it see real, measurable gains without touching anything else. If your hardware supports it, there’s no reason not to have it enabled.