Resizable BAR, often shown as ReBAR or Smart Access Memory, lets your CPU access the graphics card’s entire memory pool at once instead of in small chunks. In supported games it can add a few percent of free performance, and occasionally more. The catch is that it is often disabled by default, and turning it on requires the right settings in your motherboard BIOS. Here is how to enable it safely.
What Resizable BAR Actually Does
Traditionally the CPU could only see graphics memory in 256MB windows. Resizable BAR removes that limit so the CPU can address all of the GPU’s VRAM directly, which streamlines certain data transfers. The result is usually a small frame-rate gain in supported titles, though a handful of games see little change or, rarely, a slight regression. It is generally worth enabling.
What you need first
Three conditions must be met: a supported CPU and motherboard, a graphics card that supports the feature, and an updated BIOS and GPU driver. Older platforms may need a BIOS update to expose the option at all.
Step-by-Step: Enabling ReBAR
| Step | Action | Notes |
|---|---|---|
| 1 | Update BIOS and GPU drivers | Enables and stabilizes the feature |
| 2 | Enter BIOS at boot | Usually Delete or F2 |
| 3 | Enable UEFI-only boot / disable CSM | ReBAR requires pure UEFI mode |
| 4 | Find Above 4G Decoding, enable it | Prerequisite setting |
| 5 | Enable Resizable BAR / SAM | Often near Above 4G Decoding |
| 6 | Save and exit | System reboots |
The exact menu names vary by brand, but the pattern is consistent: enable Above 4G Decoding first, then the Resizable BAR toggle, with the system already booting in UEFI mode.
Verifying It Worked
Check the driver control panel
After rebooting into Windows, your GPU’s control panel or system information tool will report Resizable BAR as enabled. If it still shows disabled, the most common causes are CSM still turned on or Above 4G Decoding not enabled.
The CSM gotcha
If enabling UEFI-only mode makes your PC fail to boot, your Windows install may be in legacy mode. In that case leave CSM as it was and research converting the disk to GPT before retrying, rather than forcing the change blindly.
Troubleshooting When ReBAR Won’t Turn On
If the option is missing or refuses to stick, work through the usual causes. First, confirm your BIOS is current, since older firmware may not expose the feature at all on some boards. Second, make sure the system is booting in pure UEFI mode with CSM disabled, because Resizable BAR depends on it. Third, verify Above 4G Decoding is enabled, as the ReBAR toggle is often unavailable until it is. If all three are set and the GPU control panel still reports it disabled, update the graphics driver, since the feature is enabled jointly by firmware and driver.
Per-game behavior
Once enabled system-wide, some drivers apply Resizable BAR selectively, turning it on for games known to benefit and leaving it off elsewhere. That is normal and usually optimal. You do not need to force it on for every title; the driver’s profile approach avoids the rare cases where the feature hurts. If you are chasing benchmarks, you can test specific games with it on and off, but for everyday use the default behavior is fine.
Is it worth the effort?
For a few minutes of BIOS work, enabling ReBAR is a reasonable free tune-up. Do not expect dramatic gains; think of it as reclaiming a small, consistent slice of performance in supported titles rather than a game-changer. It is most worth doing on a fresh build when you are already in the BIOS setting up memory profiles and boot options.
FAQ
Will Resizable BAR always improve performance?
No. Gains depend heavily on the specific game. Many titles see a small boost, some see nothing, and a few can dip slightly. On balance it is worth enabling, and you can always turn it off if you notice a problem in a particular game.
Is it safe to enable ReBAR?
Yes, on supported hardware with updated firmware and drivers it is a standard, supported feature. The only real risk is the CSM change exposing a legacy Windows install, which is a boot-mode issue rather than damage to hardware.
Bottom Line
Enabling Resizable BAR is a quick, free way to claw back a little gaming performance. Update your BIOS and drivers, switch to UEFI-only boot, turn on Above 4G Decoding, then flip the ReBAR toggle and verify it in your GPU control panel. Just watch the CSM setting so you do not strand a legacy Windows install.
