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Enable Resizable BAR in the BIOS and Confirm It Is Active

Re-Size BAR lets the CPU address the whole GPU memory buffer at once. Enable Above 4G Decoding, boot in UEFI mode and verify the result in GPU-Z.

by@guidox updated:10/30/26 time:20 min level:Advanced tested on:Windows 11 24H2, GeForce driver 560 works on:Windows 10, Windows 11, UEFI boot, BIOS 2021+ tools:GPU-Z
⚠ Safety notice

BIOS changes can leave the board unbootable until CMOS is cleared. Have the clear-CMOS jumper or battery location at hand before you save.

TL;DR

Turn on **Above 4G Decoding** and **Re-Size BAR Support**, boot in **UEFI mode** with CSM off, then check **Resizable BAR: Yes** in GPU-Z. Most games gain 3 to 8%, some gain nothing.

Before you start

Requirements

  • GPU with ReBAR support (RTX 30 series and newer, RX 6000 and newer, Intel Arc)
  • Motherboard BIOS from 2021 or newer
  • GPU-Z from https://www.techpowerup.com/gpuz/
  • A GPT system disk - a legacy MBR install cannot boot in UEFI mode
Step by step

Instructions

01

Read the current state

Open GPU-Z, switch to the **Advanced** tab and select **PCI Express** in the dropdown. The **Resizable BAR** row tells you whether it is disabled right now.

GPU-Z > Advanced > PCI Express > Resizable BAR
02

Check that the system disk is GPT

Run the disk query in an admin PowerShell. **PartitionStyle** must say GPT, otherwise the board only boots with CSM enabled and ReBAR stays off.

Get-Disk | Select-Object Number, FriendlyName, PartitionStyle
⚠ warningConverting MBR to GPT needs a backup first. Do not attempt it as part of this guide.
03

Disable CSM in the UEFI

Reboot into the firmware with Del or F2, open the **Boot** page and set **CSM Support** to Disabled. The boot mode then switches to UEFI Only.

Boot > CSM Support > Disabled
Boot Mode > UEFI Only
04

Enable both PCI options

On the **Advanced > PCI Subsystem Settings** page set **Above 4G Decoding** to Enabled, save, re-enter the firmware, then set **Re-Size BAR Support** to Enabled. Some boards hide the second option until the first is saved.

Above 4G Decoding > Enabled
Re-Size BAR Support > Enabled
⚠ warningOn older boards Above 4G alone can stop the GPU from initialising. Know where the clear-CMOS jumper is before you save.
05

Boot into Windows and verify

GPU-Z should now show **Resizable BAR: Yes** on the PCI Express page. Task Manager > Performance > GPU also shows the BAR size instead of 256 MB.

tipA GPU-Z entry for BAR1 larger than 256 MB confirms the firmware side worked.
06

Measure the gain per game

Run the game's own benchmark twice: once with ReBAR on, once off, at the resolution you actually play. Gains concentrate in 1080p and 1440p titles with large textures, and can be zero or slightly negative in CPU-bound scenes.

Troubleshooting

Common issues

The Re-Size BAR option is missing from the BIOS

Update the BIOS to the newest non-beta version. On several boards the option only appears after Above 4G Decoding is saved and the firmware is re-entered.

Black screen after enabling

Clear CMOS with the jumper or the battery, boot with one memory stick, then enable Above 4G Decoding only and retry.

GPU-Z still says Disabled although the BIOS is on

The system booted in legacy mode. Check CSM is off and that the disk is GPT; some older GPU vBIOS versions also lack UEFI support.

FAQ

Frequently asked

Does every game benefit?

No. The driver keeps a whitelist; in titles without a profile the memory window stays at 256 MB.

Is enabling it risky?

It does not touch your data, but a firmware change can leave the board unbootable until CMOS is cleared. Have the clear-CMOS method ready.

How to undo this

Set **Re-Size BAR Support** and **Above 4G Decoding** back to Disabled, re-enable CSM if a legacy disk needs it, save and exit. Clear CMOS if the board stops posting.

Changelog · 1 entry
  1. 2026-10-30
    First version
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