Technology
Oct 03, 2026
2 min read
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Multi-GPU Setup and BIOS Patching for Resizable BAR on Z270 Hardware
Running modern graphics cards on older architectures often runs into firmware limitations. Motherboards of the LGA1151 generation, such as the ASUS TUF Z270 Mark 1, do not provide native support for the RESIZABLE BAR (ReBAR) — an essential feature for Intel Arc cards.
This guide explains how to modify and patch an AMI UEFI BIOS to enable Above 4G Decoding and Resizable BAR options, enabling simultaneous operation of Intel Arc A770 and NVIDIA Quadro P4000 cards on a Z270 chipset. 1. Preliminary Requirements and Tools
Before modifying the firmware, make sure you have the rewriting and patching tools ready:
UEFIPatch / ReBarUEFI: Tool for inserting UEFI modules responsible for PCI BAR allocation.
AMI Firmware Update (AFU) Tool / Flashrom: For reading and writing BIOS image. Hardware programmer (e.g. CH341A): Recommended as a safety solution for recovery in case of a failed write. 2. Extracting and Patching the UEFI Image
Saves the existing BIOS image or downloads the latest official version (Z270-TUF-MARK1-ASUS-XXXX.CAP).
If you're using an Asus .CAP file, remove the 2048-bit capsule header using a hexadecimal editor or ReBarImageBuilder to get the raw ROM file. Run the ReBarUEFI utility to modify the PciHostBridgeDxe module:
Bash
# Run UEFIPatch on extracted raw BIOS file
./UEFIPatch Z270RAW.bin patches.txt -o Z270_ReBAR.bin
Check in the output log if the PCI structure has been successfully replaced:
Plaintext
Patching PciHostBridgeDxe modules...
Offset: 0x1A2B3C -> Replaced successfully. 3. Rewriting the BIOS and Configuration
Rewrites the modified image using Asus USB BIOS Flashback (ignoring official signature verification) or modified flash utilities.
After rewriting, perform a CMOS reset, enter the BIOS settings and configure the PCI subsystem:
Above 4G Decoding: Enabled
PCIe Speed: Set slots 1 and 2 to Gen3
CSM (Compatibility Support Module): Disabled (Pure UEFI mode is mandatory for ReBAR)
4. Verification in the Operating System (Linux / Windows)
Starts the system and checks the allocation of PCI resources for both graphics cards.
On Linux
Bash
# Check PCIe BAR memory sizes
lspci -v -s 03:00.0 | grep -i "Memory at"
Look for memory allocations exceeding 256M for Intel Arc card (usually 8G or 16g). On Windows
Run the ReBarState.exe executable on the command line to check the active BAR size:
DOS
ReBarState.exe
The result should display: Resizable BAR enabled with BAR size 16384 MB.
This guide explains how to modify and patch an AMI UEFI BIOS to enable Above 4G Decoding and Resizable BAR options, enabling simultaneous operation of Intel Arc A770 and NVIDIA Quadro P4000 cards on a Z270 chipset. 1. Preliminary Requirements and Tools
Before modifying the firmware, make sure you have the rewriting and patching tools ready:
UEFIPatch / ReBarUEFI: Tool for inserting UEFI modules responsible for PCI BAR allocation.
AMI Firmware Update (AFU) Tool / Flashrom: For reading and writing BIOS image. Hardware programmer (e.g. CH341A): Recommended as a safety solution for recovery in case of a failed write. 2. Extracting and Patching the UEFI Image
Saves the existing BIOS image or downloads the latest official version (Z270-TUF-MARK1-ASUS-XXXX.CAP).
If you're using an Asus .CAP file, remove the 2048-bit capsule header using a hexadecimal editor or ReBarImageBuilder to get the raw ROM file. Run the ReBarUEFI utility to modify the PciHostBridgeDxe module:
Bash
# Run UEFIPatch on extracted raw BIOS file
./UEFIPatch Z270RAW.bin patches.txt -o Z270_ReBAR.bin
Check in the output log if the PCI structure has been successfully replaced:
Plaintext
Patching PciHostBridgeDxe modules...
Offset: 0x1A2B3C -> Replaced successfully. 3. Rewriting the BIOS and Configuration
Rewrites the modified image using Asus USB BIOS Flashback (ignoring official signature verification) or modified flash utilities.
After rewriting, perform a CMOS reset, enter the BIOS settings and configure the PCI subsystem:
Above 4G Decoding: Enabled
PCIe Speed: Set slots 1 and 2 to Gen3
CSM (Compatibility Support Module): Disabled (Pure UEFI mode is mandatory for ReBAR)
4. Verification in the Operating System (Linux / Windows)
Starts the system and checks the allocation of PCI resources for both graphics cards.
On Linux
Bash
# Check PCIe BAR memory sizes
lspci -v -s 03:00.0 | grep -i "Memory at"
Look for memory allocations exceeding 256M for Intel Arc card (usually 8G or 16g). On Windows
Run the ReBarState.exe executable on the command line to check the active BAR size:
DOS
ReBarState.exe
The result should display: Resizable BAR enabled with BAR size 16384 MB.