Above 4G Decoding should generally be turned on on computers with modern 64-bit systems, discrete graphics cards, or multiple PCIe expansion cards. It allows the firmware to put part of the MMIO/BAR resources required by the device into the address space above 4GB, reducing the problem of multiple devices competing for low address space.
Under what circumstances is it recommended to enable it?
- There is a discrete graphics card and the motherboard provides Resizable BAR / SAM options.
- Use multiple graphics cards, HBAs, SATA expansion cards, high-speed network cards, or other PCIe devices.
- The NAS or workstation has been expanded a lot, and has experienced device disappearance, insufficient resources, or abnormal startup.
- System is modern 64-bit Windows or Linux with newer motherboard and device firmware.
It’s not a switch that improves CPU performance, nor does it guarantee that all games or applications will be faster; its main purpose is to improve device address resource allocation. For concepts and MMIO/BAR principles, see What is Above 4G Decoding.
Relationship with Resizable BAR
Many motherboards will require Above 4G Decoding to be turned on before allowing Resizable BAR to be turned on. The former can be understood as preparing the address space for a wider range of device mapping, while the latter allows the CPU to access the graphics card BAR more flexibly. The two are related, but not identical.
Where is it usually located in BIOS?
The name may vary slightly from brand to brand, usually under Advanced, PCIe, Chipset, or similar menu, and may also be placed with Resizable BAR. Before modifying, take a photo to record the current value, and confirm the motherboard manual or firmware update instructions; do not blindly change other PCIe options just because the screenshots online are the same.
What to do if it cannot be started after being turned on?
Turn off the power first and restore the default BIOS settings according to the motherboard manual, such as using Clear CMOS or restoring default options. Then gradually change back to Above 4G Decoding only to confirm whether it is related to the old graphics card, expansion card, BIOS version or other compatibility settings. Do not stack multiple BIOS changes in succession without confirming the cause.
For local models or NAS expansion scenarios, graphics card memory, PCIe slot bandwidth, cooling, and power should also be checked separately; Above 4G Decoding is not a replacement for these bottlenecks. For video memory selection, please refer to [RTX 3060 running Qwen3 quantization and video memory selection] (/en/2026/07/11/rtx-3060-qwen3-best-quantization-guide/).
Summary
In modern 64-bit systems, independent graphics and multiple PCIe device environments, Above 4G Decoding is mostly worth turning on; when old hardware or startup abnormalities occur, keep the path to restore the BIOS and verify compatibility item by item.
Confirm these prerequisites before modifying
Above 4G Decoding works on modern UEFI and 64-bit systems. If your machine is still using legacy boot mode, a very old expansion card, or a BIOS version, read the motherboard support notes and update to stable firmware first; don’t mix new settings with multiple unrelated overclocking and memory timing changes in one operation.
Recommendations before modification: record the current BIOS page, confirm the location of clear CMOS or motherboard recovery method, ensure stable power supply, and operate when there is no emergency work. This allows you to return to a known state even if the screen goes black or the device is not recognized.
A low-risk setup step
- Enter the BIOS and find Advanced, PCIe, Chipset or a menu similar to Resizable BAR.
- Only enable Above 4G Decoding, save and start the system.
- Confirm that the graphics card, network card, HBA or SATA expansion card are recognized in the system.
- If necessary, enable Resizable BAR/SAM and repeat the verification.
- Use it continuously for a period of time and observe whether sleep wake-up, restart, virtualization and heavy load are normal.
It is important to verify the two switches separately. If you change multiple PCIe options at once, it can be difficult to know later which one is causing the compatibility issue.
How to judge common phenomena
| Phenomenon | Possible directions | Priority processing |
|---|---|---|
| The device disappears from the system | Resource allocation or slot compatibility | Test card by card after restoring to default |
| Black screen after turning on | BIOS/graphics card compatibility or startup settings | Clear CMOS, update firmware |
| ReBAR option gray | Prerequisites not met | Check UEFI, graphics card and BIOS |
| NAS expansion card is unstable | Slot bandwidth, power supply or driver | Don’t just keep an eye on the switch |
What it doesn’t solve
Above 4G Decoding does not increase video memory, increase the physical bandwidth of PCIe slots, or repair underpowered, overheated, or damaged expansion cards. When the local large model cannot run, you should still check the model quantization, video memory, memory and context first; when the NAS cannot recognize the hard disk, you should also check the HBA chip, cables, power supply and driver.
Recommendations for multiple graphics cards and NAS
Multi-graphics workstations should pay particular attention to motherboard CPU channels, slot sharing rules and power margins. When adding HBA or multiple NVMe to the NAS, you also need to look at the chipset channels and heat dissipation; being able to turn on Above 4G Decoding only means that the address space pressure may be alleviated, but it does not mean that the overall machine expansion plan is reasonable.
FAQ: Do I need to enable it if I only have one graphics card?
If it’s a modern 64-bit UEFI platform and there are no compatibility issues, this can usually be turned on; but without ReBAR or extended device requirements, the performance difference may not be noticeable.
FAQ: Will turning it on damage the hardware?
Normally not. It is a firmware resource allocation option; the risk mainly comes from old device compatibility or modifying too many BIOS items at the same time resulting in failure to boot, which can be handled by following the recovery steps.