Imagine installing a high-end GPU on your rig, but the system restricts how much memory it can access. It’s like putting a jet engine in a car that can't fuel it fully, the performance is there, but the system can’t unlock it. That’s what happens when "Above 4G Decoding" is disabled.
What Exactly is Above 4G Decoding?
Above 4G Decoding is a BIOS setting that allows your computer's CPU to access PCI devices, like graphics cards, beyond the 4GB memory address space limit.
Think of your computer's memory addresses as a street with numbered houses. Traditionally, the addresses for all PCI devices including your graphics card, network card, and NVMe drives could only go up to number 4 billion (4GB). For older systems with less powerful hardware, this was never a problem.
However, modern graphics cards and other high-end components require a much larger address space to function efficiently, often needing more than 4GB of memory. When your system is configured to only address up to 4GB, it creates a bottleneck, preventing these devices from using their full potential.
Why is Above 4G Decoding Important?
If you’re using a system with multiple high-end graphics cards, or a server that requires large amounts of memory to be allocated to hardware devices, Above 4G Decoding can be a game-changer. By enabling this feature, you’re allowing your system to allocate more resources to these devices, which can significantly improve performance.
For example, if you’re a gamer or a video editor using multiple graphics cards, enabling Above 4G Decoding can help your system handle the heavy workload more efficiently. Similarly, if you’re running a server with a lot of hardware devices, this feature can help ensure that all devices have the resources they need to function optimally.
Who Should Enable Above 4G Decoding?
If you have a modern computer with an Intel 10th generation (or newer) or an AMD Ryzen 3000 series (or newer) CPU, and a compatible motherboard and graphics card, you should definitely consider enabling this setting.
It's particularly beneficial for:
- Gamers using high-end GPUs like the NVIDIA RTX 30/40 series or AMD RX 6000/7000 series.
- Content creators who rely on GPU-accelerated tasks.
- Users with multiple GPUs or large arrays of NVMe drives.
- Anyone looking to enable Resizable BAR for a performance uplift.
A Guide on how to Enable Above 4G Decoding
Disclaimer: This guide is intended for advanced users who are familiar with their computer's BIOS/UEFI settings. Incorrect changes can lead to system instability, boot failures, and in rare cases, data loss. Always back up your data and consult your motherboard's manual before making any changes. Proceed with caution.
Enabling Above 4G Decoding is a straightforward process, but it involves changing your BIOS settings, which can be intimidating if you’ve never done it before. Here’s a step-by-step guide:
Step 1: Restart your PC and enter the BIOS settings: How? → As the system boots up, repeatedly press the key to enter your BIOS. This is most commonly Del, F2, F10, or F12
Step 2: Once you’re in the BIOS settings, look for the “Boot”, PCI Subsystem Settings or “Advanced” tab, the exact layout can vary depending on your motherboard.
Step 3: Look for a setting called “Above 4G Decoding,” "Above 4GB MMIO," or something similar. It's usually under a menu related to PCI Express (PCIe) or I/O Ports.
Step 4: Check for Other Required Settings
Disable CSM: Many motherboards require you to disable the Compatibility Support Module (CSM) to properly enable Above 4G Decoding and Resizable BAR. This is typically found under the Boot or Security tab. Be aware that disabling CSM will prevent you from booting from older drives or devices that use a Legacy BIOS boot method.
Enable Resizable BAR: On most modern motherboards, the option for Above 4G Decoding is a prerequisite for enabling Resizable BAR. Once Above 4G Decoding is enabled, a new option for Resizable BAR may appear. You will need to enable this as well to get the full performance benefits.
Step 5: Enable Above 4G Decoding and Save Changes
Change the setting for "Above 4G Decoding" from Disabled to Enabled.
Save your changes and exit the BIOS. The option to save and exit is typically found on a top-level menu or by pressing F10
Your PC will then restart, and the changes will take effect.
Potential Issues with Above 4G Decoding
- Boot Failure: The most common issue is a system that fails to boot into the operating system. This can be caused by conflicts with the CSM (Compatibility Support Module), an older boot method that may not be compatible with the new memory mapping.
- System Instability: You might experience crashes, freezes, or other strange behavior in your operating system. This is often due to driver or device compatibility issues that can't handle the larger memory address space.
- Performance Degradation: In some cases, especially on older systems or with specific hardware/driver combinations, enabling this feature can actually lead to reduced performance. This is rare but has been reported in certain scenarios, such as with older AMD systems or specific games.
- Hardware Incompatibility: If you have any older PCI devices, such as an old sound card or capture card, they might not be compatible with Above 4G Decoding and could fail to work properly.
Troubleshooting and What to Do If Things Go Wrong
If your computer fails to boot or becomes unstable after enabling the setting, don't panic. Here's a quick plan of action:
- Clear CMOS: The easiest way to revert a bad BIOS change is to clear the CMOS. This will reset all your BIOS settings to their factory defaults. This is done by either removing the small, coin-shaped battery on your motherboard for a few minutes or by using the Clear CMOS jumper pins. Consult your motherboard manual for the exact location of these.
- Re-enter BIOS and Disable: If you can still access the BIOS, simply go back to the same menu and change "Above 4G Decoding" back to Disabled.
- Check for Driver Updates: After successfully enabling the feature, ensure you have the latest drivers for your graphics card and motherboard chipset. Outdated drivers can often be the source of instability.
- Confirm Compatibility: If you continue to have issues, verify that all your hardware (motherboard, CPU, and GPU) is officially supported for both Above 4G Decoding and Resizable BAR.
While Above 4G Decoding can provide performance benefits, it’s not without its potential issues. Some users have reported problems with booting their system after enabling this feature, particularly on older systems. If you encounter any of these problems, the first and most important step is to revert the change by disabling Above 4G Decoding in the BIOS.
Always consult your PC’s manual or manufacturer’s customer support for specific instructions related to your system.
Here is a few of them
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