Resizable BAR (Base Address Register), commonly referred to as ReBAR, is a cutting-edge PCI Express feature that permits your CPU to access the full video memory (VRAM) of your GPU directly. This advancement overcomes the old 256 MB limitation and aims to alleviate bottlenecks in data transfer between the CPU and GPU in games. When supported and properly configured, ReBAR can enhance performance in certain titles, offering a more responsive and consistent gaming experience.
How Major GPU Vendors Implement ReBAR
All three major GPU manufacturers support ReBAR, but with varying implementations. AMD was the pioneer, introducing it as Smart Access Memory (SAM) with their RX 6000 Series GPUs, allowing users to toggle it on or off globally via the Adrenalin graphics driver interface. NVIDIA followed suit, incorporating ReBAR support starting with its RTX 30 Series GPUs through a VBIOS update, although their drivers enable it only for select games. Intel’s Arc GPUs not only support ReBAR but rely on it to achieve optimal performance. While the underlying mechanism is identical across all vendors, specific implementations differ according to GPU architecture and drivers.
Enabling ReBAR on NVIDIA GPUs
NVIDIA stands apart as the only vendor that enables or disables ReBAR on a per-game basis. However, advanced users can use third-party tools, such as NVIDIA Profile Inspector, to force ReBAR for games not officially supported, possibly enhancing performance but also risking instability if the feature proves ineffective. This guide focuses on enabling Resizable BAR on NVIDIA GPUs beginning with the Ampere (RTX 30 Series) architecture, illustrating how to utilize NVIDIA Profile Inspector to activate ReBAR and assess its impact and potential drawbacks on your system.
Hands-On Performance Insights
Before attempting to enable ReBAR via NVIDIA Profile Inspector, ensure your entire system supports it at the hardware, firmware, and software levels, or it will not function regardless of driver tweaks. Essential prerequisites include a compatible NVIDIA GPU (RTX 30 Series or newer), a supporting VBIOS, and a CPU and motherboard (Intel Core 10th Gen/AMD Ryzen 3000 Series or newer) that support the feature. Even with compatible hardware, the motherboard’s UEFI BIOS must explicitly offer ReBAR settings for activation.
Ensure your motherboard’s UEFI BIOS is set to disable Compatibility Support Module (CSM), enable “Above 4G Decoding,” and then enable “Resizable BAR” or “Re-Size BAR Support.” On the software side, use a modern operating system like Windows 10 or 11, installed in UEFI mode, and keep your UEFI BIOS and drivers up to date.
Once these conditions are met, NVIDIA Profile Inspector can be used to force-enable ReBAR for unsupported titles, allowing for benchmarking and tuning. You must first ensure that your entire system supports it at the hardware, firmware, and software levels. The NVIDIA Profile Inspector tool is a portable utility for viewing and editing hidden NVIDIA driver settings, including ReBAR flags. After downloading and extracting the tool, run it as an administrator, ensuring you have .NET Framework 4.0 or higher installed if prompted.
With the latest NVIDIA Profile Inspector build, you can explore various ReBAR settings that may offer further performance boosts or stability enhancements. For instance, tweaking the “Size Limit” setting can improve performance and reduce stuttering in games like FINAL FANTASY VII REBIRTH.
The benchmarks demonstrate that Resizable BAR can provide notable performance improvements, especially in games with significant data streaming or complex worlds. The mixed results across different systems, like desktop and laptop PCs, indicate that factors such as CPU generation, GPU architecture, and game settings can influence ReBAR’s effectiveness. Benchmarking your system with realistic settings is essential to determine whether ReBAR offers a net benefit.
However, enabling ReBAR manually via NVIDIA Profile Inspector isn’t without risks, especially in non-whitelisted games. Issues like system freezes, stuttering, or performance regressions may occur in some titles, highlighting the need for cautious testing and possible rollback if problems arise.
PCIe Resizable BAR can unlock performance improvements in the right scenarios, offering higher average framerates and smoother gameplay without additional hardware investment. For NVIDIA GeForce RTX 30 Series and newer GPU owners, tools like NVIDIA Profile Inspector provide the flexibility to test ReBAR’s effectiveness for your setup and favorite games. However, due to the potential for instability or performance issues, objective benchmarking is crucial to assess the impact of this driver tweak.