How to Enable Resizable BAR and Why It Improves Ray Tracing Performance

Ray tracing delivers some of the most realistic lighting, reflections, and shadows in modern PC games. But achieving smooth ray-traced performance requires more than just a powerful GPU—you need to ensure your system isn’t being held back by unnecessary limitations. One of the most effective optimizations for reducing performance slowdowns, especially those caused by a ray tracing CPU bottleneck, is enabling Resizable BAR (Base Address Register).

Resizable BAR is a PCI Express technology that lets your CPU access your GPU’s full memory buffer instead of being restricted to small chunks at a time. When properly enabled, it can improve frame rates, reduce stuttering, and create a smoother ray-tracing experience. In this guide, we’ll explain how Resizable BAR works, how it combats CPU bottlenecks, and how to enable it on your system.

What Is Resizable BAR?

On older systems, CPUs are limited in how they communicate with GPUs. Traditionally, the CPU can only access 256 MB of the GPU’s VRAM at once. For modern GPUs with 8 GB, 12 GB, or even 24 GB of VRAM, that becomes a major limitation.

This is especially true for ray-traced games, where shaders, geometry, and lighting data need to be transferred quickly.

Resizable BAR removes that limitation by allowing the CPU to see and access the entire GPU memory buffer. This lets data move more efficiently between CPU and GPU, reducing latency and improving gaming performance.

For games using ray tracing—which requires rapid processing of massive amounts of data—this change can be transformative.

How Resizable BAR Helps Reduce Ray Tracing CPU Bottleneck

Many gamers focus solely on their graphics card when trying to improve ray tracing performance, but the CPU plays a much bigger role than most realize. Ray tracing requires:

• More draw calls

• Higher scene complexity

• Larger data transfers

• More computation per frame

All this puts additional stress on the CPU. When the CPU cannot keep up with the GPU’s workload, you experience a ray tracing CPU bottleneck—a situation where the GPU is underutilized simply because the CPU cannot feed it data fast enough.

Here’s where Resizable BAR helps:

1. Faster Data Transfers

By allowing full VRAM access, the CPU can deliver larger datasets to the GPU in a single pass, reducing overhead.

2. Lower Latency

With fewer communication bottlenecks, the GPU waits less for the CPU, helping stabilize frame pacing in ray-traced scenes.

3. Improved GPU Utilization

Instead of hovering at 60–70% usage during ray-traced workloads, a GPU may climb closer to 90–100% after enabling Resizable BAR.

4. Better Ray-Traced Texture and Geometry Streaming

Games that rely on real-time global illumination or path tracing benefit greatly from faster VRAM access.

For many ray-traced games, these improvements can reduce or eliminate CPU bottlenecks entirely.

How to Enable Resizable BAR on Your PC

Enabling Resizable BAR requires a compatible CPU, motherboard, and GPU. The good news is that nearly all modern systems from AMD and Intel support it.

Follow the steps below to enable it.

Step 1: Check Hardware Compatibility

Your system must meet these requirements:

CPU:

• AMD Ryzen 3000 series or newer

• Intel 10th-gen Core or newer

Motherboard:

• BIOS must support Resizable BAR / Above 4G Decoding

GPU:

• NVIDIA RTX 30/40 series

• AMD Radeon RX 6000/7000 series

If your system is from the past four years, you’re likely already compatible.

Step 2: Update Your BIOS

The next step is ensuring your motherboard BIOS is up to date.

1. Visit your motherboard manufacturer’s support page.

2. Download the latest BIOS update.

3. Follow the official flashing instructions.

This step is crucial—Resizable BAR often won’t appear unless you have the required BIOS version.

Step 3: Enable “Above 4G Decoding” and “Resizable BAR Support”

Once your BIOS is updated:

1. Reboot your PC and enter BIOS (usually Delete or F2).

2. Navigate to the Advanced, PCIe, or Boot settings.

3. Enable Above 4G Decoding.

4. Enable Resizable BAR Support.

5. Save changes and restart.

Both settings must be enabled for the feature to work.

Step 4: Enable Resizable BAR in Your GPU Driver

After enabling it in BIOS, ensure the GPU driver recognizes it.

For NVIDIA Users:

1. Open GeForce Control Panel

2. Go to System Information

3. Look for Resizable BAR: Yes

For AMD Users:

1. Open AMD Adrenalin

2. Navigate to Settings → Graphics

3. Ensure Smart Access Memory (SAM) is enabled

SAM is AMD’s branding for Resizable BAR.

How Much Performance Can You Expect?

Resizable BAR does not always provide huge performance boosts—but it can make a noticeable difference in ray-traced games, especially when the CPU is the limiting factor.

Typical gains include:

• 5–20% higher FPS

• Reduced micro-stutters

• Higher GPU utilization

Games with heavy ray-tracing workloads—Cyberpunk 2077, Alan Wake 2, Hogwarts Legacy—tend to benefit the most.

If you’ve ever noticed the GPU sitting idle while your CPU maxes out, enabling Resizable BAR is one of the easiest ways to improve the ray tracing CPU bottleneck issue.

Final Thoughts

Enabling Resizable BAR is one of the most effective ways to improve ray-traced gaming performance without buying new hardware. By reducing data-transfer limitations and boosting CPU-to-GPU efficiency, it helps eliminate bottlenecks that commonly occur in ray-traced workloads. If you’re serious about smooth lighting, shadows, and reflections, this optimization should be at the top of your list.