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Unleashing Full GPU Power: The Magic of Resizable BAR and Smart Access Memory.

In the world of gaming and high-performance computing, every edge counts. Two technologies, Resizable BAR (Base Address Register) and Smart Access Memory (SAM), have recently gained attention for their ability to enhance system performance, particularly in gaming scenarios. But what exactly are these technologies, how do they work, and how can you enable them on your system? Let’s delve into the details. It’s incredible a quick adjustment in the BIOS of your system can bring so significant performance improvements in most applications & games.

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What Are Resizable BAR and Smart Access Memory?

Resizable BAR is a PCI Express (PCIe) feature that allows the CPU to access the GPU’s entire video memory (VRAM) rather than being limited to small chunks of 256MB at a time. This broader access can improve data transfer efficiency and reduce bottlenecks, leading to enhanced performance in certain workloads.

Smart Access Memory (SAM) is AMD’s branding for its implementation of Resizable BAR. While the underlying technology is the same, SAM is specifically optimized for AMD hardware, including Ryzen processors and Radeon GPUs, ensuring compatibility and streamlined performance benefits.

History of Resizable BAR and SAM

Resizable BAR traces its origins to the PCI Express 2.0 specification, which introduced the ability for CPUs to map the entire VRAM into their addressable memory space. However, due to limited use cases and a lack of software optimization, this feature went largely unnoticed until the rise of modern gaming and high-performance workloads. It was NVIDIA’s and AMD’s recent adoption and optimization of Resizable BAR that brought it into the spotlight, enabling improved performance for GPUs in demanding scenarios.

AMD first introduced Smart Access Memory alongside the launch of their Radeon RX 6000 series GPUs in late 2020. Initially exclusive to AMD hardware, SAM required a combination of a Ryzen 5000 series CPU, a Radeon RX 6000 GPU, and a 500-series motherboard. NVIDIA quickly followed suit, implementing Resizable BAR support across their GeForce RTX 30-series GPUs in early 2021. Intel joined the trend as well, integrating support into their 11th Gen CPUs and later platforms.

Performance Metrics of Resizable BAR and SAM

The performance improvements from Resizable BAR and SAM vary depending on the workload, game, and hardware configuration. On average, users can expect gains ranging from 5% to 15% in supported applications and games. Certain titles optimized for this technology, such as Forza Horizon 5 or Cyberpunk 2077, may see even higher boosts, particularly at higher resolutions like 1440p and 4K, where the CPU-GPU data exchange becomes critical.

It’s worth noting that the effectiveness of Resizable BAR and SAM depends on game optimization. Some games show little to no benefit, while others see marked improvements, especially those with high VRAM usage or frequent texture streaming. Additionally, enabling Resizable BAR requires both hardware and BIOS compatibility, as well as driver support, emphasizing the need for up-to-date systems.

How Do They Work?

Traditionally, the CPU could only access the GPU’s VRAM in 256MB segments due to legacy limitations. This approach created inefficiencies, especially for modern games and applications that require rapid and large-scale data transfers between the CPU and GPU.

This segmentation arose from the original PCI Express Address Space limitations, where the Base Address Registers (BARs) used to map GPU memory to the CPU’s addressable memory space were designed for smaller workloads in earlier computing architectures. While sufficient for older applications, this piecemeal approach became a bottleneck as modern workloads began to demand larger and more seamless data pipelines.

Resizable BAR and SAM lift this restriction by allowing the CPU to map and access the entire VRAM buffer directly. By leveraging 64-bit addressing and advanced PCIe memory-mapping features, this implementation eliminates the need for fragmented data transactions, enabling continuous access to the GPU’s memory. This reduces overhead in the memory controller, minimizes latency, and significantly enhances data throughput.

In practice, this change is particularly advantageous for scenarios where large datasets need to be transferred and processed quickly. For example:

1. Real-Time Texture Streaming: Modern games rely on high-resolution textures that must be dynamically loaded and unloaded as players move through complex environments. Resizable BAR allows the CPU to request and stream these assets more efficiently, preventing stutters and reducing frame-time inconsistencies.
   
2. AI and Computational Workloads: Workloads like AI inference, ray tracing, or GPU-accelerated rendering benefit from the reduced latency and higher bandwidth provided by Resizable BAR, enabling faster data exchange between the CPU and GPU.
   
3. Multi-GPU Systems: In multi-GPU setups, Resizable BAR enables smoother communication and load balancing between GPUs by improving the data-handling capabilities of the CPU, enhancing scalability.

It’s important to note that the practical performance benefits of Resizable BAR and SAM are contingent on several factors, including game engine support, system hardware configuration, and the efficiency of PCIe and driver implementations. Additionally, optimal results are observed in workloads that maximize GPU VRAM usage or require frequent CPU-GPU communication.

Are They the Same Thing?

While Resizable BAR and SAM are based on the same PCIe specification, the distinction lies in branding, optimization, and ecosystem-specific implementation:

1. Resizable BAR: This is a standard PCI Express feature outlined in the PCIe 2.0 and later specifications. It allows for a configurable base address register size, enabling the CPU to map the GPU’s entire VRAM buffer instead of the traditional 256MB segments. Resizable BAR is a vendor-agnostic feature, supported by both AMD and NVIDIA GPUs, provided the hardware, firmware (BIOS/UEFI), and drivers are configured to enable it.
   
2. Smart Access Memory (SAM): AMD’s proprietary branding for its implementation of Resizable BAR, SAM takes advantage of AMD’s vertically integrated ecosystem. Specifically optimized for Ryzen processors and Radeon GPUs, SAM ensures compatibility and efficiency by leveraging AMD’s shared development framework. This streamlined approach reduces the likelihood of performance variability, as the feature is designed with AMD hardware configurations in mind.

For users utilizing Intel CPUs and NVIDIA GPUs, Resizable BAR offers an equivalent feature set. However, its implementation depends on hardware and driver compatibility rather than ecosystem-specific optimizations. Intel introduced Resizable BAR support starting with their 11th Gen CPUs and compatible motherboards, while NVIDIA enabled the feature on GeForce RTX 30-series GPUs via a firmware update.

Although not branded as “SAM,” the functionality is effectively the same, allowing for direct VRAM access and performance gains in supported applications. In practical terms, AMD’s SAM often benefits from tighter integration within its ecosystem, potentially reducing variability in performance gains. By contrast, Resizable BAR implementations across mixed-vendor setups, such as Intel CPUs paired with NVIDIA GPUs, might require additional tuning through BIOS settings, driver updates, and firmware patches to achieve similar levels of optimization.

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Hardware Requirements

To leverage Resizable BAR or SAM, you’ll need:

1. Motherboard: A compatible motherboard with UEFI firmware that supports Resizable BAR.
2. CPU: A processor that supports the technology (e.g., AMD Ryzen 3000/5000 series or Intel 10th/11th Gen and newer).
3. GPU: A graphics card with firmware support for Resizable BAR. AMD’s RDNA2 GPUs (Radeon RX 6000 series and newer) and NVIDIA’s Ampere and newer GPUs support this feature.
4. BIOS/Driver Updates: Updated motherboard BIOS and GPU drivers to enable the feature.

Performance Benefits for Gamers

The performance benefits of Resizable BAR and SAM are influenced by several factors, including the game engine, resolution, and specific hardware configuration. The degree of improvement is contingent on how effectively the underlying workload can leverage the broader VRAM access these technologies enable:

1. General Performance Gains: In most cases, enabling Resizable BAR or SAM results in a measurable performance uplift, typically in the range of 5-10%, with some outlier titles achieving even greater improvements. This increase stems from the reduction in CPU-to-GPU communication latency and the enhanced efficiency of large-scale data transfers.
   
2. Game-Specific Benefits: Games that involve frequent and large data transactions, such as open-world titles or those with expansive textures and real-time asset streaming, often see the most significant improvements. For example, titles like Forza Horizon 5 or Red Dead Redemption 2 can benefit substantially due to their heavy reliance on texture streaming and dynamic environment loading.
   
3. Resolution Dependency: Higher resolutions, particularly 1440p and 4K, stand to gain more from Resizable BAR and SAM because they inherently demand greater bandwidth and exhibit more pronounced CPU-GPU communication bottlenecks. The increased VRAM utilization at these resolutions makes the technology’s ability to streamline access to large memory buffers particularly impactful, reducing stutters and improving frame-time consistency.

While Resizable BAR and SAM deliver clear advantages in optimal scenarios, their performance impact can vary based on factors such as game optimization and hardware support. Some titles may show negligible improvement if they are not designed to exploit the broader memory access, underscoring the importance of software-level optimization for maximizing the benefits of these technologies.

Benchmarks

• AMD SAM Benchmarks:
  • Assassin’s Creed Valhalla: +15% performance increase at 1440p on an AMD Ryzen 5000 series CPU and Radeon RX 6800 XT.
  • Cyberpunk 2077: +8% performance improvement at 4K with SAM enabled on the same hardware configuration.
    
• NVIDIA Resizable BAR Benchmarks:
  • Watch Dogs: Legion: +7% boost at 1440p on an Intel Core i7-11700K and NVIDIA RTX 3080.
  • Forza Horizon 5: +12% gain at 4K on an AMD Ryzen 7 5800X and NVIDIA RTX 3070.

These benchmarks demonstrate that the performance uplift varies by title and resolution, with open-world and resource-heavy games benefiting the most.

Game Compatibility

Games do not require specific programming to “support” Resizable BAR or SAM, as these technologies function at the hardware and driver level, enabling seamless access to the GPU’s full VRAM buffer. However, the magnitude of performance improvements depends heavily on how the game engine manages data streaming and memory access.

Modern game engines that rely on frequent texture streaming, dynamic asset loading, or large-scale world generation are inherently better positioned to benefit from these technologies. For instance, engines designed to pre-fetch and process large datasets can effectively utilize the reduced latency and increased bandwidth provided by Resizable BAR and SAM, leading to smoother gameplay and reduced frame-time inconsistencies.

To fully exploit these benefits, developers can take additional steps to optimize their games specifically for these features, such as:

1. Streamlining Asset Pipelines: Adjusting asset loading mechanisms to take advantage of continuous memory access can reduce texture pop-in and stuttering, particularly in open-world or graphically intensive games.
   
2. Optimizing Data Streaming: Implementing techniques that leverage the higher data throughput enabled by Resizable BAR and SAM can improve performance during complex scenes with high memory demands.
   
3. Fine-Tuning VRAM Allocation: By optimizing memory allocation strategies to match the capabilities of Resizable BAR and SAM, developers can minimize overhead and maximize resource utilization.

While not a strict requirement, optimization efforts can magnify the performance gains offered by these technologies, ensuring a more consistent and responsive experience for players. Without such optimizations, the improvements may vary depending on how effectively the game’s existing architecture can leverage broader memory access.

How to Enable Resizable BAR and SAM

For AMD GPUs:

1. Update BIOS: Ensure your motherboard’s BIOS is updated to a version that supports Resizable BAR.
2. Enable in BIOS: Enter the BIOS settings and enable Resizable BAR (may also be listed as Above 4G Decoding).
3. Install Drivers: Update to the latest AMD GPU drivers that support SAM.
4. Check in Radeon Software: Use the AMD Radeon Software to verify that SAM is enabled.

For NVIDIA GPUs:

1. Update BIOS: Ensure your motherboard and GPU firmware are updated for Resizable BAR support.
2. Enable in BIOS: Access the BIOS and enable Resizable BAR.
3. Install Drivers: Update to the latest NVIDIA GPU drivers.
4. Verify in NVIDIA Control Panel: Open the NVIDIA Control Panel to confirm Resizable BAR is active.

How to Check if Your System Supports or Has Enabled SAM/Resizable BAR

1. AMD GPUs:
   • Open the AMD Radeon Software.
   • Navigate to the Performance tab, then click on the Tuning or System options.
   • Look for “Smart Access Memory” and check its status.
2. NVIDIA GPUs:
   • Open the NVIDIA Control Panel.
   • Go to the System Information section.
   • Check for Resizable BAR status.

Performance Gains and Configurations

While the average performance gain from Resizable BAR and SAM is modest, specific configurations and scenarios can yield standout improvements:

1. AMD Ecosystem: Systems featuring Ryzen CPUs paired with Radeon GPUs experience the most significant performance benefits due to AMD’s tightly integrated and optimized implementation of Smart Access Memory (SAM). This ecosystem-level synergy minimizes overhead and ensures compatibility, allowing for more consistent and efficient utilization of the broader memory access enabled by SAM.
   
2. High-Resolution Gaming: Resolutions like 1440p and 4K inherently demand greater data throughput due to the increased size and complexity of rendered frames. In these scenarios, the enhanced bandwidth and reduced latency offered by Resizable BAR and SAM can result in more noticeable performance gains, improving frame rates and reducing stutters during graphically intensive scenes.
   
3. Bandwidth-Intensive Games: Titles that rely heavily on large textures, frequent asset streaming, or dynamic world loading see the greatest improvements. Open-world games, simulation titles, and ray-traced environments often fall into this category, as they involve substantial data transfer between the CPU and GPU. By leveraging the unrestricted VRAM access provided by Resizable BAR and SAM, these games can deliver smoother performance and faster asset loading.

While these configurations and use cases highlight the potential of Resizable BAR and SAM, the actual performance uplift remains contingent on game engine optimizations, driver support, and hardware compatibility. In well-optimized environments, the impact can be transformative, particularly for gamers and professionals pushing their systems to handle demanding workloads.

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Conclusion

Resizable BAR and Smart Access Memory represent significant steps forward in maximizing the performance potential of modern hardware. By removing traditional bottlenecks in data transfer, these technologies provide gamers with smoother and more responsive experiences. While the performance gains vary, the benefits are particularly pronounced in certain games and configurations.

Enabling these features is straightforward and worth exploring for anyone with compatible hardware. Whether you’re on Team AMD or Team NVIDIA, taking advantage of Resizable BAR or SAM can give you that extra edge you’re looking for. I hope you found this blog informative.

Please let me know in the comments if you found the performance benefits of resizable bar worthwhile in your gaming and flight simulators……. Welcome to my Blog LetsFlyVFR.com. Lots more to discover click here to go to the front-page end dive further unto the world of Flight Simulation & Associated tech news.

Author

Brendon McAliece (Aka Gunnie) is a military veteran with 23 years working on Jet Fighters, their weapons systems and ejection seat/module systems as well as munitions and R&D. Involved with flight simulation since the 1980s, he has flown all the major flight simulators over the years.

He is an Australian expat who has lived in Malaysia, UK, Saudi Arabia and more recently Thailand. He is a multi-lingual blogger who loves to share his life experiences here on LetsFlyVFR.com and DreamingGuitar.com, with his lifestyle and Travel experiences Blog plus his Dreaming Coffee website.

Learn More @ DreamingGuitar.com – DreamingCoffee.com – LetsFlyVFR.com

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