External vs. Internal GPUs: Performance Considerations

When deciding between an internal and an external GPU for an upgrade, many factors come into play, including performance, compatibility, and convenience. While external GPUs (eGPUs) offer unparalleled flexibility and the ability to use powerful graphics cards in laptops and desktops without physical installations, they may not provide the same level of performance as an internal GPU. In this article, we will explore the differences and limitations of external GPUs, focusing on cable connections, hardware bottlenecks, and real-world performance implications.

Introduction to External GPUs

External GPUs have gained popularity in recent years, especially among professionals and gamers who require additional horsepower without the hassles of internal installations. These devices connect to your system via a Thunderbolt cable, providing a high-speed interface to the graphics processing unit. However, the performance of an eGPU is often compromised due to several factors, primarily related to the physical limitations of the connection and the inherent nature of the PCIe interface.

Cable Connections and Their Impact

The most common and widely-used connection for eGPUs is Thunderbolt, which is typically found in modern laptops and some desktops. Thunderbolt supports a wide range of applications, from high-speed data transfers to eGPU setups. However, the effectiveness of the connection is dictated by the bandwidth and the nature of the interface itself.

Thunderbolt 3 or newer can deliver up to 40 Gbps of bandwidth, but this performance can be significantly reduced when connecting an external GPU. The primary reason for this reduction is the PCIe bottleneck. When a Thunderbolt cable is used to connect an eGPU, the PCIe lanes are limited to x4 or less, which is a significant drop from the full x16 capacity of an internal GPU. This is because the Thunderbolt protocol is designed to handle not just PCIe traffic but also audio, video, and other data streams, necessitating the reduction of PCIe lanes to maintain overall system reliability and performance.

Thermal and Power Constraints of External GPUs

In addition to the bandwidth and lane limitations, external GPUs are often constrained by thermal and power considerations. External GPUs do not benefit from the same cooling system as internal GPUs, which can lead to overheating issues, especially when running on high-performance tasks. Moreover, the power delivered through a Thunderbolt cable is typically limited, often around 85W, which restricts the performance of the GPU card that can be used. Internal GPUs, on the other hand, benefit from the full power and cooling resources of the system, making them more capable in terms of performance and thermal management.

Real-World Performance Comparison

To understand the real-world performance gap between internal and external GPUs, it's essential to look at benchmark tests. When running graphic-intensive tasks such as 3D rendering, video editing, or gaming, an internal GPU generally outperforms an eGPU. The performance hit can be substantial due to the PCIe bottleneck and the lack of thermal management. However, for tasks that do not require the full potential of a high-end GPU, such as basic editing or light gaming, an eGPU can be a viable option.

One notable exception is the Linus-style setup, where the GPU is mounted internally but the fans are pushed out of the case. This setup can sometimes provide near-internal performance, bypassing some of the limitations of typical eGPUs. However, this setup is significantly more complex and requires a custom approach to airflow management within the system.

Conclusion and Final Thoughts

In conclusion, while external GPUs offer great convenience and flexibility, they do not provide the same level of performance as an internal GPU. The Thunderbolt connection, along with thermal and power constraints, limits the performance of eGPUs. For tasks that require the full potential of high-end GPU hardware, an internal installation is still the better choice. However, for users who need an eGPU for mobility or other reasons and are willing to accept a performance hit, it can still be a valuable tool in their arsenal.

When choosing between internal and external GPUs, it's important to carefully consider your specific needs and use cases. The performance gap may not always be as significant as the theoretical limits suggest, but it is there, and understanding these factors can help you make an informed decision based on your requirements.