In context: For those unfamiliar with OCuLink, it is an optical interface developed over a decade ago, primarily for servers. However, it has recently gained attention for consumer uses, such as external GPUs. OCuLink offers higher bandwidth compared to Thunderbolt 4 – up to 64 Gbps versus 40 Gbps. This increased bandwidth opens up the possibility better eGPU performance compared to Thunderbolt.

Nvidia's RTX 4090 is a powerhouse GPU, but how much performance is lost when you dock it as an external graphics card due to the interface's limitations? A Chinese tech enthusiast website put it to the test to find out. The results are surprising and show the potential and challenges of OCuLink for external graphics.

The RTX 4090 was tested in 3DMark over an OCuLink eGPU dock connected to a laptop with Intel's new Core Ultra 5 125H processor. With the internal laptop display, there was a 23% performance hit in Time Spy and 5% in Time Spy Extreme compared to the desktop. But with an external display, the losses dropped to 17% and 0%.

The story was similar with the RTX 4070 Ti, with a 10% loss over OCuLink to internal display, but using external monitor regained most performance. This shows OCuLink's higher bandwidth can better feed these hungry GPUs, especially paired with an external display.

The reason the external monitor improves performance is that it reduces the burden on OCuLink's bandwidth. Pushing frames back to the internal laptop screen eats up bandwidth that could otherwise go to the GPU. With an external display, more bandwidth is available for the GPU to stretch its legs.

It's also noted that Time Spy Extreme showed less of a performance hit than Time Spy, likely because its higher frame rate leads to more GPU-system communications per frame. This further burdens the interface bandwidth. Lower resolutions or frame rates will tax the connection less.

While there is still a noticeable performance hit over OCuLink versus having the GPU installed on a desktop PC, it's an interesting option for adding serious GPU power to thin laptops or mini PCs without discrete graphics. Products like the GPD Win Max 2 and upcoming eGPU docks are bringing OCuLink to consumers.

With Thunderbolt 5 on the horizon, offering up to 80Gbps of bandwidth, the eGPU market is set to become even more competitive. Currently, OCuLink serves as an alternative to Thunderbolt, particularly with its higher bandwidth. However, Thunderbolt's broader adoption may give it an advantage, so it remains to be seen how much traction OCuLink can gain before Thunderbolt 5 becomes available.

In the end, this RTX 4090 benchmark shows OCuLink's potential for external graphics, albeit with certain compromises. As always with eGPUs, managing expectations is key. For many uses though, the performance may be "good enough" for ultraportable gaming or content creation. We'll have to wait and see if OCuLink can carve out a space in the (somewhat) evolving eGPU landscape.