Thunderbolt is an incredibly powerful and versatile connector that can deliver a lot of bandwidth for USB devices, displays, and even external GPUs, on top of supporting power delivery. This wide range of capabilities, and the fact that it's maintained by Intel, which has mostly dominated the PC processor market, makes it a very popular technology.

But when it comes to external GPUs, an up-and-coming rival in the form of OCuLink has been making waves, and it actually shows how Thunderbolt can be something of a bottleneck. If you're heavily invested in external GPUs, OCuLink may be a better solution for you.

The good and bad of Thunderbolt

Versatile, but limited

As mentioned above, the big benefit of Thunderbolt over other connectors is its sheer versatility. A Thunderbolt port can handle USB data, video output, and PCIe tunneling for very fast connections across the board. In Thunderbolt 4, which is still the most popular version of the connector, the total bandwidth of the connection is 40Gbps, which is plenty to work with. In Thunderbolt 5, this was doubled to 80Gbps of bi-directional bandwidth, though a special mode also allows up to 120Gbps bandwidth in a single direction.

However, that bandwidth is shared for all of the connections Thunderbolt allows to pass through it, and only a subset of it can be reserved for PCIe tunneling, which is what you need for an external GPU to work. Thunderbolt 4 supports PCIe tunneling up to 32Gbps, which is equivalent to a PCIe 3.0 x4 connection. Thunderbolt 5 upgraded to PCIe 4.0 x4, so now you get up to 64Gbps.

However, Thunderbolt 5 availability is extremely limited, and this can be an expensive technology to include in a product. Intel says Thunderbolt is royalty-free, but there's probably a reason why devices with Intel processors almost always have a Thunderbolt port, while PCs powered by AMD rarely ever get Thunderbolt support. And with the extra costs of Thunderbolt 5, that's even more prevalent. It's already rare for any PC to have Thunderbolt 5 support (you'll see it in workstations and high-end gaming laptops), but even more so for AMD-based machines.

There's also a degree of latency introduced by the Thunderbolt controller in an eGPU dock, and that could get even worse if you use the extra ports in an eGPU dock, which requires more bandwidth.

OCuLink is more focused

GPUs can be faster

The problems with Thunderbolt aren't a new concern, and a solution started emerging some time ago with OCuLink, which is short for "Optical-Copper Link". This lesser-known connection is exclusively focused on supporting GPUs through PCIe signaling, so it doesn't support USB data or power passthrough, which makes it a little less versatile and more complicated to set up, but comes with a significant performance benefit.

Most OCuLink connections have always supported PCIe 4.0 x4, which meant you could get double the bandwidth as Thunderbolt 4, with which OCuLink co-existed for a good while. It's also the same as what Thunderbolt 5 promises, but the focus on PCIe signaling alone may still offer performance benefits in real-life usage.

Technically, OCuLink can actually support up to 8 lanes of PCIe communication, which would still be double of what Thunderbolt 5 can offer, though we haven't seen any implementations of this in an eGPU dock yet.

The limitations of Thunderbolt aren't something companies are oblivious to, and OCuLink isn't even the only solution for it, but it is the most open one. The Asus ROG Ally initially shipped with a proprietary connector, and I've reviewed a mini PC called Khadas Mind that also uses a proprietary connector to connect to an external GPU with faster performance than Thunderbolt. In 2024, Lenovo's ThinkBook 14i Gen 6+ also used a connector similar to OCuLink to support the proprietary ThinkBook Graphics Extension add-on.

OCuLink is just a more open approach that has been supported by a lot of gaming handhelds and mini PCs. Unfortunately, it hasn't gained a lot of traction among major PC manufacturers, though. You'll see it from brands like One Xplayer, Geekom, Minisforum, and others making relatively low-key computers.

How much faster is OCuLink?

It makes a big difference

Talking about numbers is one thing, but how do these differences affect real-life performance? Well, I tried using an OCuLink GPU with a Minisforum mini PC a while back, and the results were very significant. Using the same GPU over Thunderbolt 4 and OCuLink showed a very significant improvement in bandwidth for the GPU in 3DMark, going from 2.42GB/s via USB4 (Thunderbolt 4) to 6.70GB/s via OCuLink.

That translated to a pretty noticeable difference in in-game performance, too. While it will depend on what games you're playing, as well as things like your target resolution and texture quality, OCuLink just offers a smoother experience across the board. In some games, like Shadow of the Tomb Raider (seen above), the average frame rate is only slightly higher, but it's when you look at the 99% and 99.9% percentile that you see far fewer spikes and variations, leading to a smoother feeling experience overall.

In a game like Forza Horizon 5, though, I was able to nearly double the frame rate, and Elden Ring also showed massively improved performance in my testing.

Due to the scarcity of Thunderbolt 5-enabled PCs and eGPUs, I haven't been able to compare it directly to OCuLink yet, but it's worth keeping in mind that, when comparing Thunderbolt 4 and OCuLink, the bandwidth more than doubled in real-life tests, even though it should only have doubled according the specifications on paper. While Thunderbolt 5 has the same speeds on paper as OCuLink, there's a reasonable possibility that OCulink would still come out on top in real-life scenarios.

Will OCuLink be more widely supported?

Probably not

For all those benefits, though, I'm afraid OCuLink will always be a more niche technology than Thunderbolt for multiple reasons. For one thing, Thunderbolt has Intel's backing, and Intel has very strong relationships with PC manufacturers, which can be used to encourage companies to include those ports more often.

Thunderbolt is also a much smaller connector, since it just uses USB-C, whereas OCuLink is a significantly larger proprietary port. In a world where many laptops get rid of HDMI, USB Type-A, and sometimes even headphone jacks, a big port like OCuLink is always going to be a specialty inclusion, not something for the masses.

Plus, as I've mentioned, Thunderbolt is more versatile and handles a lot more than just GPUs, so it makes more sense to include that compared to a port that leaves your laptop still needing extra ports for USB data or charging. OCuLink ultimately makes the most sense in something like a mini PC where there's more space for ports, but that's about it.

That doesn't mean OCuLink is better or worse than Thunderbolt, but rather, these technologies can coexist for different target markets. If leveraging an eGPU for maximum performance is your goal and you're invested in that idea, OCuLink makes a lot more sense, but for most people, Thunderbolt is just the easy choice. Niche enthusiast products don't have to stop exist just because they're niche enthusiast products, and I'd certainly love to see OCuLink continue to evolve with newer PCIe standards and even higher bandwidth.