An external GPU (eGPU) puts a desktop graphics card in a separate enclosure connected to a laptop or mini PC. The link is the bottleneck, and the two common options are OCuLink and Thunderbolt/USB4.
What is OCuLink?
OCuLink (Optical-Copper Link) is a PCI-SIG standard for carrying PCIe over a cable. Common eGPU setups use SFF-8611 on the host and SFF-8612 on the device, with 4 PCIe lanes at 8 GT/s (PCIe 3.0) or 16 GT/s (PCIe 4.0), up to 64 Gbps. It carries only PCIe: no DisplayPort, USB or power (ChargerLAB/OCuLink.net: what OCuLink products work with external graphics cards).
OCuLink vs Thunderbolt
| Link | Max PCIe bandwidth | Also carries | Source |
|---|---|---|---|
| Thunderbolt 4 | 32 Gbps | USB, DisplayPort, power | Intel: Thunderbolt messaging guide (bandwidth claims) |
| Thunderbolt 5 | 64 Gbps | USB, DisplayPort, power (80 Gbps total, 120 Gbps in one direction) | Intel: Thunderbolt messaging guide (bandwidth claims) |
| OCuLink (PCIe 4.0 x4) | 64 Gbps | PCIe only | ChargerLAB/OCuLink.net: what OCuLink products work with external graphics cards |
In third-party testing reported by TechPowerUp, an RTX 5070 Ti over OCuLink averaged up to about 16% higher gaming performance than over Thunderbolt 5, and about 7–8% below a direct motherboard slot (TechPowerUp: OCuLink vs Thunderbolt 5 eGPU testing (reporting Try Some Tech)). These are someone else's results, not our measurements.
eGPU enclosure checklist
- Port on your laptop or mini PC: OCuLink is rare on laptops; Thunderbolt/USB4 is more common.
- Card length, slot width and power connectors the enclosure accepts.
- Power supply included, and its wattage vs the card maker's recommendation.
- OCuLink has no hot-swap (per TechPowerUp's summary); connect before booting.
eGPUs for local AI
In principle, once a model is fully loaded into the card's VRAM, the link speed matters less for generating text than for loading the model, so an eGPU can add usable VRAM to a mini PC. Measured AI results over eGPU links: TBD. Check fit with Can My PC Run It?.
Specific enclosure recommendations and prices: TBD.