eGPUs Offer Gaming Performance Boosts for Laptops, But With Significant Limitations

eGPU Functionality and Caveats

eGPUs allow laptops and gaming handhelds to utilize desktop graphics cards for improved gaming performance. These external enclosures connect to compatible devices via Thunderbolt or USB4. While they can enable weaker machines to run demanding games, several limitations exist, including slower operation compared to internal desktop installations and the additional cost of the enclosure.

Bandwidth Limitations

A primary limitation of eGPUs is the bandwidth of the connection. A Thunderbolt 4 port provides 40Gbps, with 32 Gbps allocated for PCIe data. This is significantly less than the 256 Gbps offered by a desktop PCIe 4.0 x16 slot. Although much of the GPU's work, like loading textures, occurs within the card's VRAM, the cable becomes a bottleneck when new assets are loaded or frames are sent back to the display.

Observed Performance Loss

Testing has shown that eGPUs incur performance losses. Notebookcheck found deficits between 7% and 32% for an RTX 2080 Ti eGPU compared to a desktop. PC Gamer observed an RTX 4070 Ti running approximately 25% slower over Thunderbolt than OCuLink in 1440p tests, with lower 1% lows and increased stuttering. Rendering to a laptop's internal display further exacerbates this, as finished frames must travel back through the same cable.

Impact on High-End GPUs

The performance impact is more pronounced with higher-end graphics cards. PC Gamer noted that upgrading from an RTX 4070 Ti to an RTX 4090 yielded smaller performance gains over Thunderbolt and OCuLink compared to a desktop setup. This suggests that the faster the GPU, the more its potential performance is restricted by the Thunderbolt connection, making mid-range GPUs a more practical choice for eGPU enclosures.