OCuLink vs Thunderbolt for ePCIe

Introduction

Both enable high-speed data transfer but have significant differences in performance, compatibility, and use cases. This post explores the differences and has a take on which interface is best suited for specific applications.

I looked into it as i want an external solution for my 2016 Macbook Pro, both to test PCIe cards as well as for eGPU use.

Interface Standards

OCuLink

• Direct PCIe connectivity with minimal overhead.
• Uses SFF-8611 or SFF-8612 connectors which are more bulky.
• Supports PCIe Gen3, Gen4, and Gen5, offering raw speeds up to 64 GT/s (PCIe Gen5 x4) (depends on cable and distance).
• Most common are x1 from miniPCIe/m.2 and x4 from m.2/PCIe.
• Cales support 4 lanes each and docks may use multiple up to x16 (4 cables).
• Lower latency compared to Thunderbolt due to the lack of protocol conversion.
• Less widespread in consumer devices but common in industrial, server, and storage applications.
• Cheap PCIe cards, external docks and cables available.

Thunderbolt 3 & 4 (+USB4)

• Uses USB-C (Thunderbolt 3 and 4) and supports power delivery (up to 240W)
• Supports up to 40 Gbps bandwidth, but this is shared between PCIe, DisplayPort, and other data streams.
• Requires protocol conversion, adding latency compared to a direct PCIe connection.
• Wide compatibility with Linux, macOS and Windows devices.
• Thunderbolt 3 and 4 typically is PCIe 3.0 x4

Some OCULink hardware to look at, with prices:

x16 PCIe to 4x OCULink (4 lanes each, bifurcation required – modern AMD eg.) – 25€

x4 PCIe to x4 OCULink (4 lanes, no bifurcation) – 23€ (makes no sense vs. x16 variant)

m.2 to female OCULink (OCULink cable plugs into cable, less strain than m.2 adapters, also ideal for case mount) – 20-25$

OCULink to PCIe x16 (4 lanes) w/ SATA power – ~30$

50cm OCULink cable – 30$