[JIML] Thunderbolt PCIe Speed Limitations v.6.x

This chapter discusses the maximum PCIe bandwidth available for transferring uncompressed video data over Thunderbolt on macOS systems.

Thunderbolt 3 provides an aggregate bandwidth of approximately 2750 MB/s, considering overhead and shared resources. However, when dealing with uncompressed video data, specific factors such as resolution, colour depth, and frame rate play a crucial role in determining bandwidth requirements. For example, a 1080p resolution video at 60 fps with 10-bit colour depth and YUV 4:2:2 format typically require around 248.8 MB/s. Due to Thunderbolt 3's shared bus and inherent overhead, the actual maximum PCIe bandwidth available for transmitting uncompressed video data may be lower than the overall Thunderbolt 3 bandwidth, possibly approaching the estimated requirement.

Precise calculations are challenging due to system-specific variables. Therefore, we highly recommend contacting us when planning multichannel capture systems based on Mac Minis and/or Mac Studios. A general recommendation is to distribute channels over different Thunderbolt ports.

Below you can find a table with reference values, tested with a new Mac Mini (M1 and M2), a Sonnet Echo Express III, and a Blackmagic Design DeckLink Quad 2.

*Given the hardware configuration employed for this test, the available number of SDI inputs was limited to eight (8).

The provided table presents a comparison between the anticipated channels that should be feasible ("Channels (calculated)") and the verified channels that are actually achievable ("Channels (tested)"). It is important to note that the calculated Thunderbolt bandwidth for PCIe and the actual achievable bandwidth may show variations, which necessitate appropriate testing. We aim to provide you with comprehensive information. If you have any specific concerns or inquiries, please do not hesitate to reach out to us. Your satisfaction is our priority, and we are here to address any queries you may have.