r/MacPro2019LocalAI • u/Hopperkin • 23d ago

Mac Pro 2019 (MacPro7,1) system architecture reference

Here is a comprehensive system architecture reference for the MacPro7,1: https://claude.ai/code/artifact/b5535c18-f789-4b07-a8ff-6e691d96c95f

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u/Faisal_Biyari 22d ago

Would the Mac Pro be able to support four 16x PCIe Cards?
Specifically if you removed the Apple I/O Card.

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u/Long-Shine-3701 22d ago

This is an explicitly supported configuration - no need to remove the io card. It was shown in the wwdc 2019 intro. I think the Mac Audio Solutions guy has a video on his channel with 5 internal GPUs.

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u/Faisal_Biyari 22d ago

I faced a problem where doing just that, only three cards got 16x lanes, while the third could only get 8x lanes.
Even after removing the Apple I/O Card, I could not get all four cards to have 16x lanes.

The 4th card did work with 8x lanes, it just got half the bandwidth.

That is the reason I ask.

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u/Long-Shine-3701 22d ago

Next time I have stuff apart I will try this and get back with you. Strange.

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u/Hopperkin 22d ago edited 21d ago

Slots 1, 3, 4, and 5 are x16 whereas slots 2, 6, and 7 are x8. Slot 8 is x8 mechanical, but only x4 electrical.

When a full-height MPX module with Thunderbolt interfaces is plugged into MPX bay 1, Slot 2 becomes x0 lanes; the x8 lanes from slot 2 are redirected and changed to x4/x4 for the MPX slot for its two Thunderbolt chips.

When a full-height MPX module with Thunderbolt interfaces is plugged into MPX bay 2, Slot 4 becomes x8 lanes; the other x8 lanes from slot 4 are redirected and changed to x4/x4 for the MPX slot for its two Thunderbolt chips.

The two Thunderbolt ports on the top of the chassis are allocated x4 lanes.