OWC’s Larry O’Connor on the New MacPro – MacObserver

[Marcus Moore]

So everything that goes into a Cubix is sharing one 16x slot? That means you can really only add ONE heavy GPU worth of horsepower, whether it’s 1 beefy card, or several mid-range ones- right?

If that’s the case, then where is the power discrepancy between a current gen MacPro and the tower? Since the internal GPUs are presumably equivalent to 2 16x slots, and via TB2 you can use an external chassis for up to 8x cards.

I’m I nuts?

[Marcus Moore]

[Dan Stewart] “Now this one I’m prepared to bet on.. I think you’ll be more likely to upgrade your iphone.”

I dunno… the breakdown on Apple’s site makes it look very user accessible (at the very least for the RAM), and the GPU side there’s some VERY obvious screws in the design. The GPUs may not be a standard PCIe configuration, but as long as the MacPro design doesn’t change in a year, the next-gen AMD GPUs should fit- even if it’s something Apple recommends they do at a store.

I’m obviously not sure, but I don’t think the machine is as locked down as you do.

[Walter Soyka]

[Marcus Moore] “So everything that goes into a Cubix is sharing one 16x slot?”

Yes.

[Marcus Moore] “That means you can really only add ONE heavy GPU worth of horsepower, whether it’s 1 beefy card, or several mid-range ones- right?”

Not really. Remember the MacBook Air demo with Premiere running on Windows 7 in Bootcamp with an external GPU and RedRocket on Thunderbolt?

The cards don’t all need maximum bandwidth (~80 Gbps for PCIe 2.0 16x) all the time. A GPU gets frame and control data, does processing, and returns the finished frame data. It shouldn’t require much bandwidth while it’s actually processing.

A little back-of-the-napkin math suggests that 80 Gbps can accommodate 324 frames per second of 1920×1080 video, with 4 channels (Resolve’s YRGB) at 32 bpc. Bump that up to 4K, that same 16x connection can only accommodate 52 frames per second.

Of course, there’s at least some overhead and other factors I’m sure I’m not taking into consideration. I also don’t know too much about how Resolve actually works internally, especially about how it divides work across GPUs, so I may be oversimplifying or off the mark entirely.

[Marcus Moore] “If that’s the case, then where is the power discrepancy between a current gen MacPro and the tower? Since the internal GPUs are presumably equivalent to 2 16x slots, and via TB2 you can use an external chassis for up to 8x cards.”

Right now, there’s no support for Thunderbolt-based GPUs on Mac OS (except via the Thunderbolterizer hacked drivers).

If my quick math above is anywhere close, 8x should be fine for HD, but will not likely be sufficient for 4K. Multiple separate 8x controllers might work nicely.

None of these bandwidth worries are a problem at all on Windows or Linux, where you can find supported motherboards with multiple 16x slots for GPUs.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog – What I’m thinking when my workstation’s thinking
Creative Cow Forum Host: Live & Stage Events

[Marcus Moore]

Thanks for the explanation. I’ve read it thru twice now and believe i get the gist, as the amish say.

So it’s up to Apple to support external GPUs via TB. It will be interesting to see if they do, with big companies like Magma already building chassis they advertise can be switched to TB2 when it’s released.

With TB2 really just a rejiggered orientation of TB1’s data rate, I wonder what the next step for Thunderbolt is. Will it be a doubling- or is the next step to go right to the optical orientation with its 100GB/s data rate.

[Marcus Moore]

I’m wondering. What’s the use case for the HDMI 1.4 port on the MacPro?

With ACDs (Retina or not) being handled by the Thunderbolt2 ports, is the intention for the HDMI port to be used for Broadcast Monitoring? Rendering a separate Video I/O box unnecessary?

That is unless you’re using Resolve, in which case you’d still need a Blackmagic box, right?