How do dual Graphics cards work?

so what is the second card (or the one on slot 1) actually doing?

It turns out that the stuff a graphics card has been doing all this time is almost exactly what we used to call an Array Transform processor. It can, in parallel, execute the same set of mathematical instructions (like multiply and accumulate) in lock-step, on thousands of numbers at a time. There are some really interesting problems that could use that kind of compute power.

So.. the second card is doing ... computation.

The trouble with having a graphics card doing massively parallel computations is that it gets interrupted to re-draw the screen 60 to 100 times a second, and it can't just pick up where it left off. So the second card is deliberately NOT connected to any displays, so it does not get interrupted by trivial stuff.

what is the second card (or the one on slot 1) actually doing?

Nothing, except when you run one of the few OpenCL-enabled applications.

It probably is best when talking apps that use an installer and moving to different hardware to do a clean fresh installs.

Until such apps are updated which can be long 2 yr product cycles, they won't leverage the nMP configuration and Dxxx AMDs.

Odd in some ways as SLI and CrossFire have had a long history of assisting graphics. Or even GPGPU and CUDA (a lot of tears were shed when it became clear CUDA was left out)

Have you discovered and read

http://www.macperformanceguide.com

has a lot of tips and help and test results. And yes the Dxxx do have problems.

Maybe Yosemite will help. Maybe the next generation nMP.

Maybe Adobe.

The "oMP" like the 2012 5,1 suddenly were worth more and could use two of your choice GPUs or GTX 7xx.

http://www.barefeats.com has done a lot of testing always worth checking in your research.

If you are in the first 14 days after purchase you should be able to return it.

Your iMac could have GTX in the high-end model. And doesn't have the problems.

SSD speed is not a strict requirement. You can use a Source Drive and a Destination drive, both different from the Boot drive, to good effect for most projects.

RAID is NOT faster if you use it for both Source and Destination. A RAID gets its speed from overlapping EITHER Reads from multiple drives or Writes to multiple drives for one very large file. Random Reads and Writes, or references to more than one file at a time are slower on a RAID.

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There are also some external SSD drives, USB-3 as well as ThunderBolt.

On the late 2013 Mac Pro, although there are four USB ports, there is only enough bandwidth to run one USB-3 full duplex at full capacity. So one or two USB-3 drives is fine, but for time-critical production stuff NOT more than a few USB-3 drives for that model Mac Pro.

This is the correct answer. The Dual GPU configuration remains nearly useless well over a year after the machines were announced and about a year after they were released. This is partly Apple's fault for doing almost nothing substantial with the drivers or OpenCL's kit and documentation since announcing these machines, and partly because a lot of developers who said they were on board in the run-up to the Mac Pro's release, balked or were just full of it.

Not really a question of dev cycles either as at the very least many developers might show a "sneak peak" or let users know through their social media that they're still "working on it". Nope. Not a word from any of them. The most I've seen are comments like "we're still exploring how to take advantage of this machine" or "we are planning something but there's not timetable" (loosely translated as "no time soon"). Except Adobe, for which the words were "sorry bro, we didn't support that", altough to be fair the CC2014 release was WAY too close to the Mac Pro's release to do much about it. By the time January of last year rolled around, the entire suite was a finished product (no new features would've been added from that point). However I wouldn't hold your collective breath for CC 2015. Odds of strong GPGPU support being added for the idle card are about 100:1 IMO.

Apple did work on Final Cut Pro -X to make it take good advantage of the second graphics card on the new Mac Pro. Everybody else (especially Adobe) not bloody much.

Grant Bennet-Alder wrote:

Apple did work on Final Cut Pro -X to make it take good advantage of the second graphics card on the new Mac Pro. Everybody else (especially Adobe) not bloody much.

Which has been Adobe's approach to the Mac OS segment of their market for quite some time. The days when they were a company I respected are long gone.

checked with other software developers before installing graphics cards that no one else seem interested in

I see the world somewhat differently.

For certain sectors, the leader was NVIDIA. Its CUDA technology is proprietary. But NVIDIA has not been good about providing proper support or internal details about how their chips and CUDA actually work. So if Apple signs on with NVIDIA, Apple is betting the entire high end on stuff that NVIDIA controls, and NVIDIA does not have a very good track record regarding support and internal workings. For Apple, that is not a tolerable situation.

So Apple said instead, Apple is backing OpenCL, which is still young, but will run on any Graphics card, not only NVIDIA. Apple then produces Final Cut Pro -X to show how it can work, and says they stand ready to help developers re-tool to use this Open Standard.

Users may currently feel they are caught in the middle, with Apple saying Open Standard and few developers committing support. But computer History is littered with dead companies that said, "Do it my (proprietary) way, and no licensing or participation by anyone else".

I will say Apple did a nice job of showing what these cards can do by optimizing Final Cut for it, but it makes it all the more frustrating because that's it. There's nothing else in the professional space (please no Pixelmator comments anyone) that does anything remotely similar with this machine. So far. I haven't given up all hope but I'm getting there.

Either way Apple has dropped the ball on the drivers and API fronts, which for developers is where the rubber meets the road. Instead of making it easy for people to adapt their wares to this machine, Apple has left OpenCL migration a difficult process (which it always was -- and that's part of the reason Adobe never went wild with OpenCL, just adding support for it here and there).