How can I re-assign graphics cards for OpenGL rendering?

Short answer... you really can't.

The best you can do is ensure the 4870 is in the bottom slot with the full 16x power and the GT is in the upper slot with 8x power.

The Mac OS is flawed when dealing with multiple, non-matching, video cards. It's not smart enough to separate the two and will often get confused sending the wrong commands to the wrong card resulting often in application instability.

Which 3D apps? Are they NVIDIA specific or OpenGL agnostic?

If you pull the 120 from the system do they work with the ATI?

I'm interested in hearing your report - I was thinking of getting the 5870 and leaving the 120 in for CUDA only applications, but now maybe not!

It's my understanding that any two cards will be much slower, even if matched. It has to do with graphics memory mapping or something I don't remember right now. We use ProPresenter (from Renewed Vision) at my church and they have specific guidance against running multiple displays across video cards. It's presentation software used to do text and graphics over motion video so it's pretty video intense. Unless the display on the secondary card is simple - no video, 3D, etc. - "text only" - basically web browsing and such.

I suspect that's why most of the new cards support three or more monitors on a single card. I think the 5770 supports three monitors, I know the 5870 does - but it's over twice the cost. Our employee purchase discount is the same as education which makes the 5770 $225 - pretty appealing upgrade from my 120 for Aperture! I just checked and yup, the 5770 supports three monitors like the 5870.

I would have the 120 as a CUDA only, not with a monitor plugged into it. I bet if you had two 4870's installed you would see the same slow down. Indeed, this is probably why SLI setups in PC's have extra cables directly between the two cards - I suspect PCI Express, even with dual 16 lane slots, simply doesn't have the bandwidth to talk between the video cards and the CPU at the same time.

Message was edited by: Eric Eskam

I've run 3 displays for a number of years.

Started with 2 displays and a G5, moved to 3 with a MacPro 1,1 and 2-nVidia 7300 cards. 30" Apple and two 24" Ultrasharps. Eventually upgraded 1 card to an 8800. Stability was gone.

I had constant application crashes and system instability. It was confirmed by a couple software vendors directly, that the issue was the OS. At that time it was OS 10.4 and 10.5.

I then moved to 2-nVidia 8800s and used those for a couple years. There were occasional instability issues by far, far, less than with non-matching cards.

I've moved to an ATI5870 and 3 displays on one card this past year. The 5870 had sleep issues with the 30" and two Ultrasharps. Not huge issues, failure to wake properly or resetting resolution on the 24"s about 75-80% of the time. Annoying, but not critical. I had everything connected as it should be with Apple Dual-Link DVI adapters, but there still seemed to be that sleep issue. Once the system was awake, everything operated fine.

I've now moved to a 30" ACD, 27" Apple LED, an a 24" Ultrasharp. No issues whatsoever. Performance is great and better than I had with the two 8800 cards.

So.... I think performance with the new cards is somewhat dependent upon the actual monitor connections as well.

takeitup7 wrote:
This whole topic does make me at times envy the PC world.

Yup 😟

That's why every time I think about upgrading I start poking around and reading in these forums. Experiences of others are much better than any old reviews.

And good point about the 5870 taking up two slots 😟 Then again, if you are primarily using the card for CUDA, I doubt having the full 16 lane slot is as critical, but it's still annoying.

Also...I've heard that the 5870 is so wide physically that it prevents use of the neighboring PCI slot? True?

That depends on who is making the statement.

The first slot in the 2009 Mac Pro is double-wide slot. The 5870 takes up the ENTIRE double-wide slot.

If you have a Mac Pro 1.1, it may take up two slots.

takeitup7 wrote:
Eric I'm probably misunderstanding you...but in case I'm not...

Yup, you are - I could have probably been clearer 🙂

It's moot since the 1st slot is 16 lane and double wide - if you put a second double wide card it it blocks one of the four lane slots, so you can have two double wide 16 lane graphics cards. Powering them on the other hand....

I'll probably find out here myself - I think I am going to pull the trigger on a 5770 - with the education/employee discount i can get, at $225 it's pretty hard to resist. Then agin with the 6xxx series ATI cards out now, do I wait to see how long and how much they are, or just get the 5770 now. It's the age old question 🙂

Message was edited by: Eric Eskam