"Always use PCI slot No 2 when using a Mac Graphics Card such as the GTX680" But Why?

Mac Pro 2009

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Original poster
Jan 3, 2014
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So I'm starting to lean towards the GTX 680 but I was told something odd by the guy at the shop today, he says no matter what a made for mac Graphics card must be installed in slot 2, not slot 1 where the old card was. But why? I'd rather use slot 1, is there a problem with using this slot for any reason or what? (4.1 MacPro, Mavericks) The guy didn't know why but maybe someone here does? Why is it bad to useslot 1 if it was used by the default graphics card? So what's up with that?
 

ActionableMango

macrumors G3
Sep 21, 2010
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You should probably ask him why he's recommending slot 2 but then can't explain why.

Apple uses slot 1, so I'm very skeptical of this random shop guy. I am not aware of any problems with slot 1. I use slot 1, as does everyone that leaves the card in the default slot.

There are some people with fan speed issues on their graphics cards, and some of those people have the problem go away when using slot 2. But that's not enough to say everyone should use slot 2.
 

Asgorath

macrumors 68000
Mar 30, 2012
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Some people had issues with no-EFI cards in slot 1 in a MacPro3,1 as I understand it. Plugging the same card into slot 2 worked fine. I'm not sure if this is still needed for the MacPro4,1 or MacPro5,1.

No matter what, a card with an EFI on it should work in any slot. Granted, there tends to be more airflow around the card if it's in slot 2.
 

Studio K

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Feb 17, 2013
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United States
So I'm starting to lean towards the GTX 680 but I was told something odd by the guy at the shop today, he says no matter what a made for mac Graphics card must be installed in slot 2, So what's up with that?
Since GTX 680 is not really an Apple card in the same way that the 5770, 5870 cards are, then the PCI fan may exhibit some unusual fluctuations when the card is in slot 1.
For some, the fluctuations appear to be a non-issue, as they are not very dramatic and not even audible. For others, the fanspeed can be quite wild and annoying. It seems to vary for some reason. Look at this thread:

http://forums.macrumors.com/showthread.php?t=1694103

Using slot 2, as Mango says, seems to 'cure' this behavior for some people. My GTX 650 (PC card) is in slot 2 and PCI fan runs at standard 800 rpms. In slot 1 the PCI fan constantly changed speed but it was not noticable. A more powerful card may or may not produce more dramatic fluctuations.

The thing to do is install in Slot 1 and monitor the fan speeds with iStat. If the Mac Pro's PCI fan revs up like mad to the point that it is annoying, then try it in slot 2.

And please report your experiences. We'd love to know how it works out.
 

GP-SE

macrumors 6502
Feb 27, 2013
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you can use either SLOT, I prefer Slot 1, since it's double wide and won't block any other slots.

As for the PCI-E Fan and PSU fan spinning up with non-apple cards, this still happens in SLOT 2, just not as noticeable as SLOT 1. Also when using SLOT 2 sometimes the load trick to return the fans to normal won't work.

The Load trick works by loading the graphics card up after a cold boot to make the fans return to normal speeds.
I use "OpenGL Extensions Viewer" available from the Mac App Store, then hit the benchmark\test, which loads\stresses the video card, and causes the fan to return to normal speed. However doing this with a video card in SLOT 2 still won't return the fans to normal speeds, it only works if the card is installed in SLOT 1.

My suggestion, put the video card in SLOT 1.
 

ActionableMango

macrumors G3
Sep 21, 2010
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Since GTX 680 is not really an Apple card in the same way that the 5770, 5870 cards are, then the PCI fan may exhibit some unusual fluctuations when the card is in slot 1.
I believe a couple of people have reported fan speed problems with the official Apple 5770 card too.
 

ScottishCaptain

macrumors 6502a
Oct 4, 2008
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I've looked into this issue extensively.

It has to do with how the Mac Pro throttles the system fans. If you install the card into slot 1, your system fans MAY run faster due to a glitch in the SMC firmware. If you stress out the GPU sufficiently, it will force the SMC to re-evaluate the fan speeds and those speeds will then drop to normal (until you shut down your system).

This is caused by the way the Mac Pro gauges the fan speeds in response to the current the card is drawing. I believe the auxiliary power cables are only taken into consideration when the card is placed in slot 1, therefore if you place the card in slot 2- the Mac Pro effectively "ignores" the current draw through the aux power cables, and this tends to bypass the whole fan issue (but only slightly, your fans will still run a bit faster then they should- but not a lot).

So, really, there is no technical reason as to why you have to use slot 2. I'd say try slot 1 first. If your fans start behaving weirdly (you'll know because the system will definitely sound louder then normal), move the card to slot 2.

-SC
 
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Studio K

macrumors 6502
Feb 17, 2013
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this is true too, if you google search I have seen threads on the official apple discussion forums.
The 5770 was only 'officially' supported in the 5,1 Mac Pro. I am guessing that those reporting fanspeed issues were using 4,1 or 3,1 or 1,1.
 

OrangeSVTguy

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Sep 16, 2007
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I got one in slot 1, 2 and 4 lol. The one in slot 4 is a Mac OEM card and the fan will run full speed on cold boot till the apple chime/bong.

I think it had to do with the PCI fans or GPU fans running rampant.
 

flowrider

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Nov 23, 2012
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I had a 3,1 Mac Pro and now have a 5,1 machine. In the 3,1, I used a self flashed AMD HD 5870 and an Nvidia MVC flashed Gigabyte GTX 570. I used both in slot one with no issues. In my 5,1, I used the same GTX 570 and now have a MVC flashed GTX 780. Again, I use slot 1 have had no issues with either card.

Lou
 

ScottishCaptain

macrumors 6502a
Oct 4, 2008
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The 5770 was only 'officially' supported in the 5,1 Mac Pro. I am guessing that those reporting fanspeed issues were using 4,1 or 3,1 or 1,1.
The 5770 doesn't have the same accommodation in the SMC firmware that the 8800GT, 4870, and possibly 5870 do- unless I'm misinterpreting the disassembly I was digging around in a while ago.

The reason why it probably worked (or didn't) again has to do with the power consumption of the rest of the machine. Since it only required a single aux cable, there's a pretty good chance that it simply doesn't draw enough power to cause issues 90% of the time.

-SC
 

Studio K

macrumors 6502
Feb 17, 2013
361
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United States
The 5770 doesn't have the same accommodation in the SMC firmware that the 8800GT, 4870, and possibly 5870 do- unless I'm misinterpreting the disassembly I was digging around in a while ago

-SC
I just read your conclusions in your thread regarding the SMC and GTX 680. A very interesting read. I'm glad someone was able to figure all that out.
 

jenzjen

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Aug 20, 2010
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I use "OpenGL Extensions Viewer" available from the Mac App Store, then hit the benchmark\test, which loads\stresses the video card, and causes the fan to return to normal speed. However doing this with a video card in SLOT 2 still won't return the fans to normal speeds, it only works if the card is installed in SLOT 1.
"only slot 1" isn't correct, I have my card in slot 2 and the OGL trick returns the fans to normal 860/600x3/800 after the test. I could be a corner case.
 

Mac Pro 2009

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Original poster
Jan 3, 2014
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Thanks for the many responses! So if the fan runs fast, is that bad? Does this mean the graphics card will wear out faster or what? Or is it just the noise bothering people?
 

ScottishCaptain

macrumors 6502a
Oct 4, 2008
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Thanks for the many responses! So if the fan runs fast, is that bad? Does this mean the graphics card will wear out faster or what? Or is it just the noise bothering people?
It's just the noise.

We're talking about a fan that runs at 900 RPM (nominally) running at ~1350 RPM instead. That's only a difference of 450 RPM. The maximum speeds for those fans are up around 4500 RPM, so you're in no risk of burning anything out.

I personally found it very annoying, because even though the speed difference is negligible it's the difference between "I can barely hear the computer" and "There's definitely something with fans running in this room".

-SC
 

riggles

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Dec 2, 2013
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My concern was more with the PSU fan, as that seemed to go up along with the GPU fan. What is a healthy limit for the PSU fan?
 

Mac Pro 2009

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Original poster
Jan 3, 2014
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It's just the noise.

We're talking about a fan that runs at 900 RPM (nominally) running at ~1350 RPM instead. That's only a difference of 450 RPM. The maximum speeds for those fans are up around 4500 RPM, so you're in no risk of burning anything out.

I personally found it very annoying, because even though the speed difference is negligible it's the difference between "I can barely hear the computer" and "There's definitely something with fans running in this room".

-SC
Just noise then? Can anyone confirm that it does not reduce the life of the graphics card? Noise does not bother me, I listen to music when I work anyway.
 

ybz90

macrumors 6502a
Jul 10, 2009
609
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Just noise then? Can anyone confirm that it does not reduce the life of the graphics card? Noise does not bother me, I listen to music when I work anyway.
The fan isn't even on the GPU, its the computer's PCI fan. So no, it will not affect the card life, these temperatures are far from dangerous levels.

Reference the thread made by ScottishCaptain; basically, there is no reason to use any slot other than slot 1. If there is enough load, the fans will be abnormally high but upon usage with something graphically intensive, it will normalize. I just run the battle.net app (don't even need to launch a game).
 

ActionableMango

macrumors G3
Sep 21, 2010
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Just noise then? Can anyone confirm that it does not reduce the life of the graphics card? Noise does not bother me, I listen to music when I work anyway.
It's fine. In fact, there are threads full of people who purposely increase their fan speeds manually in order to obtain cooler running temperatures.
 

GraniteTheWolf

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Mar 31, 2013
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I run a PC EVGA GTX 570 superclocked vid card, unflashed. Powered by the logic board for now. Soon I will be installing a jucebox optical drive power supply and upgrading the graphics card to a 770. I keep my GPU in slot 1 where the original oem card would be.

Perhaps this is why my front PCI fan runs at 1800 rpms consistently in OSX and windows, when I have it plugged in anyways. (I keep that fan unplugged because my gpu's fan keeps its self cooled just fine. I keep the front cpu fan plugged in of course. You can manually run either or fan in the front by unplugging which fan you dont want on the front fan "sled/assembly")