Help me understand 6 TB ports vs. 3 possible 4k displays, etc.

gjarold

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Nov 14, 2007
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Can someone explain how monitor connections work ?

Background: my 2009 mac pro has 3x gt120 cards, and I have six displays running off of it. Easy.

With this system, I see that there are six thunderbolt ports, so ... I could attach six displays there, right ?

BUT, every mention of the graphics cards says "up to three 4k displays" ...

What does that mean ? Does that mean that a 4k display requires two TB connections ?

And if that is the case, doesn't that mean if I attach three primary displays at 4k, all I have left is the HDMI port, and then that's it - only four displays ?

Thanks.


EDIT: OH, and also, if 4k displays take up 2x TB, and since three displays is a very common setup, then you don't have any more TB ports, right ? So you have to choose between triple monitors or fast disk connection ?
 

JesperA

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Feb 10, 2012
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why would you think that a 4k monitor would use 2 tb ports? it will obviously just use one tb connection.
 

Nermal

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why would you think that a 4k monitor would use 2 tb ports? it will obviously just use one tb connection.
That's not obvious at all; if there are six ports and the specs say that you can connect three displays then it's completely logical to think that each display uses two ports.
 

gjarold

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Nov 14, 2007
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I have no idea, actually. So a 4k display can be driven by one TB port ?

But then what explains the "up to 3" 4k displays ? Since there are two cards, you'd think that number would be divisible by 2, right ? Either 2 4k displays or 4 4k displays ?

So that's the two questions:

1. where does "up to 3" limitation come from

2. If I plug in 3 4k displays, can I also drive 3 more regular displays ?
 

JesperA

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Feb 10, 2012
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That's not obvious at all; if there are six ports and the specs say that you can connect three displays then it's completely logical to think that each display uses two ports.
Yes, and there was 4 USB ports to so every usb peripheral need to use 2 usb ports tol with your logic? Current 4k displays from Asus and Sharp only need 1 displayport connection.
 

Yahooligan

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Aug 7, 2011
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That's not obvious at all; if there are six ports and the specs say that you can connect three displays then it's completely logical to think that each display uses two ports.
Unless you read what Intel posted...

http://blogs.intel.com/technology/2013/06/video-creation-bolts-ahead-–-intel’s-thunderbolt™-2-doubles-bandwidth-enabling-4k-video-transfer-display-2/

A single TB2.0 port can drive a 4k display, you don't need two TB2.0 ports to drive a single 4k display.
 

tuna

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Apr 11, 2010
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I think you guys are overcomplicating it. 3x 4K resolution displays is just one maximum video output profile, there will probably be others for when you don't need three 4K displays. For example, I remember back when I used to shop for graphics cards, the maximum output for a graphics card might have been listed as "1x 2560x1600 and 1x 1280x800 OR 2x 1920x1200". If you wanted to power

In this case, one maximum will be 3x 4K displays, but another maximum might end up being "2x 4K displays and 2x 2560x1600 displays".
 

ender78

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Jan 9, 2005
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It takes a lot of horsepower to drive 4K displays. The three display limit is likely a limitation of the dual video cards.
 

Dalton63841

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Nov 27, 2010
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I think you guys are overcomplicating it. 3x 4K resolution displays is just one maximum video output profile, there will probably be others for when you don't need three 4K displays. For example, I remember back when I used to shop for graphics cards, the maximum output for a graphics card might have been listed as "1x 2560x1600 and 1x 1280x800 OR 2x 1920x1200". If you wanted to power

In this case, one maximum will be 3x 4K displays, but another maximum might end up being "2x 4K displays and 2x 2560x1600 displays".
This here. It's actually quite simple. It's a sum of total graphics power. If you just have a few regular displays it can probably run about 12 of them. 1080p displays like 6 or 8 of them.

Saying it can handle 3x 4k displays is their cool way of saying, "This setup can handle pretty much everything you could want to do.
 

gjarold

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Nov 14, 2007
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It takes a lot of horsepower to drive 4K displays. The three display limit is likely a limitation of the dual video cards.
Right, that's the obvious interpretation, BUT, it makes no sense for the number to be 3.

If there are two cards, then bandwidth limitations would imply a max of 2 or a max of 4.

A max of 3 makes no sense...
 

VirtualRain

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Aug 1, 2008
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Does the Ivy Xeon being suggested for this system also have a GPU on-die?

If so, does that mean there could be 3 GPU's? (Integrated Intel + 2x AMD?)
 

ender78

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Jan 9, 2005
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Right, that's the obvious interpretation, BUT, it makes no sense for the number to be 3.

If there are two cards, then bandwidth limitations would imply a max of 2 or a max of 4.

A max of 3 makes no sense...
The GPUs will be SLId, take total horsepower of both GPUs and associated video RAM, Apple calculated that they could drive three displays. Three displays is likely on or two more than most people will need to drive. This may actually be closer to 6 displays at 2K.
 

gjarold

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Nov 14, 2007
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The GPUs will be SLId, take total horsepower of both GPUs and associated video RAM, Apple calculated that they could drive three displays. Three displays is likely on or two more than most people will need to drive. This may actually be closer to 6 displays at 2K.
Isn't triple monitor pretty much de facto standard for pro users ?

Why bother with any of this if you can do your work on a single screen ? Just get the imac, right ?

Three is, in my opinion, the *minimum* number of displays this device needs to drive...
 

ender78

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Jan 9, 2005
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Isn't triple monitor pretty much de facto standard for pro users ?

Why bother with any of this if you can do your work on a single screen ? Just get the imac, right ?

Three is, in my opinion, the *minimum* number of displays this device needs to drive...
Three 4K displays at 27"+ take a up a LOT of desk space. In the photography space, two displays is the norm.
 

ZMacintosh

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Nov 13, 2008
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well it would make sense to me that its 3 4K displays.
if there are 3 Thunderbolt Controllers then the highest/max Thunderbolt device will probably consume most of that TB port/controller.

So it'd be practically one 4k Display per controller.
leaving the other Thunderbolt ports either for devices such as a pegasus, or non-video device perhaps.
 

Stetrain

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Feb 6, 2009
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Oh, ok - so there are 6 ports, but 3 controllers.

So what happens if I plug in 3 4k displays, and 3 more lower res (2560x1600) displays ?

It's hard to say at this point since we don't have a ton of Thunderbolt 2 information yet, but I think the following scenario is fairly likely considering what we know about TB 2 and how Thunderbolt behaves on the retina Macbook Pros which have two ports:

There are 3 Thunderbolt controllers (2 ports each).

Each controller can drive two 2560x1600 displays (either daisy chained from one port or one per port). This is true of the two-ports-one-controller setup on the current retina Macbook Pros.

Each controller can drive one 4k display. I'm guessing that that is instead of the 2x 2560x1600 displays.

So 3 controllers, each can drive either 1 4k display or 2 1600p displays.

Which would let you do the following combinations:

3x 4k displays
2x 4k displays and 2x 1600p displays
1x 4k display and 4x 1600p displays
6x 1600p displays


Definitely doing a lot of speculating here but it makes the most sense to me.

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well it would make sense to me that its 3 4K displays.
if there are 3 Thunderbolt Controllers then the highest/max Thunderbolt device will probably consume most of that TB port/controller.

So it'd be practically one 4k Display per controller.
leaving the other Thunderbolt ports either for devices such as a pegasus, or non-video device perhaps.
The PCI-E channels are separate from the Displayport channels with Thunderbolt.

A 4k display will probably consume the whole Displayport channel for one controller chip (set of two ports), but would leave the PCI-E channels fully open for use for things like ports on the back of the display or other TB devices.
 

gjarold

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Nov 14, 2007
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The PCI-E channels are separate from the Displayport channels with Thunderbolt.

A 4k display will probably consume the whole Displayport channel for one controller chip (set of two ports), but would leave the PCI-E channels fully open for use for things like ports on the back of the display or other TB devices.

Ahh, interesting. Thanks.

Now, theoretically, 4x pcie (which I think is what the pcie lines in TB are) is enough to drive 1920x1200, right ?

So even if I maxed out the display portion with 3 @ 4k, I could still do some kind of pcie attached external GPU doohicky ?

Do those exist ?
 

theSeb

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Aug 10, 2010
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Yeah, he actually called them "Firewire controllers" though. I guess a slip of the tung?
Yeah, he said something along the lines of, "6 firewire 2 ports with 3 controllers. You guys that use this know it's great stuff". That was a bit embarrassing and I understand now why some of the sites initially reported 6 x FW2 ports - just blindly typing away.