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Can the GeForce Drive two 30" at Full Rez?
- Thread starter Brent Turbo
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arn said:
Yes, they are. There's a misunderstanding about what Dual Link DVI is, though. There are two Dual Link DVI ports on the card. Each supports a maximum rez of 2048x1536, or both Dual Link ports can be linked (creating a quad-link, essentially), for the full 2560 x 1600 resolution.
I think Brent backed down from the "no dual dvi" port stance, but he still has a valid point wrt the res limitation. The DVI page clearly shows a lower res than Jobs is saying.
However, I'm not convinced that this is a complete summary of supported res.
However, I'm not convinced that this is a complete summary of supported res.
Brent Turbo said:
I understand your confusion, based on the DVI information sheet. However, the X800 and 6800 break the above stated barrier.
The Dual Dual 6800 will push two 30-inch displays at full resolution.
Personally, I would have thought the Apple marketing machine would have come up with less confusing terminology to describe the technology in question.
Frixo Cool said:
It is. I mean, I want to believe it, but I know what marketing tries to do, and I'd like to see a link or something that shows that this card is actually capable of pumping 2560 x 1600 out of EACH dual link port. Everything I've read about DVI, and this particular card, works against that theory, and the marketing is extremely unclear.
Brent I get what your saying.. Let's wait and see though
Apple may NOT be adhearing to the Dual DVI spec. This wouldn't be the first time. If it was spec then there would be nothing that says you couldn't run a 30" off a 9800XT. I have a feeling the ports are a bastard child of dual dvi 1.0 spec.
Apple may NOT be adhearing to the Dual DVI spec. This wouldn't be the first time. If it was spec then there would be nothing that says you couldn't run a 30" off a 9800XT. I have a feeling the ports are a bastard child of dual dvi 1.0 spec.
VeloDrax said:
Problem is Apple invents enough terms as it is for industry standards, if they want their products to be easily understood by people that work in both Mac and PC industries, its in their best interest to let people know what industry standards it works with.
Basically, I would assume this is an overclocked Dual DVI signal to hit that resolution.
It's also worth doing some math. Single DVI supports up to 1920x1080 @ 60 Hz, which is ~2.1 mp. If the Dual really does only go to 2048x1536 as per that page, that's only ~3.1 mp, not a good efficiency for the second set of pins.
2560-by-1600, and 4.1 mp seems more inline with what you'd expect for 2 single dvi connections being able to carry.
2560-by-1600, and 4.1 mp seems more inline with what you'd expect for 2 single dvi connections being able to carry.
JustAGuy said:
AFAIK, these are the people who created the DVI standard to begin with, and there is no 2.0 standard.
Look, I'm not trying to cause trouble around here, and I'll glady buzz off if that's what people want, but I want people to more clearly understand that this MAY not be what they think it is. I was excited about this too, until I noticed the marketing was confusing, and it all started to look like fine print to me.
Brent Turbo said:
Brent,
sorry about getting really frustrated with you, when you were denying there were two dual links I was getting pretty flustered when its like right there.
As far as the throughput goes, I would assume my assumption to be correct, that they can scale up the DVI frequency slighly to make their targets.
JustAGuy said:
What you are saying sounds right. Infact, if you think about it, 4-5 years ago when the standard was made, anything more than 2048 probably seamed like an ungodly number of pixels that would never be made in a monitor, so they picked a number that was a multiple of 1024 (hense two standard LCDs of the time, side by side) and put that in the standard. It probably is fully capable of driving 4.1 million pixels.
Brent Turbo said:
You're assuming the numbers given here (http://www.ddwg.org/dvi.html) are absolute Maxiumum resolutions and not just convenient examples of real-life monitors/resolutions.
arn
Some basic math
To compute the bandwidth needed for a display: horiz pixels * vert pixels * refresh rate.
Single-link DVI: 165 MHz maximum
Dual-link DVI: 330 MHz maximum
2048 * 1536 * 60Hz = 188 MHz
2560 * 1600 * 60Hz = 246 MHz
So 2560x1600 at 60Hz easily works on ONE dual-link DVI, with bandwidth to spare. Last time I checked 246 < 330.
2048 * 1536 is too much for a single-link, so it has to use dual-link. However 2048x1536@60Hz does not represent the maximum bandwidth of dual-link DVI!
To compute the bandwidth needed for a display: horiz pixels * vert pixels * refresh rate.
Single-link DVI: 165 MHz maximum
Dual-link DVI: 330 MHz maximum
2048 * 1536 * 60Hz = 188 MHz
2560 * 1600 * 60Hz = 246 MHz
So 2560x1600 at 60Hz easily works on ONE dual-link DVI, with bandwidth to spare. Last time I checked 246 < 330.
2048 * 1536 is too much for a single-link, so it has to use dual-link. However 2048x1536@60Hz does not represent the maximum bandwidth of dual-link DVI!
Brent Turbo said:
Are you joking? It has dual dual link DVI connectors.
Here is how it works:
The card has two DVI connectors.
Each connector is essentally 2 DVI connectors in one, giving it the ability to support resolutions past the 1920x1200 max of a single DVI connector.
So this card has the ability to support 1920x1200 times FOUR!
That is more that enough to support dual 30" displays at their native resolution.
If you need more proof, look at this thread:
https://forums.macrumors.com/showthread.php?s=&threadid=77501
It has pictures of a G% with Dual 30" CMDs running at native resolution.
Do not underestimate the power of this card, it is very impressive.
Lets just do some math:
2560x1600 = 4096000 (The number of pixels on 1 30" LCD)
4096000 * 32(number of bits per pixel) = 131,072,000 (bits per 30" panel")
131,072,000 / 8 (to convert to bytes) = 16,384,000
For each 30" flatpanel at 32bit color depth, you need roughly 16mb of video memory. There is no reason that any 32mb+ card couldn't drive 2 of these monitors. The only reason you need the 6800 card is because of the extra DVI pins, there is no dual dvi interface on this card. On some workstation cards there are dual dvi interfaces. On my workstation at work, the graphics card plugs into a splitter cable that has a high density connector on one end and 2 dvi ports on the other. That then plugs into my 2 17" flat panels. This card does not have that. Each 30" display only requires one DVI cable, but 2x the pins because of the extra bandwidth required. The 23" display was already close to the limit of single dvi.
2560x1600 = 4096000 (The number of pixels on 1 30" LCD)
4096000 * 32(number of bits per pixel) = 131,072,000 (bits per 30" panel")
131,072,000 / 8 (to convert to bytes) = 16,384,000
For each 30" flatpanel at 32bit color depth, you need roughly 16mb of video memory. There is no reason that any 32mb+ card couldn't drive 2 of these monitors. The only reason you need the 6800 card is because of the extra DVI pins, there is no dual dvi interface on this card. On some workstation cards there are dual dvi interfaces. On my workstation at work, the graphics card plugs into a splitter cable that has a high density connector on one end and 2 dvi ports on the other. That then plugs into my 2 17" flat panels. This card does not have that. Each 30" display only requires one DVI cable, but 2x the pins because of the extra bandwidth required. The 23" display was already close to the limit of single dvi.
3G4N said:
Fess up to what, exactly? Fess up to wanting to know if this is as good as advertised? Okay! Consider me fessed.
Up to 2048x1536 for a single display, right? Is that higher or lower than the 30" display's maximum resolution?
Thanks to those who want to help find out the truth. Personally, I don't get the animosity (fess up?), it's just a computer monitor.
Brent Turbo said:
Brent,
No manufacturer would ever advertise a card capable of running two LCDs of x type if it couldn't do it at native resolution, they know they would be sued. That and besides the fact they had dual displays on display for public viewing, we know it works.
Brent Turbo said:
A single dual link DVI port on the GeForce 6800 (and there are two of these ports on the card) can drive a 30" at its native res of 2560x1600. There is only one DVI port used per 30" screen. There are other very high resolution displays that indeed connect to two physical ports on a videocard, but this is not how the Apple 30" Cinema functions.
This is a picture of a single G5 with a GeForce 6800 driving dual 30" displays.
blakespot
Answers to some of Brent's questions
There seems to be some confusion on the max resolution settings, in regards to DVI.
What Brent is linking is correct:
Dual Link = 2x165 MHz (2048x1536 at 60 Hz), Single Link DVI = 165 MHz (1920x1080 at 60 Hz).
However, there is something missing. Realize that the 23" LCD panels are 1920x1200 native resolution. This can be driven by a single link DVI port (Cinema Display HD does it, as well as most of the other 23" LCD monitors). How? There are two methods. One is, of course, to turn down the refresh rate. This isn't as bad as it sounds; LCDs don't have to paint the screen every second with information (and thus, don't need to refresh as constantly as a CRT).
The other method, which Apple definitely employs with the 23" (and probably will with the 30"), as well as many video card manufacturers (including ATi and Nvidia; my 9800 AIW has the option), is to utilize some of the blanking (syncing) frames that are normally sent (not really needed for a LCD display) as actual data frames (frames with graphic info). For those with Wintel boxes, check to see if you have an option that reads "Reduce blanking intervals for digital connections" or something like that (I'm not near my home PC to check what it says for ATi cards).
Hopefully that clears up some confusion.
There seems to be some confusion on the max resolution settings, in regards to DVI.
What Brent is linking is correct:
Dual Link = 2x165 MHz (2048x1536 at 60 Hz), Single Link DVI = 165 MHz (1920x1080 at 60 Hz).
However, there is something missing. Realize that the 23" LCD panels are 1920x1200 native resolution. This can be driven by a single link DVI port (Cinema Display HD does it, as well as most of the other 23" LCD monitors). How? There are two methods. One is, of course, to turn down the refresh rate. This isn't as bad as it sounds; LCDs don't have to paint the screen every second with information (and thus, don't need to refresh as constantly as a CRT).
The other method, which Apple definitely employs with the 23" (and probably will with the 30"), as well as many video card manufacturers (including ATi and Nvidia; my 9800 AIW has the option), is to utilize some of the blanking (syncing) frames that are normally sent (not really needed for a LCD display) as actual data frames (frames with graphic info). For those with Wintel boxes, check to see if you have an option that reads "Reduce blanking intervals for digital connections" or something like that (I'm not near my home PC to check what it says for ATi cards).
Hopefully that clears up some confusion.