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Can the GeForce Drive two 30" at Full Rez?
- Thread starter Brent Turbo
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Tenton's post has some stong information, and is exactly the kind of answer I was looking for. The picture of the dual monitor computer didn't do much for me, because it's a picture of a surfer and a mountain, and would be the perfect type of images to show if you wanted to hide what resolution your screens were showing.
I was never suggesting some sort of huge cover-up, I just know that when you're pumping up a new product, it doesn't make wise marketing sense to say "it's great, but not quite as great when you add the second monitor." So you'd wanna word it funny to get around that point. Apple is a corporation, and that's what corporations do.
But from what I've read, particularly Tenton's information, it seems logical enough that they can, in fact, run full resolution in a dual monitor configuration. I'm a little concerned at how personally some took this discussion, however. I wanted to be clear on the specs, and being skeptical is never a bad thing, right? I do not trust large corporations' marketing, no matter how friendly their products are!
I was never suggesting some sort of huge cover-up, I just know that when you're pumping up a new product, it doesn't make wise marketing sense to say "it's great, but not quite as great when you add the second monitor." So you'd wanna word it funny to get around that point. Apple is a corporation, and that's what corporations do.
But from what I've read, particularly Tenton's information, it seems logical enough that they can, in fact, run full resolution in a dual monitor configuration. I'm a little concerned at how personally some took this discussion, however. I wanted to be clear on the specs, and being skeptical is never a bad thing, right? I do not trust large corporations' marketing, no matter how friendly their products are!
I know this discussion has been settled elsewhere but for anyone who's just now getting around to reading this thread (like myself)...tenton said:
Tenton, your math doesn't add up.
1920 x 1080 x 60 Hz = 124,416,000 That's 124 MHz, no? Also:
2048 x 1536 x 60 Hz = 188,743,680
Now, the 30" resolution is:
2560 x 1600 x 60 Hz = 245,760,000 (~246 MHz)
Dual DVI: 2 x 165 MHz = 330 MHz
Sorry if I'm repeting a lot of what other people have said. I just want to set the math straight.
The FINAL solution...
Holy crap. Brent, I commend you. You're taking alot of flak for simply stating an interperetation. Has anyone actually called apple yet? I'm sure they'd be able to answer a simple question like "Does the 6800 support dual 30" displays at full resolution?" with a yes or no. Give it a try.
Holy crap. Brent, I commend you. You're taking alot of flak for simply stating an interperetation. Has anyone actually called apple yet? I'm sure they'd be able to answer a simple question like "Does the 6800 support dual 30" displays at full resolution?" with a yes or no. Give it a try.
dongmin said:
It's not my math; those numbers are quoted from the Digital Display Working Group link that Brent gave earlier. There's got to be a reason for it; I'm just not sure what it is. I've been in the market for a 1920x1200 display (unfortunately the Apple Cinema Display is out->no TV inputs, no sale) and people have had issues with those resolution monitors, with cards that don't support the reduced blanking frames (or with that option off). My guess is that other things that need to be sent aren't counted (which include those blanking frames, which aren't part of the refresh rate) with the the raw multiplication of the pixels and the refresh rate.
Edit: In reading over the DVI 1.0 spec (available for free at the ddwg website linked below), my guess was correct. The fourth factor missing from the calculation is termed "Bandwidth Overhead (loosely defined as blanking)."
The page is at http://www.ddwg.org/dvi.html (DDWG is the group that developed DVI, IIRC).
How the hell did this get posted in "Macrumors.com News Discussion", only "MacRumors" is supposed to be able to post here 
edesignuk said:How the hell did this get posted in "Macrumors.com News Discussion", only "MacRumors" is supposed to be able to post here
i thought that, but felt to dumb to ask....anyone???
2560 * 1600 = 4096000
4096000 = 4.1 million = 30" at max resolution
4096000 * 2 = 8192000 = 8.2 million = two 30" at max resolution
WWDC slide with two 30" displays, "8 Million pixles!"
The new GeForce card runs both displays at full resolution. Done Deal
4096000 = 4.1 million = 30" at max resolution
4096000 * 2 = 8192000 = 8.2 million = two 30" at max resolution
WWDC slide with two 30" displays, "8 Million pixles!"
The new GeForce card runs both displays at full resolution. Done Deal
edesignuk said:How the hell did this get posted in "Macrumors.com News Discussion", only "MacRumors" is supposed to be able to post here
It got broken off because of the level of activity on this one particular misconception.
And thanks for the picture of "Dual Dual Link." We kinda all agreed on that on page one...
I *did* ask someone from Apple, who says that none of his Apple contacts know for sure if it can drive both screens at full rez, and that it's been a bit of a discussion even within Apple. He did confirm that the 30" display has one video connector (not two, as I had previously been informed), and in order to achieve full resolution even on ONE screen, the refresh rate takes a hit (due to the Dual Link DVI standard and its inherent limitations), therefore the framerate drops well below 60fps.
If anyone has the 23" Cinema Display, you'll notice the same method was used to achieve its full rez through the single link DVI interface, which does not natively support the resolution of the 23" display. It has a lower than 60hz refresh rate, and therefore has a maximum framerate somewhere in the low 50s.
Again, to clarify, the maximum resolution for a Dual Link DVI port is 2048x1536 @ 60 Hz. In order the increase the resolution output from a Dual Link DVI port (to 2560x1600), the refresh rate must drop, and hense the framerate. So it looks like two displays can crank out full rez at once, but regardless of the number of displays, the frame rate must take a hit at full rez. This is now confirmed.
Apple doesn't know? That's very un apple-like. I don't suppose we'll get anywhere with this debate if even the people behind the products can't figure it out themselves. Why don't we all just wait until august and find out, aye?
pdpfilms said:
I think it's pretty much been narrowed down to two possibilities by now:
1) Card can drive 2 30" displays at full resolution. DVI Dual Link standards remain intact, and high resolution is achieved by increasing the blanking interval and decreasing the refresh rate of each display (same would have to be true with single display, as well), same as Apple did on the 23" Cinema Display to make it standards compliant with Single Link DVI.
2) Card can drive 2 30" displays at full resolution. DVI Dual Link standards have been modified by Apple. 30" Display is only compatible with 6800 Ultra DDL card, and 6800 Ultra DDL card is only compatible with the 30" display. In order the bend the standards, this would have to be a 100% proprietary setup.
My vote is on #1, because that's what Apple has done before, to remain VESA compliant, and it just makes sense. Only a hardcore gamer would notice a FPS drop from 60fps to 45-50fps, and I don't think these are marketed at hardcore gamers.
pdpfilms said:
Heh, I was about to say the same. Credit for Brent for not going postal when having to restate the same point over and over..
Steve clearly stated the "8 million pixels with two monitors" point, so he's clearly convinced the max resolution can be supported on just one port. Maybe he just meant it will work "within a year"..... <cough!>
whooleytoo said:Heh, I was about to say the same. Credit for Brent for not going postal when having to restate the same point over and over..
Steve clearly stated the "8 million pixels with two monitors" point, so he's clearly convinced the max resolution can be supported on just one port. Maybe he just meant it will work "within a year"..... <cough!>
Thanks, man. At least someone noticed that I've been saying the same thing over and over again, but people just don't get it. Two "Dual"s in a row ain't that hard to get your mind around.
Looks like hypothesis #1 from my post above is the winner. I've been doing a lot of research on the DVI standard, and it's fully possible to exceed the stated resolution of the Dual Link DVI specification by implementing an increased blanking interval. The same trick Apple used to get their 23" HD display to work on a Single Link connection, which does not support its native resolution in theory, but can be juiced into working by using a higher blanking interval.
Now a real DVI expert would have to step in and answer this, but I'm not sure if an increased blanking interval decreases frame rate, or results in drop frames, or none of the above. I tend to understand that it's a reduced frame rate, since the Cinema Display 23" HD's refresh rate drops to 52Hz when in 1920x1200 mode.
So yeah, two 30" displays at once guys. Full resolution. Higher blanking interval (regardless of single or dual display configuration) at 2560x1600 mode. That looks like the final answer. Thanks to those to actually helped find the answers here. Thanks for the frustration of having to repeat that I know that it's "DUAL Dual Link" like 900 times.
pdpfilms said:
Just an FYI "pdpfilms", Brent didn't "simply state an interpretation". He was trying to come across as though he knew a fact, in other words, he made an accusatory statement.
Here's a part of the original post:
"On order to support the full 2560 x 1600 resolution, the monitor must utilize BOTH ports in tandem on the nVidia 6800 card. It is possible to run two 30" displays off of one card, but they must both run at a lower resolution, as supported by DVI standards.
In short, you cannot have two 30" Apple displays running at 2560 x 1600 on the same computer."
Sounds like more of an accusation based on misinformation to me. Not at all a simple question.
Nice job on this, Brent. You got a lot of replies from people who didn't bother to actually understand what you were asking but were able to work it out with the help of a few who actually contributed.
As far as blanking intervals/refresh rate, I think the issue lies between a nominal refresh rate and an actual refresh rate. As others calculations have shown, the refresh rate of the 30" display falls within the 330 Mhz (2*165 Mhz) limit of dual dvi. So it would seem that the standard blanking interval for a crt running 60hz lowers the actual refresh rate from 330 Mhz to something below the 246 Mhz someone calculated for the 30" displays. Increasing the interval between blanking signals will bring the maximum actual refresh rate to something above 246 Mhz but below 330 Mhz. At least, according to my theory.
As far as blanking intervals/refresh rate, I think the issue lies between a nominal refresh rate and an actual refresh rate. As others calculations have shown, the refresh rate of the 30" display falls within the 330 Mhz (2*165 Mhz) limit of dual dvi. So it would seem that the standard blanking interval for a crt running 60hz lowers the actual refresh rate from 330 Mhz to something below the 246 Mhz someone calculated for the 30" displays. Increasing the interval between blanking signals will bring the maximum actual refresh rate to something above 246 Mhz but below 330 Mhz. At least, according to my theory.
MacQuest said:
It's a computer monitor, man. Get on with your life! We all learned a little something. My original thoughts on the monitor were wrong. Who cares? I'm certainly not losing any sleep about it, and I can safely say I know enough about DVI standards now to carry on the world's most boring conversation, should it ever arise. It's a no lose situation, if you ask me!
Hehe, more pointless info. I'm not too knowledgeable about blanking rates and such, but with a little calculation I've discovered that a 2:1 ratio between data cycles and blanking cycles would generate a data refresh rate of 220 Mhz, which is above the 188 Mhz display rate of dual dvi's max. resolution. Upping that ratio to 4:1 would give a data refresh rate of 264 Mhz, which is above the rate calculated for the 30" display. so there are the numbers to prove it. ha. (if I'm understanding all this properly.)
Brent Turbo said:
I don't [actually didn't] really care about the displays at first, I was upset with your false claims. Just because you don't understand something or believe it to be different, doesn't give you the right to go making false accusations [you did blame Apple's marketing afterall] and claiming them as fact.
Brent Turbo said:
Yes we did. As I stated above, I didn't care about all the technical aspects at first but it's cool to know and understand them now.
Brent Turbo said:
Bingo!
Brent Turbo said:
Not me anymore. This should be a lesson to a) know what you're talking about when you post, or b) ask a question if you're not sure instead of claiming falsities.
Now get me off of this emotional rollercoaster... I got a headache!
Kyle? said:
Damn! That's some hardcore research. It all makes so little sense, and combined with the fact that, barring a lottery winning, none of us are ever going to hook up a pair of these things to a G5 anyway, I'm ready to devote my brain to other topics. Thanks for the info, and the understanding!
MacQuest said:Not me anymore. This should be a lesson to a) know what you're talking about when you post, or b) ask a question if you're not sure instead of claiming falsities.
Now get me off of this emotional rollercoaster... I got a headache!
Actually, I've learned to tread lightly when discussing politics, religion, and Macintosh!
Scratching my head
Here's a quick recap on DVI throughputs.
Single-link DVI: maximum pixel rate: 165MHz to 225MHz -- i.e. 165megapixels/sec to 225 megapixels/sec -- depending on the particular transceiver chip pairs used and physical link characteristics.
Let's consider the Apple 23" Cinema Display: resolution=1920*1200
Assume the horizontal blanking period of 7% (ballpark figure that depends on the particular LCD display's design)
To display 1920 pixels horizontally, you'd thus need to send 1920*1.07 pixels i.e. 2054 pixels
Assume the vertical blanking period is 12% (again, a ballpark figure. I don't have the exact specs for Apple's displays)
To display 1200 rows vertically, you'd need to send 1200*1.12=1344 lines
With a 165 megapixel per second budget, you could thus achieve a refresh rate of:
165000000 / ( 2054 * 1344 ) ~= 60Hz.
There is thus no need for Apple to resort to shenanigans like "overclocking out of spec" a DVI link to support a 23" display.
Let's now consider Apple's latest 30" display at 2560*1600.
Again, assume a 8% horizontal blanking period and a 12% vertical blanking period.
Total virtual pixels to be sent to display: 2560*1.08*1600*1.12=4954522
Pixel budget via a single dual-link DVI connector: 2*165 megapixels/sec = 330 megapixels/sec
Achievable refresh rate (ballpark estimate):
330000000/4954522 ~= 67Hz
The calculations are TRIVIAL for somebody who knows e.g. what "165MHz" means.
There's thus NO REASON at all to surmise that Apple must artificially lower the refresh rate for its 30" display, or suggest that a two-connector NVIDIA 6800 card can't possibly drive two 30" displays at their full 2560x1600 resolutions and at decent refresh rates.
Blanking periods
"Blanking" periods were a necessity for Cathode Ray Tube-based display units, as the electrical potential necessary to return the electron ray to its start position once a phosphor line was scanned took a certain amount of time to be established in the driving coils.
LCD displays, obviously, don't use inductance coils and high-voltage electrical fields to drive an electron ray to paint a picture, and thus don't really require large horizontal or vertical blanking intervals.
LCD display's blanking periods are a relic of the past and are mainly maintained for compatiblity reasons, e.g. to unify timing generators for video cards that can drive DVI and analog VGA displays, and give some time to software to access the frame buffer for glitchless redraws squeezed in the vertical blanking interval.
Here's a quick recap on DVI throughputs.
Single-link DVI: maximum pixel rate: 165MHz to 225MHz -- i.e. 165megapixels/sec to 225 megapixels/sec -- depending on the particular transceiver chip pairs used and physical link characteristics.
Let's consider the Apple 23" Cinema Display: resolution=1920*1200
Assume the horizontal blanking period of 7% (ballpark figure that depends on the particular LCD display's design)
To display 1920 pixels horizontally, you'd thus need to send 1920*1.07 pixels i.e. 2054 pixels
Assume the vertical blanking period is 12% (again, a ballpark figure. I don't have the exact specs for Apple's displays)
To display 1200 rows vertically, you'd need to send 1200*1.12=1344 lines
With a 165 megapixel per second budget, you could thus achieve a refresh rate of:
165000000 / ( 2054 * 1344 ) ~= 60Hz.
There is thus no need for Apple to resort to shenanigans like "overclocking out of spec" a DVI link to support a 23" display.
Let's now consider Apple's latest 30" display at 2560*1600.
Again, assume a 8% horizontal blanking period and a 12% vertical blanking period.
Total virtual pixels to be sent to display: 2560*1.08*1600*1.12=4954522
Pixel budget via a single dual-link DVI connector: 2*165 megapixels/sec = 330 megapixels/sec
Achievable refresh rate (ballpark estimate):
330000000/4954522 ~= 67Hz
The calculations are TRIVIAL for somebody who knows e.g. what "165MHz" means.
There's thus NO REASON at all to surmise that Apple must artificially lower the refresh rate for its 30" display, or suggest that a two-connector NVIDIA 6800 card can't possibly drive two 30" displays at their full 2560x1600 resolutions and at decent refresh rates.
Blanking periods
"Blanking" periods were a necessity for Cathode Ray Tube-based display units, as the electrical potential necessary to return the electron ray to its start position once a phosphor line was scanned took a certain amount of time to be established in the driving coils.
LCD displays, obviously, don't use inductance coils and high-voltage electrical fields to drive an electron ray to paint a picture, and thus don't really require large horizontal or vertical blanking intervals.
LCD display's blanking periods are a relic of the past and are mainly maintained for compatiblity reasons, e.g. to unify timing generators for video cards that can drive DVI and analog VGA displays, and give some time to software to access the frame buffer for glitchless redraws squeezed in the vertical blanking interval.
WinX said:
You are correct in this. In fact, in reading the DVI spec from DDWG, they even refer to the blanking with the words "artificially high" and the expectations (of the DDWG group) was for the blanking intervals to be reduced or eliminated from being sent through the data cable.
Let me clarify the point I made earlier. Apple (and other video card and monitor makers) are using the blanking intervals (which are artificially high for LCD monitors) to send image info. Not lowering the refresh rate. Turning down the refresh rate is one way to get around the raw 165 Mhz limit; reducing the blanking intervals (which seem to be higher than the percentages that WinX is using in his calculations) is the other. (some video cards and monitors that don't support a reduced blanking interval obviously would require you to turn down the refresh rate or use the VGA cable for the really high resolutions).
If I'm reading things correct, the 165 Mhz (or 330 Mhz for dual link) limit is a copper wire limit for DVI.