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Comment by pilif | Hacker News Reader

Assuming the signal is transmitted uncompressed, this would be 5120x2880x32 bits per frame, so 5120x2880x32x60 bits per seconds at 60fps.

That's 28GBit/s - more than what a single TB2 port can handle and probably also more than what a lower-to-mid range GPU is able to produce.

I hope the solution to this will neither be reducing FPS nor adding compression, so it looks like we need a new display connection standard.

Please tell me that I got my math wrong as I really, really, really want a display at this resolution for my day-to-day work.

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It probably uses Multi-Stream Transport by combining the signals from two DP 1.2 ports. Something more or less like Dual-Link DVI but using 2 ports. Regarding graphics cards performance probably only high-end graphics card from Nvidia and AMD (Quadro/FireGL) can drive a screen like this with decent performance.

For anyone else who hadn't heard of it: this is what the (never-defined) "MST" refers to in the article. I'd never heard of it: it's basically daisy-chaining, or using a USB-like hub, for DisplayPort.

24 not 32 bpp - the alpha layer is not sent to the display.

If that's right, then we've got:

  5120*2880*24*60/(1024^3): 19.77GB/s

Which might work within the 20gbps offered by TB2.

I'd bet against it. Those kind of specs are almost never reliably achieved. Besides, "DisplayPort version 1.3, which was expected to be finalized in Q2 2014, will increase overall transmission bandwidth to 32.4 Gbit/s" wikipedia

aside of what rando289 said about not reaching the theoretical maximum, you're mixing up units. You'd have to divide by (1000^3) as bits are always measured in proper SI units (1KBit = 1000 Bit).

TB does 20 GBit/s

And 5120x2880x24x60 Bits/s / (1000^3) is 21.23 GBits/s, so even in the best-case scenario (which is likely unrealistic), you wouldn't have enough bandwith over TB2.

DisplayPort 1.3 will solve the issue of course, but that doesn't help me personally much as the hardware I'm using is a 2012 retina MacBook (which I'd be theoretically willing to replace to be able to use the resolution we're talking about here) and a 2013 MacPro (which I won't replace this early), neither of which have DP 1.3 support.

Oh, I didn't know that. Let's wait for DP 1.3 then.

Apparently it supports 10 bpp input, so raise the bandwidth required by 25% for a 10bit workflow.

http://www.tftcentral.co.uk/news_archive/31.htm#dell_up2715k

A lot of 4K screens aren't at 60fps, they're at 48fps.

I wouldn't be surprised if this screen is lower than 60fps.

I looked at 4K TVs recently, and if you look through the advertising they're all 4K at 30hz (ie, totally worthless for viewing anything on) due to the limitations of HDMI 1.4.

4K at 60hz (ie, totally worthless for viewing anything on)

What's wrong with that? Sounds lovely!

looks like it was a typo, parent was edited

I'd prefer 120 hz, at least for games and UI animations.

30 Hz is bad for most PC content, but it should be fine for movies, which are mostly shot and distributed at 24 frames per second.

Mostly, yes, but the trend (set by the Hobbit movies) is heading towards higher frame rates (60 and beyond). I can imagine the connectors and graphics cards are racing to get that kind of performance at those resolutions again.

This is not true. The Hobbit demonstration showed why 24fps is superior for Hollywood storytelling and movies will likely stay that way, possibly for decades.

Some reviewers seem to have that opinion, but many, many people use the high-frame-rate-simulators on their home TVs. I've seen the first two Hobbit movies in 48 fps and wish everything was there or higher. Hell, there are projects like SVP [1] to get video smoothed on your computer. People LIKE higher frame rates.

[1] http://www.svp-team.com/

Many people have the high-frame-rate turned on by default and don't know it. That's not the same as preferring the look.

The Hobbit demonstrated that people have different opinions and react differently to change. I saw The Hobbit in both formats, and I thought that the 60 FPS presentation was vastly superior to the 24 FPS.

One movie does not make a trend.

I mainly play games rather than watching filmed content, which it seems makes my use case a little bit more sensitive than other people's.

Right, but watching a 24hz source on a 30hz screen is pretty bad - the technical term is "judder" if you want to learn more.

That depends on the screen technology. 24p looks great on plasmas. I'm pretty sure modern LCDs refresh at a multiple of 24, and can natively refresh at 24 FPS when they detect 24p content. No idea about this specific TV though.

I don't think you're very familiar with any of thisthis technology.

  24p looks great on plasmas.

We're talking about the drawbacks of a 30hz refresh rate here. There are no 30hz plasma displays. They run at more like 600hz.

  I'm pretty sure modern LCDs refresh at a multiple of 24, and can natively refresh at 24 FPS when they detect 24p content

Again, that's pretty far removed from anything we're talking about.

Yes, consumer LCDs often run at 120hz these days and yes, one reason for this is so that they can display 24p content (120 is a multiple of 24) without judder.

If Dell had managed to make the world's first 5120x2880 LCD monitor that runs at 120mhz or higher you can be sure they'd be trumpeting that fact.

I think the confusion is that I'm assuming that a 30Hz display might also be able to refresh at 24Hz. I am familiar with consumer televisions, but not with this particular TV. But I see no inherent reason why a 30Hz display cannot also refresh at 24Hz, especially when the 30Hz limitation seems to be due to the display connector's bandwidth.

I apologize for my tone! You made a totally reasonable assumption, but LCDs don't work that way.

A 120hz LCD always refreshes at 120hz, essentially[1]. But it can easily display 60hz content - it just display each frame twice in a row. Same with 30hz (display each frame four times in a row) or even 24hz (display each frame five times in a row) content.

But suppose you were, say, trying to display 119hz content on a 120hz monitor. You'd have to display the first 118 frames for one LCD refresh interval, and then display the 118th frame for two intervals, which causes judder. Or you could blend all of the frames together and simulate a 120hz source (this is "pulldown").

  But I see no inherent reason why a 30Hz display cannot also
  refresh at 24Hz, especially when the 30Hz limitation seems to 
  be due to the display connector's bandwidth.

If Dell's 5K monitor has a 120hz refresh rate, it could indeed display 24p content smoothly because, as you say, the display connector's bandwidth would be sufficient.

But Dell's 5K monitor almost certainly is a 60hz panel (else they would have trumpeted the fact that it was 120hz!) and 60hz isn't evenly divisible by 24, so you get judder or have to do pulldown.

_______ [1] nVidia's Gsync is one possible solution http://www.anandtech.com/show/7582/nvidia-gsync-review

I work all day on a 30Hz 4k tv. It works for viewing lots of text buffers.

For most 2014 TVs, it's not a limitation on the TV because they also support HDMI 2.0, but a limitation on the source.

What I don't understand is why these TVs don't have a DP input so we can use them at 60fps with modern PCs (and already on the market GPUs).

>What I don't understand is why these TVs don't have a DP input so we can use them at 60fps with modern PCs (and already on the market GPUs).

Probably because every TV maker / rebrander and their mother has both an HDMI license and the tooling setup. There's, basically, 0 cost to keep usin gHDMI. Moving to DP needs licensing and retooling.

As far as I know using DP does not require a license except for using the DP logo.

Do you consider theatre movies at 24hz "worthless"? Or is there some other difference?

One thing that comes to mind is that unless you can pull them down to 24Hz, it will really suck to watch a 24Hz movie on a 30Hz TV.

Movies rely on persistence of vision (or motion blur) to pull off the 24 FPS. I don't want motion blur in anything I use a computer for aside from games - and only then if implemented properly. I haven't seen a good implementation of that yet.

30hz is just fine for a lot of big Emacs windows and terminals!

Sony's 2014 screens all support 3840x2160/60p, HDMI 2.0. Bit laggy for mouse work though.

Dell's 5K display is 60hz, or at least most articles say so.

Could you integrate the graphics card into the moniter? Surely the bandwidth between the PCI express card and the motherboard will actually be less than the bandwidth of the cable to the display.

There are some Sony screens that do this.

But the latency will probably be huge enough to be a blocker.

Heh, you solved one problem by creating another.

It works fine if you only have 1 display, then you can run everything display side.

But now lets say you have 3 displays. Now each built in GPU has have the ability to talk to other items on the PCIe bus, not just the controller. This sounds like a blessing. The host PC would only have to upload the window contents once, then each display would send the information to each other. Simple right?

But now we have to deal with hardware latency, and cross vendor standardization. Which are largely problems then bandwidth.

I never had any problems running multiple displays on separate PCI graphics cards on my 2002 PowerMac G4, why would that be a bigger challenge now?

Each of the PCI graphics cards in your 2002 PowerMac was using a long-established standard signal (VGA) to communicate with the monitors, so there was no problem.

If you build the graphics card into the monitor, you'd need a new (non-existant) standard to pipe graphics bitmaps and draw instructions between the PC and the monitor. (Unless X is up to the task... hahah)

OR, you could just extend PCI express over cables to the monitors. Which would work (you can already buy PCI express breakout boxes) but then you have much greater latency between the card and the system, etc etc etc.

> OR, you could just extend PCI express over cables to the monitors

We already have this

http://en.wikipedia.org/wiki/Thunderbolt_(interface)

Thunderbolt combines PCI Express (PCIe) and DisplayPort (DP) into one serial signal alongside a DC connection for electric power, transmitted over one cable. Up to six peripherals may be supported by one connector through various topologies.

Not enough PCIe lanes to get enough performance for games but it should be fine for desktop applications.

Why exactly should latency be such an issue for graphics cards? If the graphics card only needs to refresh the screen every 15ms what difference would a few nano seconds make for the signal to travel down a wire? I'm guessing that reading to PCI express if already >100ns for large payloads.

You can. You can also build/buy (kickstarter project?) a PCIe brakeout box. it has been done, but it's crazy expensive for what it is. For me this was the biggest thing I loved about TB. The ability to have a laptop, but also a fast external card.

But no...

This is exactly why laptops got retina displays before desktops. Need more bandwidth? Add another twisted pair. (LVDS.)

With DisplayPort and HDMI, we have to wait for the world's least competent standards agencies to add more twisted pairs. HDMI only cares about TV, so they're useless. DisplayPort is merely very very slow.

Meanwhile, there is a 5k monitor on the market but no way to connect it to anything reliably. MST is a minor disaster. (I have the Asus 4k display. I did get it working at 60Hz, but only by intentionally triggering a bug in the Nvidia driver, which triggers another bug that makes the monitor look like one monitor instead of two. SIGH. Meanwhile, ChromeOS can't handle this correctly at all, because the Intel video driver does not have that same bug. Remember how multiple monitors never worked with Linux, and they would both appear as one big display and windows would pop up in the middle spanning both screens? They fixed the glitch. Now that's exactly what we want to happen, but all the code to support that has been deleted. SIGH.)

I've been wanting a new monitor. Ideally a large, high resolution, high refresh rate monitor. Everything I've read though has lead me to hold off for precisely that fact - interconnects are currently completely insufficient to handle that kind of data, so two of three is the best you can get. Big + 4k+ = terrible refresh rate, big + 120hz = low resolution.

Hacky solutions some models use like having the monitor pretend to be multiple monitors using multiple ports (as this Dell is apparently doing) have a number of issues AFAIK.

HDMI and TB are playing a bit of catchup, but I was under the impression DP can do it today.

Technically, in theory, yes. In practice, no - every 4K+ monitor I'm aware of using DP uses the 2-monitor hack.

http://thewirecutter.com/reviews/best-4k-monitor-doesnt-exis...

Hopefully in a year things will have caught up some.

DisplayPort 1.3 is 32Gbps

Maybe they'll use two connectors and present it as two 2560x2880 monitors?

No, they use two connectors bonded together.

That's why this monitor is intended to use 2 separate inputs. If you read the article you'd know that already.

No need for the snark. The article says "if". I don't trust that.

Considering they talked about MST during the announcement AND there's not really any other viable way to drive this display, it's a pretty safe bet it will use two inputs and MST.

The snark is because your objections are lazy, and unimportant.

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