Newest Mac Pro: Displays How will 4K be displayed? : 4K 3840x2160 UHD 4096x2550 Where as: 27-inch Apple Thunderbolt Display=2660x1440

Question

How will 4K be displayed?  :
4K 3840x2160
UHD 4096x2550
Where as:
27-inch Apple Thunderbolt Display=2660x1440

Answer 1

4k is the generic term for resolutions that have a horizontal number of pixels around 4000. The two most common resolutions are Ultra Hi-Def (UHD) and Cinema 4K (C4K). The first is 3840x2160 and is exactly four times the resolution of "Full HD", or 1080p. The second is 4096x2160 and is one of the "standard" resolutions used in digital cinema projection.
The HDMI 1.4 standard supports both of these, but only at certain refresh rates. UHD, being the consumer version, is supported at 24Hz, 25Hz, and 30Hz; C4K is only defined for 24Hz since most of the material is going to be film-sourced. (This implies that 25/30Hz will include TV material at half their original rates of 50/60Hz.) Over HDMI, all four of these timing formats run at the same clock rate (297MHz, ignoring the fractional versions). This is the highest clock used in this version of HDMI, although the standard allows up to 340MHz. (There may be PC timing formats between 297-340...)
Using generic terms, we call these modes "UHD30" to imply resolution and refresh rate, and if a TV supports UHD30 it will always support UHD24 (although it is not a rule, merely a reflection of reality). A TV can only support C4K24 in 1.4, but it doesn't have to. There are many TVs that will support UHD24 or UHD24-30, but not C4K at all. So the practical limit of HDMI 1.4 is "up to 4k30."
HDMI 2.0, which the Mac Pro does not have [yet], provides dot clocks up to 600MHz (although above 340MHz, they are all divided by 4) and allows "up to 4k60" for pixel encodings of RGB444, YCC444, and YCC422. The new standard also allows 4k50/60 to use YCC420, which sacrifices some color information (known as 'uses chroma subsampling') but allows the data to be transferred at the same rate as 4k30. While "fine" for video--since it was probably delivered over BD/DVD or streaming at YCC420 to begin with--it is not fine for you computer's output.
I just got a 4k TV because I was tired of my dual 1920x1200 DisplayPort monitors after coming from the original 30" Cinema display of 2560x1600. Specifically, I used to enjoy >1080 pixels tall. But here's the problem with the 4k TV: while it has HDMI 2.0 inputs, the MacPro has only HDMI 1.4 so the output is limited to "up to 4k30". Moving the mouse is laggy and not smooth as it would be if the display were 60Hz. Furthermore, the MacPro is not offering me a choice between UHD or C4K--both of which the TV supports--and is instead defaulting to the largest resolution of C4K. This means the refresh is only 24Hz. And that's why I'm in the forums today--to see if there's a way to get my output to be UHD, but at 30Hz.
In a couple months, several companies will be selling DP-to-HDMI2 dongles that will support 4k60. So I am holding my breath until then.
Now, to specifically and accurately answer your question: Out the current MacPro's HDMI 1.4 port, you will get the highest resolution your TV (called the Sink) will support. If your TV has C4K24, then that is what will show up. If your TV does NOT have that, but has UHD24-30, you SHOULD get UHD30. If your TV ONLY has UHD24, then that's what you will get. If you get a TV, the chances are really, really good that the panel will have 3840 pixels across and 2160 lines down. In this case, you want the Mac to output that resolution and put the TV into pixel-for-pixel mode so every input datum is mapped to a single display element. Since most displays overscan, the Full mode will expand the incoming data from 2-5% which can eliminated the crispness (and also cut off the extremes of the Desktop). Also, if you are outputting C4K (like I am) AND you have switched to P4P mode, the horizontal dimension is shrunk by 6.6%.
If any of this is unclear, just reply. But I will say that this 40" TV is really useful, and once it is running at 60Hz...bellisima!