Some notes on 4K monitors and connecting to them
For reasons beyond the scope of this entry, I'm probably going to build a new home machine this year, finally replacing my current vintage 2011 machine. As part of this (and part of motivating me into doing it), I'm going to persuade myself to finally get a high-resolution display, probably a 27" 4K monitor such as the Dell P2715Q. Now, I would like this hypothetical new machine to drive this hypothetical 4K+ monitor using (Intel) motherboard graphics, which means that I need a motherboard that supports 4K at 60 Hz through, well, whatever connector I should have. Which has sent me off on a quest to understand just how modern monitors connect to modern computers.
(It would be simple if all motherboard supported 4K at 60 Hz on all the various options, but they don't. Just among the modest subset I've already looked at, some motherboards do DisplayPort, some do HDMI, and some have both but not at 4K @ 60 Hz for both.)
As far as I can tell so far, the answer is 'DisplayPort 1.2' or better. If I wanted to go all the way to a 5K display at 60 Hz, I would need DisplayPort 1.3, but 5K displays appear to still be too expensive. Every 4K monitor I've looked at has DisplayPort, generally 1.2 or 1.2a. HDMI 2.0 will also do 4K at 60 Hz and some monitors have that as well.
(That 4K monitors mostly don't go past DisplayPort 1.2 is apparently not a great thing. DisplayPort allows you to daisy-chain displays but you have to stay within the total bandwidth limit, so a 4K monitor that wants to let you daisy-chain to a second 4K monitor needs at least one DP 1.3+ port. Of course you'd also need DisplayPort 1.3+ on your motherboard or graphics card.)
Adding to the momentum of DisplayPort as the right choice is that there are also converters from DisplayPort 1.2 to HDMI 2.0 (and apparently not really any that go the other way). So a motherboard with DisplayPort 1.2 and support for 4K at 60 Hz over it can be used to drive a HDMI 2.0-only monitor, if such a thing even exists (there are probably HDMI 2.0 only TVs, but I'm not interested in them).
I assume that having HDMI 2.0 on motherboards helps if you want to drive a TV, and that having both DisplayPort 1.2 and HDMI 2.0 (both with 4K at 60 Hz support) might let you drive two 4K displays if one of them has HDMI 2.0. The latter feature is not interesting to me at the moment, as one 27" display is going to take up enough desk space at home all on its own.
(As usual, searching for and comparing PC motherboards seems to be a pain in the rear. You'd think vendors would let you easily search on 'I want the following features ...', but apparently not.)