Digital Video Standards
There are three digital video standards in common use in PCs today: DVI, HDMI and Display Port (DP). What is less commonly realised is how many versions of each of these three standards exist. Unfortunately many devices do not make it clear which version they support, which can be important if one wishes 4K at 60Hz, or even 2560x1440 at 60Hz.
|Standard||Introduced||Max res @60Hz||Audio?|
(Where 2560x1600 is supported, the rarer 2880x1620 might also be.)
So "4K" at 60Hz requires a minimum of DP 1.2 or HDMI 2.0.
Support for more than 8 bits of depth per channel exists in DVI-DL (optional, rarely present, and never in -SL), HDMI from 1.3, and all versions of Display Port. Using more than 8 bits per channel reduces the maximum resolution at any given refresh rate, so, for instance, HDMI 2.1 is needed for 10 bits per channel and 4K at 60Hz.
This uses an annoyingly large plug, fails to carry audio, and the standard has not changed since 1999. One reason that the plug is large is that there are effectively up to three video signals present. One is an optional analogue "VGA" signal, about which no more need be said, save that, if present, a DVI to VGA adapter is trivial, with no electronics required. One is the DVI-SL signal. The final is the optional extra link to make "dual link" DVI, DVI-DL.
Not all video cards support the second link, not all DVI leads have the extra pins and wires, and not all monitors support it.
Unlike HDMI and DP, there is no standardised "mini" or "micro" connector.
HDMI was originally designed for TVs, not computers, hence the inclusion of audio and the poor resolution.
The video signal of HDMI up to 1.2 is highly compatible with DVI-SL, and converters need no electronics. But for resolutions beyond 1920x1200 HDMI raises its transmission clock beyond 165MHz, and becomes incompatible with DVI.
Unfortunately the ports and cables look identical for all current versions of HDMI, yet to achieve higher resolutions than 1920x1200 sender, receiver and cable must all support the higher clock rates.
HDMI cables may be marked as "standard" (1.0-1.2), "high speed" (1.3-1.4b), "premium high speed" (2.0-2.0b) and "ultra high speed" (2.1).
DisplayPort is the newest standard, and has always supported 2560x1600@60Hz. Like HDMI, it comes in multiple versions, and it can be hard to discover which a particular video card, cable and display really support.
DisplayPort would not be compatible with HDMI or DVI, save that many (but not all) DisplayPort devices are designed to switch to the HDMI standard if an HDMI/DVI device is detected. Such ports may be marked "DP++", and the protocol works for transmitters (video cards) but not receivers (monitors). Passive adapters require that the monitor accept a 3.3V signal when a 5.0V one would have been expected, else active adapters which boost the voltage may be used.
DisplayPort, from version 1.2, can support multiple monitors daisy-chained on a single output.
In the Real World
Far too many devices state HDMI, DP or DVI without specifying which version they support, and surprisingly many do not support standards released years before they were first manufactured.
I am writing this using a Iiyama ProLite XB3070WQS monitor. It was manufactured in 2014, and has a native resolution of 2560x1600 and DVI, HDMI and DP digital inputs. However, only the DVI and DP inputs support 2560x1600. The HDMI one is HDMI 1.2 only, and, worse, the modes the monitor advertises stop at 1920x1080, which has a 16:9 aspect ratio, and do not include 1920x1200, which has the 16:10 aspect ratio of the screen. A 1920x1200 HDMI signal is accepted, but nothing will select it automatically.
I have an XFX R7 240 graphics card (which I don't use). It offers HDMI 1.4a, but only DVI-SL and no DP. Like the monitor, it dates from about 2014, and whilst it supports 2560x1600@60Hz, it does not support it in any form compatible with the monitor.
I also own a Radeon RX550. Whilst it does support DVI-DL, the AMDGPU driver for Linux fails to recognise this, and treats it as single link. Fortunately it has DP too, so can drive my monitor at 2560x1600 directly. Its sockets are in the above photograph, which gives no hint that the HDMI output is HDMI 2.0.
But in practice I tend to use a Radeon HD6570 from 2011, which supports 2560x1600 fine over its DVI-DL interface.
Even Intel CPUs with embedded graphics lag behind the standards. A desire to run a 3840x2160 monitor at 60Hz is not unreasonable, and needs HDMI 2.0 as standardised in 2013. However, an Intel Core i7-8086K, launched in 2018 and the top of its range at the time, supports HDMI 1.4, not 2.0, and will drive 4K monitors at 60Hz over DisplayPort only. At the time of writing (August 2020) I am not away of any desktop Intel CPU with HDMI 2.0 support. However, AMD has supported it since at least 2018 (Ryzen 3 2200 G).