Say you’re buying a laptop, desktop, monitor or GPU. What video ports should you look for?
Here’s a list:
- HDMI 2.1 supports 7K, but there are no monitors or laptops with this port yet.
- DisplayPort 1.4 and Thunderbolt 3 both support 5K, which is 5120 x 2880.
- DisplayPort 1.2 supports 4096 x 2304, also called DCI 4K. If you have a USB-C port that doesn’t support Thunderbolt, this is also its maximum resolution.
- HDMI 2.0 supports 4096 x 2160.
Tons of disclaimers apply.
First, these are maximum resolutions, not minimum. A port in a specific device may support a lower resolution than this. This may be because the GPU doesn’t support this resolution, or there’s insufficient internal bandwidth between the GPU and the port in a laptop. Another problem is that some standards bodies let manufacturers claim that they support a particular version of a protocol even if they don’t support all its features.
Second, don’t go by GPU specs: just because a GPU supports a particular resolution, and the laptop you’re considering buying uses that GPU doesn’t mean that the laptop will support the full resolution.
Third, you need the right cable to make use of the full resolution of a port. Using an older cable, or the wrong cable, will result in a lower resolution.
Fourth, I’m not considering dual cable setups, like the Dell 8K monitor, which requires two DisplayPort cables. This is an annoying hack not worth investing the huge amount of money for.
Fifth, this also works with alternate modes. When we say that DisplayPort 1.4 supports 5K, it doesn’t means that your laptop has to have a physical DisplayPort. It can have a Thunderbolt 3 port that supports DisplayPort alternate mode. This means that when you plug a DisplayPort monitor into such a port, it switches to speaking the DisplayPort protocol. The monitor thinks it’s connected to a DisplayPort port. As long as both sides support DisplayPort 1.4, you get whatever benefits it offers, no matter the physical connector . USB-C can support DisplayPort and HDMI alternate modes, and DisplayPorts can support a HDMI alternate mode.
Sixth, this also works with protocols that are carried on top of other protocols like Thunderbolt. If a DisplayPort 1.4 data stream is encapsulated within Thunderbolt , you still get the benefits of DisplayPort 1.4, like 5k support.
Seventh, DisplayPort also comes in a mini size, and HDMI in a micro size. These shouldn’t affect the resolution.
Eighth, I’m assuming you’ve connected a single monitor. For example, the 2018 Macbook Air supports one 5K monitor, but not if you’ve connected a second monitor .
Ninth, I’m assuming you’re using right ports. Some Macbook Pros have more bandwidth to the ports on the left side than the right, though they’re all Thunderbolt 3.
Tenth, this is assuming 60 FPS, which is what computers use. If you want a higher frame rate, like for VR or gaming, the maximum supported resolution drops. Conversely, if you’re playing a movie on a TV, you don’t need 60FPS, so you can increase the resolution to UHD when you otherwise can’t.
Eleventh, this is assuming 8 bits per channel (red, green and blue). Some HDR displays support 10 bits per channel, which reduces resolution.
Twelfth, this is without chroma subsampling or other types of lossy compression that degrade the signal.
Thirteenth, we’re not even considering aspects other than resolution like wide color, number of audio channels, support for high-bandwidth devices like webcams and external hard discs, carrying power from the monitor to charge the laptop, etc. This post is complex enough already.
What you should do
So what should you do? Buy devices that have maximum compatibility, by supporting all the above protocols: DisplayPort 1.4, HDMI 2.0, USB-C and Thunderbolt 3. This goes for both monitors and computers.
For example, I wouldn’t buy the LG UltraFine monitors, because they work only with Macs.
If you’re buying a 5k monitor, insist on having both DisplayPort 1.4 and Thunderbolt 3 support. That way, you can use it with, for example, the 2016 Macbook Pro, which doesn’t support DisplayPort 1.4. Or with a PC GPU that supports DisplayPort 1.4 but not Thunderbolt 3. These are two different standards for 5K resolution, and you want your monitor to support both, to be compatible with any computer. Likewise, you would want your computer to support both, so that it’s compatible with any monitor. I would also want a 5k monitor to support HDMI 2.0 at 4K resolution, upscaled to 5K.
 Keep in mind that two laptops (even if they’re both Macbook Pros) with Thunderbolt 3 can support DisplayPort alternate mode, but different versions. The 2018 Macbook Pro 15-inch supports DisplayPort 1.4. But other Macbook Pros, support only DisplayPort 1.2. So if you were to plug such a laptop into a 5K monitor’s DisplayPort 1.4 input, it wouldn’t work at 5K resolution.
 The Macbook Pro can tunnel DisplayPort on top of Thunderbolt 3. This is not an alternate mode, because alternate mode stops speaking the Thunderbolt 3 or USB-C protocols. The practical effect of this is that alternate mode requires support on only one side, while tunneling requires support on both. As a concrete example, the LG UltraFine 4K monitor speaks only the USB-C protocol, receiving DisplayPort carried within it. It doesn’t speak native DisplayPort, so if you were plug it into such a port, it wouldn’t work.
Sometimes, two data streams are tunneled. For example, the 2016 Macbook Pro supports a 5K monitor, but it supports only DisplayPort 1.2, which doesn’t support 5K. How, then, does it support 5K? By carrying two DisplayPort 1.2 streams. The monitor pretends it’s two monitors with half the resolution each, and displays one stream on one half.
 If you have two monitors, connect them to two different ports rather than daisy-chaining, which means connecting the second monitor to the first. This forces both monitors to share the bandwidth of one port.