Three types of ports are commonly found on the back of a desktop monitor today: HDMI, found on almost every computer; DisplayPort, used by graphics cards in desktop PCs; and USB-C, which carries video, audio, data, and power over a single cable.
The choice between the three depends on two things: what the computer provides as an output, and what you want to display. A high resolution combined with a high refresh rate requires more bandwidth than Full HD office use, and not all ports support the same levels.
What a Video Port Carries
A video port carries an image and, in most cases, audio. Its limit is defined by two figures: resolution, meaning the number of pixels displayed, and refresh rate, meaning the number of images displayed per second. The combination of the two determines the bandwidth the connection must support.
Bandwidth depends on two elements, both of which matter equally: the version of the port, on both the computer and monitor sides, and the cable. An older cable connected to a newer port brings the whole connection down to the cable's level. This is the first thing to check when a monitor refuses to display its advertised resolution.
Three families of digital ports are used across monitors sold today: HDMI, DisplayPort, and USB-C. VGA and DVI remain as two older families that can still be found on existing equipment. A desktop monitor may carry several of them at once, allowing two computers to remain connected and letting you switch between them through the monitor's menu.
The Laptop Case
A laptop rarely offers all three ports. Compact models often have only USB-C, while thicker models retain HDMI, with DisplayPort then provided through a docking station. The first thing to check is therefore what the computer outputs, not what the monitor accepts.
A laptop's USB-C port does not always carry video: this capability is called DisplayPort Alternate Mode, and the manufacturer specifies it in the computer's technical specifications, sometimes with a logo next to the port. Without it, the same cable will only carry data and power.
For a second monitor, there are two options. Connect each monitor to a separate video output on the computer. Or use a docking station, or a monitor that relays the signal, when the laptop has only one usable video output.
HDMI, the Port Found on Every Type of Computer
HDMI is found on laptops, desktop PCs, game consoles, set-top boxes, and televisions. It is the lowest common denominator: when you do not know what the other device provides, there is a good chance it has HDMI.
Its version determines what it can support. A typical 4K desktop monitor may offer HDMI 2.0, supporting 3840 x 2160 pixels at 60 Hz, which is suitable for office use and video playback. HDMI also carries audio, allowing sound to be sent to the monitor's speakers or headphone jack.
DisplayPort, the Port for Desktop PCs
DisplayPort comes from the world of computing, whereas HDMI originated in the world of video. Graphics cards in desktop PCs almost always have DisplayPort, often several, as do professional laptop docking stations.
At a comparable version, it supports bandwidth at least equivalent to HDMI and natively supports daisy-chaining multiple monitors from a single output on compatible systems. On a two-monitor desktop setup, it is the port to favor when the graphics card provides enough outputs.
USB-C, Video and Power over a Single Cable
USB-C changes the nature of the connection. The same cable carries video, audio, data from peripherals connected to the monitor, and power to recharge the laptop. A computer placed on the desk can therefore be connected with a single cable and leave the desk charged.
This connection requires two conditions. The computer's USB-C output must support video mode, which not all USB-C ports do. And the power delivered by the monitor must cover the computer's requirements: JAPANNEXT desktop monitors equipped with charging provide 65 W, such as the 27-inch WQHD IPS monitor with USB-C. The details of this charging, its power levels, and its limitations are covered in our article on the USB-C monitor with Power Delivery.
VGA and DVI, What Remains of the Older Ports
VGA is a 15-pin analog port, recognizable by its trapezoidal shape and two screws. It does not carry audio and loses sharpness as resolution increases. It can still be found on meeting-room projectors and older equipment.
DVI is digital and wider, with two mounting screws as well. It does not carry audio either. These two ports are mainly encountered in existing computer fleets, where they may require an adapter. An adapter adds another link in the chain, and therefore another potential limitation to check.
The Monitor's USB Ports and Keyboard Sharing
A desktop monitor often has USB ports whose purpose is not immediately obvious. The two USB-A ports can be used to connect a keyboard, mouse, or USB drive directly to the monitor. A square USB-B port sends these peripherals back to the computer, turning the monitor into a hub on the desk.
This is the cabling that makes the KVM function possible, for keyboard, video, and mouse. Two computers connected to the same monitor can share a single keyboard and mouse, allowing you to switch between them without unplugging anything. A headphone jack generally completes the setup, providing audio output for headphones or speakers.
When the Monitor Stays Black, Check the Port First
A connected monitor that displays nothing is most often caused by the connection rather than the computer. Four points should be checked in order, from the most common to the least common.
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The input selected on the monitor. A monitor with multiple inputs displays the one selected in its menu, and automatic switching is not always enabled.
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The cable. A cable designed for a lower resolution may produce a degraded or unstable image, or no image at all.
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The adapter direction. An adapter from one port to another does not always work in both directions: the adapter's specifications indicate which direction it supports.
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The USB-C video mode. A USB-C port that does not carry video can provide power and transfer data without ever displaying an image.
Reading the Connectivity Section of a Product Specification
The technical specifications list the ports and, for the main ones, what they support. The 27-inch 4K UHD monitor with USB-C, reference JN-IPS27UHDR-C65W-HSP-W, for example, specifies HDMI 2.0 at 3840 x 2160 and 60 Hz, USB-C 3.1 at 3840 x 2160 and 60 Hz, DisplayPort, two USB-A 2.0 ports, USB-B, and a headphone jack. Three cables are included with the monitor: HDMI, USB-C, and USB-A to USB-B for the hub.
Three checks are enough before ordering. Does the computer have the intended port as a video output? Do the resolution and refresh rate supported by that port cover what the monitor displays? Does the included cable match the chosen port, or will you need to provide one? The panel type can then be checked as well, since it determines the image itself, a point covered in our comparison of IPS and VA panels.
