A computer monitor is a screen which displays information. Technically the monitor is the whole assembly including the screen, the circuitry that drives it, and sometimes the stand or mounting that holds it up.
It’s not unusual for a computer to be connected to more than one monitor.
Monitors are usually either built-in (such as on laptops, or machines where the screen and processor is in the same unit) or receive the data to display via a video cable.
Monitors typically require their own power supply too, which is provided by a separate power cable.
Note that monitors often have their own “on/off” button, so if the screen is blank, check that it’s switched on (as well as the computer it’s connected to).
Pixels and resolution
The monitor screen is comprised of tightly-packed dots, arranged in a grid, whose colours can be individually set. These dots are called pixels and are usually implemented as tiny liquid crystals in front of a backlit light-emitting diode (LED) screen. The number (or, more accurately, the density) of those pixels is the display’s resolution.
High-resolution screens whose pixels are too small to be individually distinguished by the human eye are called retina displays.
Aspect ratio & orientation
The relative dimensions of the display — the width:height ratio — is its aspect ratio. This is independent of the resolution. There are different ratios available but 16:9 is common. It’s also possible to get ultra-wide screens.
Most monitors are viewed in landscape orientation, which means the display is wider than it is tall. Portrait orientation is taller than it is wide.
The monitor refreshes its display many times a second. The frequency at which it does so is its refresh rate. Most computer monitors aim to “paint” the whole screen up to 60 times a second (this is considerably faster than earlier TV or cinema technology). Refreshing the screen display requires that the monitor determines the precise colour for every single pixel. Calculating this is an intensive task (especially if there are millions of pixels), which is why today’s monitors have their own dedicated graphics processing units (GPUs).
There are a number of different types of video cable. If you need to connect a computer to a monitor, you need to know what kind of connectors each has in order to choose a cable that will work between them.
Computers without monitors?
Monitors are an essential component for desktop or laptop computers. But not all computers need them all the time: remote servers (such as as webservers) that spend all their time responding to requests from other computers, or embedded devices operate without them. Examples include robotic controllers, the SIM in your phone, an engine management system, or the chip on a credit card.
Applications that usually have graphical output but which are deliberately being run without displaying it are sometimes called headless. For example, running a headless web browser can be useful if you want the result of what that browser does — typically as part of some other process, such as a test suite — without needing to see its output.