Output device
An output device is any piece of computer hardware equipment which converts information into a human-perceptible form or, historically, into a physical machine-readable form for use with other non-computerized equipment. It can be text, graphics, tactile, audio, or video. Examples include monitors, printers, speakers, headphones, projectors, GPS devices, optical mark readers, and braille readers. 

In the industrial setting, output devices also include "printers" for paper tape and punched cards, especially where the tape or cards are subsequently used to control industrial equipment, such as an industrial loom with electrical robotics which is not fully computerized.

Monitors 

A display device is the most common form of output device. It presents output visually on computer screen. The output appears temporarily on the screen and can easily altered or erased, it is sometimes referred to as soft copy also. The display device for a desktop PC is called monitor.

With all-in-one PCs, notebook computers, hand held PCs and other devices; the term display screen is used for the display device. The display devices are also used in home entertainment systems, mobile systems, cameras and video games.

Display devices form images by illuminating a desired configuration of pixels. Raster display devices are organized in the form of a 2-dimensional matrix with rows and columns.

Headless operation 
A computer can still function without an output device, as is commonly done with servers, where the primary interaction is typically over a data network. A number of protocols exist over serial ports or LAN cables to determine operational status, and to gain control over low-level configuration from a remote location without having a local display device. If the server is configured with a video output, it is often possible to connect a temporary display device for maintenance or administration purposes while the server continues to operate normally; sometimes several servers are multiplexed to a single display device though a KVM switch or equivalent.

Types of display (monitor) 
There are 2 types of monitors, they are Monochrome & Colored Monitors. Monochrome monitors actually display two colors, one for the foreground and one for the background. The colors can be black and white, green and black, or amber and black. The Colored Monitor is a display device capable of displaying many colors. The Color monitors can display anywhere from 16 to over 1 million different colors.

Monochrome display 
A monochrome monitor is a type of CRT computer display which was very common in the early days of computing, from the 1960s through the 1980s, before color monitors became popular. The most important component in the monitor is the picture tube. CRT basically means cathode ray tube. The CRT use cathode-ray-tube technology to display images, so they are large, bulky and heavy like conventional or old televisions, because old televisions also used the CRT technology only to display the television films or television images. To form the image on the screen, an electronic gun sealed inside a large glass tube fires electrons at phosphorous coated screen to light up the appropriate pixels in the appropriate color to display images. The phosphors glow only for a limited period of time after the exposure of the electrons, the monitor image must be redrawn/refreshed on a continual basis. Typical refreshment rates are between 60 and 85 times in a second.

They are still widely used in applications such as computerized cash register systems. Green screen was the common name for a monochrome monitor using a green "P1" phosphor screen.

Colored display 
The color monitors are sometimes called RGB monitors, because they accept three separate signals (red, green, and blue). In contrast, a monochrome monitor can display only two colors one for the background and one for the foreground. Color monitors implement the RGB color model by using three different phosphors that appear red, green, and blue when activated. By placing the phosphors directly next to each other, and activating them with different intensities, color monitors can create an unlimited number of colors. In practice, however, the real number of colors that any monitor can display is controlled by the video adapter.

Monitor displays types include:
 CRT display monitors
 TFT (Thin-film transistor),
 flat panel
 LCD (Liquid Crystal Display)
 OLED
 LED

See also 
 Input Device
 CPU

References