The job of the output device is to bring the result of computation to the outside world. The output devices accept data in binary form from the computer, converts the coded data into human readable form, and then the converted result is displayed as output.
All computers are connected to a television like screen, called the monitor. Monitor includes the graphic card or the video adapter, which is an expansion card which sends electric signals to the monitor. The monitor is connected by a cable to the video card. A device driver uses the operating system to control the video card, to make it send the right signals to the monitor.
Cathode Ray Tube (CRT)
The first computer monitors used Cathode ray tubes (CRTs), which was the dominant technology until they were replaced by LCD monitors in the 21st Century.
The first computer monitors used cathode ray tubes (CRT). Until the early 1980s, they were known as video display terminals and were physically attached to the computer and keyboard. The monitors were monochrome, flickered and the image quality was poor. In 1981, IBM invented the Color Graphics Adapter, which could display four colors with a resolution of 320 by 200 pixels. They introduced the Enhanced Graphics Adapter in 1984, which was capable of producing 16 colors and had a resolution of 640 by 350.
CRT remained the standard for computer monitors through the 1990s. CRT technology remained dominant in the PC monitor market into the new millennium partly because it was cheaper to produce and offered viewing angles close to 180 degrees.
Liquid Crystal diaplay (LCD) Screens :
LCD screens are flat and soft. An example is the TFT screen. It contains no cathode ray tube. It produces a sharp and high resolution image.
There are multiple technologies that have been used to implement Liquid Crystal Displays (LCDs). Throughout the 1990s the primary use of LCD technology as computer monitors was in laptops where the lower power consumption, lighter weight, and smaller physical size of LCDs justified the higher price verses a CRT. Commonly, the same laptop would be offered with an assortment of display options at increasing price points (active or passive monochrome, passive color, active matrix color (TFT). As volume and manufacturing capability have improved the monochrome and passive color technologies were dropped from most product lines.
TFT is a variant of liquid crystal display (LCD) which is now the dominant technology used for computer monitors.