• PC World
• »Peripherals
• »Monitors

Cathode ray tube monitor: an analog display that produces images by illuminating phosphors with an electron beam.

You can buy the fastest computer available, but it won't do you much good if you can't see the results. The most popular display remains the cathode ray tube monitor, which has been available for more than 70 years. CRT monitors:

• Create vivid colors and render detailed images and text.
  
  
• Cost much less than their nearest competitors, liquid crystal displays.
  
  
• Continue to evolve, with developments such as flat screens and shorter tubes.
  
  

The tube itself resembles a bottle turned on its side, with a slim neck and wide face. Inside the thin end of the tube, three "guns," each firing at a slightly different angle, emit electrons in a beam that illuminates phosphors coating the inside of the tube. Following signals sent by your PC's graphics controller, the beam sweeps quickly back and forth across the thick end of the tube.

The phosphors light up when hit with electrons, mixing red, green, and blue to create the colors you see on the screen. The point where one set of adjacent red, green, and blue phosphors meet constitutes a pixel (short for "picture element"), the smallest discernible dot in a display. Because the phosphors that make up a pixel light up only briefly, they need to be constantly refreshed, which is why the beam continually and rapidly sweeps the inside of the tube.

Precision Is Everything

Precise alignment of the electron beam is critical: A slight deviation could cause the electrons to hit the wrong phosphors, resulting in a blurry image. The electrons are aimed in two ways. First, a deflection yoke--a coil of wire that creates a magnetic field--directs the electrons toward the wide end of the tube, and causes the beam to sweep across and down the screen. The yoke with its supporting electronics is responsible for the integrity of the image you see on the screen.

Then, just before the electrons hit the phosphors, they flow through either a shadow mask or aperture grille located a fraction of an inch behind the screen, which filters out stray electrons to ensure that only the correct phosphors are hit. In a shadow mask CRT, a metal sheet riddled with holes directs the electrons to the circular phosphors. An aperture grille CRT directs the beam through slots between thin, vertical wires. In either case, the space between the holes or wires (known as "dot pitch" in shadow masks and "grille pitch" in aperture grilles), determines how detailed the image can be: In general, the smaller the pitch, the more precise the alignment of the beam, and thus the crisper the images.

The resolution of the monitor--which also acts as a gauge for the amount of detail a display offers--comes from the number of pixels and lines. For example, in a CRT monitor with a 1024-by-768 resolution, the beam lights up 1024 pixels as it passes horizontally from left to right. When it reaches the edge of the screen, it stops and moves down to the next line. The beam repeats this process until it has passed over the 768 lines of pixels on the screen. When the beam reaches the bottom, it returns to the top and begins again. A monitor with a 75Hz refresh rate completes this round-trip 75 times per second. If a CRT refreshes too slowly, you'll see a flicker, which is widely believed to lead to eyestrain.