Why does a 20" flat screen display have a larger screen than a 20" CRT monitor?
Answer: CRT monitors use a picture tube to produce images on the screen, while flat screen displays use liquid crystal diodes (LCDs). CRT monitors shoot electrons through a grid onto the screen, while LCD monitors are made up of diodes that simply light up at different intensities. This is why CRT monitors take up so much more space than LCD screens.
So why is a CRT screen smaller than an LCD screen that is supposedly the same size? It is because CRT displays don't use the entire tube, which prevents the edges of the screen from becoming stretched and blurry. Therefore a 20" CRT display may have a viewable area of less than 19 inches. A flat screen display, on the other hand, does not use a tube, so it should have a viewable area of exactly 20". This means a 19" LCD monitor will typically have a viewable area that is greater than a 20" CRT display. So much for accurate marketing.