Reply 20 of 44, by ripa
But, having said that, isn't it a bit curious the chosen resolution for CGA was 320x200 when this in fact could not be displayed correctly on a standard monitor (unless you had black bars that is).
320x200* can easily be displayed on a standard 4:3 CRT monitor. Think about how a CRT works: it draws horizontal lines from top to bottom and repeats. The number of lines can change without affecting the aspect ratio (less lines -> bigger gaps between lines and more lines -> the lines blur together). The horizontal resolution defines how the electron beam intensity changes within one line. 320 pixels means it can change 320 times per line. A video mode like 2000x400 can be displayed on a 4:3 CRT without black bars: there are 400 horizontal lines and each line can change intensity 2000 times.
*200 lines is too little for CRTs - the video controller actually generates two video lines from one "line" in memory. There are also hidden lines which don't take up any memory, but which are generated to allow the CRT to return the beam from the bottom right to the top left position.