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Typical resolution are 640 x 480 or 1024 x 768 pixels. The cathode ray tube if the monitor is very similar to that of a TV set. Inside the tube there is an electrons beam which scans the screen and turns on or off the pixels that make up the image. The beam begins in the top left corner, and scans the screen from left to right in a continuous sequence similar to the movement of our eyes when we read, but much faster. This sequence is repeated 50, 70 or 85 times per second, depending on the system. If the rate of this repetition is low, we can perceive a flickering, unsteady screen, which can cause eye fatigue. However, a fast-moving 75 Hz' refresh rate' eliminates this annoying flicker. What we see on the screen is created and stored in an area of RAM, so that there is a memory cell allocated to each pixel. This type of display is called bit-mapped. On monochrome monitors, bit 0 are visualized as white dots, and bits 1 as black dots. |
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