Explain the raster scan monitors
The refresh process must also be performed for raster scan monitors. Most television monitors are raster scan display devices : one scan-line at a time. Raster scan systems uses a memory buffer called frame buffer (or refresh buffer) in which the intensities of the pixels are stored. Refreshing the screen is performed using the information (intensity of each pixel) stored in the frame buffer. Frame buffer can be treated as a two-dimensional array. Raster display devices read the frame buffer and activate the three phosphor dots in the triad according to the value read from the frame buffer.
The entire contents of the frame buffer should be read and the pixels should be activated appropriately at a sufficiently high rate to avoid flickering of the picture. Depending on the persistence of the phosphor coated inside the screen, the monitors require different refresh rates. In some raster display devices, a frame buffer is displayed in two passes. This kind of refreshing is called interlaced. In the first pass the odd rows are refreshed, while the even rows are refreshed in the second pass. Thus, the screen is refreshed in half the time. Though this approach does not really increase the rate of refreshing the screen, but is quite effective in reducing the flicker.