color graphics adapter (CGA)
The CGA card (Color Graphics Adapter) was the first text graphics card for personal computers. In addition to the text mode with 80 characters per line with 25 lines and 16 displayable colors, the CGA card had three graphics modes that could be programmed on a pixel-by-pixel basis.
The first mode allowed display of eight colors at various intensities. The second mode has four colors at a resolution of 320 x 200 pixels, and the third has only two colors at a resolution of 640 x 400 pixels. This results in an aspect ratio of 16:10.
The low values were due to the high cost of the memory chips.