Back in the bad old days of computing, when the need for graphics was minor, there were basically two choices - either you had a CGA card capable of 320x240 pixels, or an EGA that managed 640x480 with a massive 16 colors or even 256 colors.

Macs traditionally had higher resolutions, although the highest at the time where black & white, grayscale at best. If you got color, it would be designed for a 13 inch monitor, but often at thousands or millions of colors.

Today, we are all familiar with, and most computers are capable of, a wide range of different resolutions if you have the right monitor.