Apple II serial cards primarily use the serial RS-232 protocol. They most often were used for communicating with printers, Modems, and less often for computer to computer data transfer. They can be programmed to interface with any number of external devices which were RS-232 compatible. Most serial cards have speed ranges starting from 110 bit/s up to 19,200 bit/s, however some can be modified to go much faster. The most popular and widely used of these cards was Apple Computer's Super Serial Card, a solid design that was often copied for maximum software compatibility of the end product.