The higher versions of the operating systems are so written that programs designed for earlier versions can still be run. What is it called?

Explanation:-

Refers to software that runs not only on the computer for which it was designed, but also on newer and more powerful models. For example, a program designed to run on an Intel 386 microprocessor, which also runs on a Pentium, is upward compatible. Upward compatibility is important because it means you can move to a newer, larger, and more sophisticated computer without converting your data.