OS X, the most important piece of software in Apple history, turns 20 today.
Going on sale in its full, public version on March 24, 2001, Mac OS X 10.0 — code-named Cheetah, the first of many cat-themed names — transformed Apple’s operating system forever. It brought user interface enhancements that persist to this day, as well as technological advances that form the backbone of Apple’s current operating systems. In fact, OS X paved the way for today’s post-PC devices, from the iPhone and Apple Watch to HomePod and Apple TV.
While Apple eventually ditched the “OS X” branding for “macOS,” and switched from naming Mac software after big cats to California locations in 2013, Cheetah’s impact continues to be felt two decades after its introduction.