All versions of Mac OS X that were made to run on PowerPC systems (with the exception of Leopard) had a Mac OS 9 emulation layer called 'Classic'. It started out on PowerPC processors but later transitioned onto Intel processors with Mac OS X Leopard (10.5) the last to natively support the PowerPC architecture and Snow Leopard (10.6) the last to support PowerPC applications on Intel-based Macs. It also adds the Dock as a place to launch applications (Not dissimilar to the underused Launcher) as well as some other features. It features a new theme called Aqua which replaces Platinum from Mac OS 8 and 9. It is based off the unix kernel and provides compatibility with X11. It is a conglomoration of NeXTSTEP, A/UX, and Mac OS 9. Mac OS X is an operating system by Apple Inc.
