See also: Mac OS X 10.6 Snow Leopard (for Intel architecture only)

Yet, 99% of the time, Classic was perfectly capable of running most OS 9 apps.

However, some applications and extensions won't work under Classic. It allowed Mac OS X to run Mac OS 9 applications that weren't updated to run natively on OS X (known as carbonization based on the Carbon API). 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.

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