The Classic environment existed under Mac OS X until Mac OS X 10.5 and can be seen as a vital link or a "bridge" between Mac OS X and the Classic Mac OS (noticeably Mac OS 9.x).

When Mac OS X was written, it was written in such a manner than Classic Mac OS software could not be run directly under Mac OS X. The Classic environment came in at this point as an emulator to bridge the two systems. Thus, it's important to realize that without the Classic environment and a full installation of Mac OS 9.x, it's impossible to run Classic applications under Mac OS X.

See also