Mac OS 9 is the last version of the classic Mac OS, introduced by Apple Computer on October 23, 1999.
Widely considered as the most functional and stable version of the original Mac OS, OS 9 still does not have some features common to modern operating systems, such as protected memory and pre-emptive multitasking. However, it did ship from Apple with many improvements over earlier versions, such as improved OpenTransport networking, and an upgraded search tool (Sherlock 2). Like OS 8, it features Multiple Users (University of Chicago, n.d.). Perhaps most importantly, almost all of OS 9 was written in code which was compatible with PowerPC microprocessors. Earlier versions of the Mac OS depended heavily on emulation of the older Motorola 680x0 series of processors.
Apple updated OS 9 with a series of bugfixes and minor enhancements, most notably versions 9.0.4 and 9.1, in 2000 and 2001. Another update, Mac OS 9.2, was introduced in 2002, but only to improve the functioning of the Classic environment in the new Mac OS X.
In May of 2002, at Apple's Worldwide Developers Conference in San Jose, California, Apple CEO Steve Jobs delivered a mock "funeral" for Mac OS 9 during his keynote address, dressed in black and toting a coffin. The purpose of the theatrics was to announce that Apple had stopped all development of OS 9.
Despite this, Mac OS 9 lives on as the operating system of choice on millions of existing Macintosh computers, and as of August of 2003, was even still being shipped as a stand-alone operating system (along with OS X) on the 1.25 GHz model of the Power Macintosh G4. The modern operating system and successor to OS 9—Mac OS X—still uses OS 9 to provide a compatibility layer (the so-called "classic environment") for applications and hardware that still expect to be running under OS 9. Apple has provided Carbon, a toolkit for making applications that run natively under OS X and OS 9.