Mac OS 9.0.4

Mac OS 9.0.4 is the final Macintosh OS to support "Old World" Macs with no Memory Management Unit (MMU). This update was a roll-up of the custom fixes for specific hardware that were released in 9.0.2 and 9.0.3, plus other fixes to 9.0. It included FireWire 2.3.3 which fixed problems with certain DV camcorders and FireWire hard disks, and Open Transport 2.6.1 which fixed a bug that could be exploited by certain Denial of Service attacks. It also included USB 1.4.2 in the Mac OS ROM file and fixed a sound issue experienced waking from 'sleep' mode. It also included a new audio extension, Sound Manager and CD/DVD driver and fixed the Y2K problem with the Date & Time Control Panel. Feature-wise, it is the same as Mac OS 9.0.

Emulation Note
Mac OS 9.0.4 is also the last Mac OS that can run on the cross-platform PowerMacintosh emulator SheepShaver, due to SheepShaver's lack of MMU emulation.

External References
SOS Apple Notes - 9.0.4