What is the difference between an IDE and a PCI drive?

Early G3s with Revision A ROMs do not support slave devices on their IDE controllers, limiting them to one device per bus (normally one optical drive and one hard disk). Additionally, they came with onboard ATI Rage II+ video. G3s with Revision B ROMs support slave devices on their IDE controllers, and had the onboard video upgraded to ATI Rage Pro. G3s with Revision C ROMs also support slave devices on their IDE controllers, but the most significant technical differences are the newer Open Firmware version than the previous two models (2.4 vs. 2.0f1) and another onboard video upgrade, this time to ATI Rage Pro Turbo.