OS X 10.3.8 will work on any Mac that has built-in USB. That includes every iMac and every Power Mac from the B&W G3 on. The OS X system, itself, makes use of the Altavec features of the G4, so the Sonnet upgrade will make even more of a difference with OS X than it did with OS 9. You friend's son should get the OS X version of Sonnet's cache enabling software to take advantage of the L2 & L3 cache on the upgrade card. <http://www.sonnettech.com/downloads/osx_upgrade_sw.html> On Mar 1, 2005, at 5:19 PM, revDAVE wrote: > Passing this on from a friend... > > My son has a G3 Blue & White with a Sonnet Encore G4 500 Megahertz > upgrade. > Will System 10.3.8 work on this computer?