I'm pretty sure it'll work in your G4. Look for your model in the "Mac Compatibility" column on the right side of the screen here: http://www.sonnettech.com/product/encore_st_duet.html If you've got an AGP Graphics model, be sure to check their link in footnote 1. -- Rich > -----Original Message----- > From: Robert Fort > > So the processor now is 667MHz i was looking at one on e bay > (processor) that is made by Sonnet Encore/ST G4 Duet 1.8GHz > Dual Processor Upgrade. > How would i find out if this will work in the G4 that I have?