Thanks guys. I should have given more info. I've got four drives already. Two 160G, a Maxtor, & a Seagate. Also, a Maxtor 120G as my primary (with OS X 10.3.9) and a Hitachi 80G. I want to replace the two smaller ones with 250G drives. I thought I had read, several times in various places, that the mirror door G4 would only "see" 137G of these larger drives unless you added an additional controller card. This was the reason for my question. Now, one more time, just so it will sink in, are you saying my Mac will let me install these big drives with nothing additional added. Thanks for your earlier responses. Ron in Memphis