OK, I bought what I thought would work in my PowerMac. A high density 1GB DIMM from a reputable EBay dealer. Well, the chip i got said PC2700 and I know that the PM is running PC2100, but I thought they could throttle down to system speed. So with both installed, it addresses the original PC2100 512 chip, and recognizes the other in System Profiler, but not as any speed RAM, just as "DDR". In any case it doesn't work. Well the sales people told me that Macs don't run 1GB chips, and don't accept high density chips either. They say it is "PC" RAM, is this right? How can i tell?