I am new to Macs and when I bought my Imac G5 it had Tiger 10.4.11 installed on it. I bought a Leopard install disc off Ebay that I thought was a retail version but it turned out to be something called a CPU drop in dvd. It loaded just fine on my computer and I resold it thinking that it was reusable, do not want to "stiff" the new buyer, but need to know what the difference is between a retail disc and a CPU. Also does the CPU have any value or did I buy a one time shot?