If you are considering buying a used PowerMac G4 MDD I would look out for the single or dual 1.25 GHz processor models or even the dual processor 1.25 GHz & 1.42 GHz FW PowerMacs which have the same MDD cases but are later models with higher specs and Firewire ports. Don’t worry to much about the hard drive size or amount of memory installed as these are easy to get hold of and relatively cheap, plus thanks to the easy to access interiors it’s really easy to add both.