Hi, I've got a Designjet 650c that needs a memory upgrade. According to the manual it has a max. limit of 20MB. As I look online I'm coming across info. and sites that show a max. of 68MB (64 MB additional + 4 MB built-in). Is the 20 MB limit only because of the time that the plotter was manufactured? Any info on this would be greatly appreciated. If I can add 64MB, that would be awesome! Eric