On the topic of software "compatibility," I am curious if it has more to do with copy protection and the differences between floppy drive mechanisms than it does with 64k vs 128k ROMs. For truly, some copy protected floppies would only work properly when used in the internal 400k drive -- they wouldn't work right in an external 400k drive. I think SmoothTalker 1.0 was like that. That implies such copy protected 400k floppies may not work well or at all in an 800k drive.