Is there a way I can tell if this has been upgraded (ram?)

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Can you use the Finder's "Get Info" window to change the required RAM amount for some app to more than 128K, then see if the app still launches?

You can format 800KB disks as 400KB(and MFS) disks by using some key combo whilst erasing. I'm sure someone here will remember the combo.

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As I recall, it just asks you if you want 400K or 800K when you format an 800K floppy. No secret key combo required.

I successfully made several 400K disks using my Mac Plus and normal 800K floppy media.