I saw your posts about the undigested plasmid and the multiple bands but I have a question. Why does the fastest band migrate further than the band produced when the plasmid is digested to completion with an enzyme that cutsonly once?

Undigested plasmid DNA is super-coiled and thus migrates faster in an electrophoretic gel. super-colied DNA generates less friction in the agarose gel matrix than does a larger "floppy" digested DNA fragment. Therefore, for the same over-all size, supercoiled DNA runs faster than open-circular or linear DNA.