Paul wrote on 12th Jan. 2015 04:39 UTC + 2 :
Hello,
A long time ago, I read a book, I do not remember whether it was about
MS-DOS or about assembly programming (I think it was MS-DOS), that
presented the basics about a different formatting for a floppy disk,
introduced as a way of some sort of cryptography, so that the floppy can
only be read with the intended software. Easy to imagine a transposition
to a CD, and then a DVD.