In order to prevent disk copy, the games make use of "fuzzy bits", also known as "weak bits" or "flakey bits"
Reminds me of the "weak sector" protection used on CDs, of which there was much technical information written on a few years ago; sadly a lot of that has somehow disappeared, but I managed to find one explanation of that scheme:
(The explanation there is not completely correct - the problem with more 0s than 1s or vice-versa is DC bias, since the signal from the read head is AC-coupled; here is another article that might help to explain that better: http://ixbtlabs.com/articles2/magia-chisel/ )
Reminds me of the "weak sector" protection used on CDs, of which there was much technical information written on a few years ago; sadly a lot of that has somehow disappeared, but I managed to find one explanation of that scheme:
http://web.archive.org/web/20090603002402/http://sirdavidguy...
(The explanation there is not completely correct - the problem with more 0s than 1s or vice-versa is DC bias, since the signal from the read head is AC-coupled; here is another article that might help to explain that better: http://ixbtlabs.com/articles2/magia-chisel/ )