I totally don't keep multiple posting :​v

Anyway, described how the lock-on mechanism in Sonic & Knuckles works, since there doesn't seem to be much documentation around and I wanted to keep it in a place that's easy to check and read (i.e. not an emulator's source code):

For the record, lock-on support is actually a relatively recent phenomenon. The reason for this is that S&K will happily take Sonic 3 appended to it even if the mapper doesn't work. Indeed, the mapper is only needed with Sonic 2, and even then it still doesn't care as long as the patch ROM shows up where it should be (so we got away by concatenating all three ROMs together).

PS: it's "phenomenon", not "phenomenom"? o_o