Question about emulation

When you think about a drive, you think to a huge room with a lot of shelves. Each shelf have a fixed number of slots .. Each shelf have an identifier (a number) .. And you can easily find your books given the shelf number and slot number (you can translate this example in a lot of different ways .. If you know what is LBA, shelf# is LBA block#, slot# is the position inside your block).
Since each shelf have a fixed number of slots, if you need more storage you need a room with more shelves.
But there are other options .. If your books have different "sizes" (different number of pages, different dimensions) a shelf like the one I described before may be the worst choice, since you waste a slot with either a tiny book or a huge one.
Now think different (I guess I'm quoting some ads here) .. Think to a shelf with its number (as before) but without a fixed number of slots. You put your books one close to the next one and put tiny post-it on the books to help you in searching desired book on the self.
If you want to find a specific book you still need shelf# and an additional information (third from right) to find desired book. That's what best describes (in my poor english) CKD emulation.
Thus what does "emulation" means ?? Emulation means that your storage can "emulate" different storages with different architectures, different addressing, different features .. A drive can be made out of 512bytes sectors, 520bytes sectors, or even without sectors. And your trusty DMX can emulate all of them, flawless.