Dual Layer Media

[edsmith77]

Having been mainly a lurker and reader and not wanting to wait for my question to be discussed, I thought I'd post a question similiar to the subject topic that happened in a different thread.
I think, I understand the process of mass producing single layer discs. But then maybe not, I believe that I have read here that they are mainly pressed. Now is this the same type of process for mass producing d/l disks or do companies use large banks of recorders to burn d/l discs in a 24x7 operation?
Lastly, is there a way or tool to use that will tell whether a d/l is +/-. If there is such a thing as - d/l. I am only asking about the commerically produced versions and not the blank ones you and I can purchase over the counter.

[Gen-An]

All commercial DVDs (single and dual layer) are pressed, not burned, and they all read as DVD-ROM.

[edsmith77]

Gen-An,
Thanks. Still a bit confused. If dual layers are pressed, then I presume they just glue [ } the layers together and cover them both with some protective covering.?
Also, then in that case they are neither + or - ?

[aanaravs]

This should help: https://www.videohelp.com/forum/viewtopic.php?t=199925