Hoe do games tell apart original discs from fake ones?

[TheGateKeeper]

I have been wondering this ever since I was a kid. You know how if you copy the contents of a disc onto another disc, and put it in your computer the game will not read it and won't start up (for games having CD checks at startup).

When I was a kid I used to think it was the image on the disc surface, but it probably isn't that.

What is really the thing they use to tell them apart?

[Slay]

A film that is placed over the blank side of the disk.
That stop people from being able to pirate them, however some game developers don't do it, just gewgle the stuff.

[TheGateKeeper]

A film that is placed over the blank side of the disk.
That stop people from being able to pirate them, however some game developers don't do it, just gewgle the stuff.

Thanks! I suspected it was something like that.