darknezz19 wrote:
Read about some games, like Megaman X and Demon's Crest, that require the rom to be mirrored properly otherwise copy protection kicks in. But aren't those games 2mb in size anyway and would fill a 2mb chip completely? Could other games like say a 2.5mb or a 3mb game require to be mirrored if they were going to a 4mb chip?
Mega Man X is 12 megabits. Demon's Crest is 16 megabits. Both access ROM in a mirrored location. The reason is because on most Copier devices at the time, no mirroring would take place. This let them identify a copier was being used. Rather than outright refusing to work they hid various things to make completing the game impossible. Both games can be patched to avoid that.
Remember that these protections were not designed to stop flash carts or people using eproms. But they can trigger on a flash cartridge or when using eproms if you don't pay attention to how you are mapping memory.
I can't recall any other game besides these two that actually uses ROM mirroring as a protection. Other games use SRAM size instead since again earlier copiers always made their full SRAM available to every game loaded. This made copiers easy to detect. Again these checks were easily patched. Earthbound famously has one immediate check easily patched but other checks later in the game including one that erases all of SRAM and I believe crashes the game. Ofcourse this effect is limited on those running copiers where SRAM is likely frequently backed up on floppy disk.