Why does emulation only work after I have played off the original CD?

[bailey]

I have a backup of Battlefield 1942 that I made and I was testing it. I installed but the game woulnd't start. I made sure that I had Safedisc emulation turned on, and tried many times and it still didn't work. Then I put the original cd in, played for a few minutes, quit, and now the backup works.

A simliar thing happend when I was testing another program that has emulation.

Why does this happen technically speaking? If I need to have the original CD in order to get the emulation started, then I am screwed if the original gets destroyed and I only have the backup?

[baadf00d]

I think it works like that so you can make an ISO that works by playing the game with the original CD with emulation enabled, then rip the ISO.

An ISO made this way would then, in theory, simply work in the future.