difference between imac cd drive and laptop cd drive?

Hi,

I bought a laptop cd drive and put it in my powerbook 1400cs, then it does not want to boot.

When i put in the imac cdrom drive (from my imac) in my powerbook it boots.

Is there some signal line different in an official Apple CD drive? Or what else? The laptop (pc) cd drive works well on my imac...

Thanks,

Zarknl.