Whats this SCSI deal??

I was curious about the whole SCSI concept after Tweak himself told me to stay away from it. I wikipediad it to learn what it was and now im just curious what MPCs alternative to it is, and which models have it

Ok its looking like most models have it, with the exception of the 1000, 2500, and 4000. I read somewhere that you can go a different route with a card change or something like that. Truth in that statement?