Replying to Xbox360 red ring question (not how to fix it on my own)

my xbox got the red ring so i'm going through all the shit to get it fixed through microsoft, and i'm just wondering....what exactly does microsoft do to my xbox to fix it? I've heard before that for them its like a 1 minute fix, but i've also heard that with most of them they just dump out the xbox, put in a new one, and ship it back.

so if anyone who has sent theirs in can help, its appreciated. I'm really just curious, so no big deal if no one knows