Dreamcast Hardware revision differences?

So, anyone know the changes that were made?
I heard that some play imports via a boot disk and others dont, is that right?
Anything else?

i believe the newer ones can't read CD-R's

mines an older one so hey!

Ahh right!
Oh well, dosent affect me then!
Ive got a load of DCs at the moment and just wondered if it was worth separating old stock from new or anything?

Also, newer DC's use a different connection for the wire(from the controller port board to the main board) on the controler port.

And for some reason, newer Dreamcasts have a different kind of Fan. The older one has a metal housing/heet sink. The newer one is mostly all plastic and looks cheeper.