Both C1 and E0 Core Stepping use the same Box Order Codes....
however , if you was to buy OEM 'E0' Q9550 chip (no box and heatsink) ,
then the Code is: AT80569PJ073N ...
and if you was to buy OEM 'C1' Q9550 chip (no box and heatsink) ,
then the Code is: EU80569PJ073N ...
:)