This method might not always be accurate

http://www.360drives.com/list

that link gives a list from where , if you know the lot number of your 360 you can determine the drive.. now this has been done purely by experiment so there might be a few mislabelled drives and such

there is also a way to confirm by checking with the 4th to last digit of your serial number more info as well as info about the latest ixtreme mods can be found here

http://www.team-xecuter.com/forums/showthread.php?t=63164

hope i helped