Arduino Due is not listed in boards

I am new to arduino i have downloaded latest arduino ide but arduino is not lsited under board list .I have checked borads.txt in arduiono/harware dir but due is not listed.When i plug in due bord serial port is enumerated and shows arduino due programming port what is possible cause

Well since no-one has responded (no suprisingly) I just figured this out myself. You need the latest Arduino software, anything above 1.5.x In Arduino IDE, you have to select Bards Manager and install a package that includes the Arduibo Due called Arduino SAM Boards.

:) Found this info to be correct after i had gone through pages of info - this should be on the commissioning page. Thanks, my Due is now communicating with PC :)