Here is an interesting comparison of Cortana over the course of the 4 halo games:
PTesh adds his dulcet prepubescent tones over the top of one of the new trailers for weapons...
Try upgrading your browser to Google chrome (you wont regret it). There is probably an IE...
Datapads are hidden throughout the Reach campaign and add an extra element to the story. Like terminals in Halo 3 and audio logs in Halo ODST, they provide a side story about a mysterious A.I collective called the 'Assembly'. Now finding these can be a challenge but well worth the fun if you are into hunting for information. Sadly there is no reward for finding all of these Data Pads.
For more of an Easter Egg, and more information there is another Easter Egg post about Data Pads you should check out.
To see the location of all 19 Data Pads including the legendary ones, watch the video below.