At the start of the 1st level on legendary right after landing, heading strait down the hill side looking towards the big gate. If you watch closely you will see a invisible Elite waking from the flaming warthog past the gate and past the Moa and will disappear completely right before the front door of the empty house. If killed will drop a plasma repeater and a computer notepad of some sort. 343 industries what is that Elite for, what does that pad mean and does it have any other in game or external links.
The pads are for added extra to the game. Basically they add a little more depth to the game for those people who are more interested in the story of halo then just playing the game. There are many of these pads around the campaign and there are some that only show up on legendary difficulty. Hope that answers your question.
They are reffered to as Data pads and are scattered throughout the game’s campaign, providing the player with an more in depth information on the story of reach. Some can only be found on specific difficulties, just like Rawrgasm xXx said.
Specifically, there are two data pads on each level. One can be found on any difficulty. The other is found only when playing Legendary and usually only in the presence of one or more difficult foes (Gold Ranger Elites as I recall).