These are very mysterious things. These is nothing you have to do special, just find them and read them (though I think all you have to do is get the alert then be redirected).

There are seven in the game, and only in three levels. When you access one it will take you to a screen of text, then an alert will pop up, and then you get taken to another text screen.

Try to start each level from the beginning.

The Ark Terminals

Terminal #1: Soon after starting, the first building will be a door on the left that leads to a corridor with the terminal.

Terminal #2: In the building where you let the vehicles across the bridge, directly behind the control panel.

Terminal #3: After defeating the Scarab and getting into the final building there will be a room with sleeping Grunts. Go through the corridor and you run into a fork in the road where you can enter the next room from either the lower or bottom door. Drop down and under the ramp is the door leading to the terminal.

The Covenant Terminals

Terminal #4: Near the first elevator in the first tower, jump across the gap to find the terminal in a dark room.

Terminal #5: In the second tower that the Arbiter cleared. It's just near the door. You will pass by this tower on your way during the Hornet segment. Clear out the enemies and make a quick stop. It's also near the Thunderstorm skull. And you can't go to the third tower and then come back; you have to get both along the way.

Same as #4, but in the third tower.

Halo Terminals

Terminal #6: In the beginning of the level, after the first cave you will see a metal surface next to a ledge. Go right and toward a beam that leads you to a big

Terminal #7: Covenant building. The final terminal is to the left.

Video Tutorial for All 7 Terminals: