There are a total of 13 terminals to be found in Halo 2. There is 1 available for every main mission of the game, and they look different based on the mission's location. A video and full list can be found below:
[
0:09] - Terminal 1 - Mission: Cairo Station
[
0:35] - Terminal 2 - Mission: Outskirts
[
1:09] - Terminal 3 - Mission: Metropolis
[
1:40] - Terminal 4 - Mission: The Arbiter
[
2:08] - Terminal 5 - Mission: The Oracle
[
2:33] - Terminal 6 - Mission: Delta Halo
[
3:05] - Terminal 7 - Mission: Regret
[
3:24] - Terminal 8 - Mission: Sacred Icon
[
3:51] - Terminal 9 - Mission: Quarantine Zone
[
4:37] - Terminal 10 - Mission: Gravemind
[
5:16] - Terminal 11 - Mission: Uprising
[
5:48] - Terminal 12 - Mission: High Charity
[
6:13] - Terminal 13 - Mission: The Great Journey
You will also unlock all of the following achievements: