Halo 3

Guide by Eternal from X360a.org :
Note #1: You have to wait for the "Fragment Ends" message to come on before the game registers that you've got the terminal. The only exception is Terminal #2 on the level "The Covenant," this one does not give that message. Hit the A-button to scroll through a few messages, then the terminal will turn red and a few more screens will need to be read before the "Fragment Ends" message appears.

Note #2: These can be done in any order and you do not have to finish the level. It is suggested to do them all on the same difficulty. Access the terminal, wait for the end message, then you can save and quit the level.

The Ark:

1. Start the mission and once you enter the first building take a left into another door and now you should be in a curved corridor. On the inside is a Terminal.
2. After activating the bridge to let your comrades across the gap, do a 180 and you should see it. *it does not open until you activate the bridge*
3. In the third building after defeating the scarab, kill the group of sleeping covenent, then follow the corridor downwards. Once you reach a door in front that is locked, immediately on the left there's an open door. Go through and walk straight off, then do a 180 to find a secret room. It is in there.

The Covenant:

1. When in the first tower standing on the lift, face the access panel and turn left. Jump over and it's right there.
2. Land your hornet on the second tower, walk towards the entrance but when you see the locked door, do a 180. Should be right in front of you.
3. When in the third tower standing on the lift, face the access panel and turn right. Jump over and it's right there.

Halo:

1. After reaching the end of the first cave, hug the right wall and you will see a building. Jump up onto the walkway and hang a left once inside. It's right there.

Watch and Read the Youtube video Description.

i am giving u the YouTube links that i found
but if u want me to help u get it so Send a message to " mr cr0w1ey " on XboxLive telling u need help on the terminals at halo3.

1-3 Terminals are in the ark stage
4-6 Terminals are in the coven stage
last Terminal is on the last stage- Halo (easiest terminal)

**NOTE** You read the Terminal till it goes red and then wait it will bring you to more text keep pressing A untill it says at the bottom Fragment end but not all them have this.

Terminals 1-3 are located on the mission "The Ark"

Terminals 4-6 are located on the mission "The Covenant"

Terminal 7 Located on the last mission "Halo"

Video made by Roster Teeth

A couple tips & hints before going for this achievement:

- Only obtainable on Normal, Heroic, and Legendary
- Does NOT have to be on one continuous play-through, meaning you can start on 'Halo' and get it, save and quit, then continue on to 'The Ark' or 'The Covenant'
- Just because you opened the Terminal and read the cryptic message does NOT mean you followed the achievement requirements.

============== ATTENTION!!!! ==============

When you open a terminal and read the message, go to the last page and wait until the screen glitches out and brings you to a whole new message.

This is what counts toward the achievement. If you just read the message and exit, the terminal will not count toward the achievement. So before you attempt to go ahead and do this achievement, please keep in mind you have to glitch out every terminal to get the full message! Otherwise all the time you put into this achievement will have gone to waste!

The Ark:

1. Begin the mission, as you enter the first building of the game enter the first door on the left that opens up into a curved corridor. Inside the corridor will be the first terminal.

2. When in the room to activate the bridge for your team, turn around from the control panel walk up to the second terminal.

3. After defeating the Scarab, go up the ramp to the third building. Kill the sleeping covenant, then continue downwards into a room with a single ramp. Before continuing into the second room with grunts everywhere, search under the ramp for a door. This will open up into the third terminal.

The Covenant:

1. While accessing the first tower, don't activate the lift right away. Jump onto the lift and then continue going straight and jump into a dark section with a hidden terminal.

2. When you get the Hornet, go to the first tower you encounter (it has no enemies inside). Your comrades will inform you that the tower is clear and you do not need to enter. Land your hornet on the tower and inside will be the second terminal. PLEASE NOTE: If you happen to skip this tower and go forward to kill Banshee's or any other enemy past the cliff, you will not be able to turn around and go back to the second tower!

3. While accessing the third and final tower, do exactly as you did with the first tower. Jump onto the lift, jump again into the dark section and there you will find the third terminal.

Halo:

1. Run forward into the cave, as you approach the end of the cave keep right until you see a long strip of metal. Access the small opening via the metal walkway and the last terminal is inside this area.

This achievement unlocked for me on Easy (maybe because I've beaten all of the levels on Normal - and every other difficulty - already). It took me about 45-50 minutes to get them all.

I just want to add that if you want to take a few shortcuts and get all of the Terminals the easy way, just load up the checkpoints as listed:

The Ark: Mission Start, Alpha, Bravo.
The Covenant: Mission Start, Alpha (the second two terminals are both at this checkpoint).
Halo: Mission Start.

Here is my HD Game Guide for all the Terminals and skulls in Halo 3. Since this solution is just for the terminals, make sure to check out the timestamps in the description for the video. Here they are just in case you don't want to pop it out:

Terminal # (Mission Name) - Timestamp
Terminal 1 (The Ark) - 4:18
Terminal 2 (The Ark) - 5:45
Terminal 3 (The Ark) - 6:57
Terminal 4 (The Covenant) - 8:02
Terminal 5 (The Covenant) - 8:43
Terminal 6 (The Covenant) - 10:11
Terminal 7 (Halo) - 14:04

To gain credit towards each terminal you MUST read through every page. This can be done on Easy. If playing in co-op, both players must be near the terminal. Here are the contents/requirements for each terminal:

The Ark

Terminal 1: 3 pages - red screen - blue transition - 5 pages - // FRAGMENT ENDS

Terminal 2: 4 pages - red screen - blue transition - 5 pages - // FRAGMENT ENDS

Terminal 3: 4 pages - red screen - blue transition - 6 pages - // FRAGMENT ENDS

The Covenant

Terminal 4: 3 pages - red screen - blue transition - 4 pages - // FRAGMENT ENDS

Terminal 5: 3 pages - red screen - blue transition - 1 page

Terminal 6: 3 pages - red screen - blue transition - 3 pages - // FRAGMENT ENDS

Halo

Terminal 7: 3 pages - red screen - blue transition - 6 pages