After you battle a Security Robot in sector 3, Adam tells you to go to the sector 6 data room.
Make Your Way to the Data Room
From the elevator, go right to reach the Navigation Room. Adam tells you that you can get Varia Suit data from the Data Room, but you have to avoid blue X, because they will damage you if they touch you. Blue X can be stunned with your beam. Getting the Varia Suit will make you immune to the blue X.
Go to the right to go through the Save and Recharge rooms. In the next room, kill the Eeleyes, then go to the right and go through the door on the right.
In this area, go to the bottom left. There are some rocks sticking out of the left wall. Drop a bomb between those rocks, then roll through the tunnel, take the Missile Tank, then go back through the tunnel.
Destroy the barrier with Super Missiles, then go to the right and jump up onto the ledge. Before you continue going up, go to the right wall and drop a bomb between the rocks that stick out of the wall, then roll through the tunnel. In this room, you will see an Energy Tank to the right. Drop a bomb near the top of the right wall. Depending on where you dropped the bomb, multiple tunnels might appear. You want to go through the uppermost tunnel, which is one square down from the ceiling. At the end of this tunnel, drop a bomb to reach the Energy Tank.
Return to the previous room, then go to the upper right corner of the room and go through the door there. There will be a blue X in the middle of this room, near the ceiling. Shoot the blue X to stun it, then quickly go through the door on the right. There is a blue X in the upper right corner of this room, so shoot it and go downward. Go all the way to the bottom of this area and go through the door there, watching above you in case the blue X that you stunned earlier starts to follow you.
In the next room, go to the right. There is a blue X hiding in the bottom block, so shoot the top two and go to the right. Get on the ladder on the right, then climb down until you can shoot the thin wall to the left. Shoot a hole through it and go to the left. There will be some blue Xs below you, and a blue X to the left. Shoot them to stun them, and go as far left as you can go, then go downward and go through the door at the bottom left of the area.
Stay near the door and jump up to shoot the blue X, then run to the left to Speed Boost through the wall to the left. You will grab a ladder on the left side. Aim to the right to shoot the blue Xs that come toward you. Then go down to the lower level. If you want to save the game, go through the door on the right, kill the Eeleyes, then go to the right again to reach the save room. When you are done, go to the left to return to the room with a ladder near the door.
Go to the left until you reach a door, and go through it. Take the Energy Tank in this room, then bomb the floor to the left of where the Energy Tank was. Go down the hole and roll to the right to fall below and find a new door. Go through it. Bomb the right wall to fall into the narrow space below, then roll to the left. The SA-X enters the room. If SA-X sees you, it will chase you (see the next paragraph for what to do if SA-X chases you), so stay where you are to avoid that. Stay on the left side of the tunnel to avoid taking damage from a Power Bomb. After the bomb goes off, wait until you hear the SA-X shoot an Ice Beam and leave the room (about 20 seconds after the bomb goes off). When the coast is clear, leave the tunnel, then go to the right. If you don't jump, you will fall through some Pit Blocks down below, which is fine if the SA-X is not there. Go to the left to reach the next room.
If SA-X saw you, you have to go to the right while avoiding the SA-X's ice beam (which will freeze you), and its super missiles and power bombs. In the next room, shoot the wall at the bottom left, then jump up into the tunnel and roll through to reach the next room.
If SA-X did not chase you, there will be Eeleyes flying around, and Zozoros on the ceiling. The Zozoros will fall off when you shoot them, so don't stand under them when you shoot them. Shoot the wall at the bottom left, then go to the left and jump up into the tunnel. Roll through it and go through the door on the left.
There is a Save Room to the left. In the room before the Save Room, shoot the block in the middle of the floor and go down below. There are many blue Xs hidden in blocks in this room. If you don't mind taking some damage, you can get a power up now: In the lower left corner of the room, there is a long block against the left wall, and a small block to the right of that. Shoot the small block, then go down below and shoot the lower half of the long block. A blue X will come out and damage you. After it's gone, drop a bomb in the corner against the left wall. This will open a hole in the small ledge in the corner. Get into the hole, then roll to the left to reach a new room. Kill the Zozoros on the walls and ceiling, then jump up to the tunnel at the ceiling and roll into it. Drop a couple of bombs on the far left to get a Missile Tank. Then go back to the previous room.
Stand on the block that is under the hole in the ceiling, then go toward the right. Drop a bomb so it is not going to make the upper right block disappear, but it will make a hole in the floor to the left of that block. This will allow you to reach the door without revealing any hidden blue Xs. Go through the door.
Kill the Eeleyes and go to the right to find a Living Door. Kill it with a Super Missile, then go through the door to reach the Data Room. A Core-X is somehow downloading the Varia Suit data. Don't touch it or you will get hurt. When it disappears, go through the door on the right. Jump onto the middle platform and try to go to the right. The Core-X will attack.
The only way to hurt the Mega Core-X is to hit it with charged shots. Missiles will not damage it. Avoid it as it floats around the room. You can get rid of the small things floating around it by shooting them with charged shots, but the only way to damage the Mega Core-X is to shoot its main body. After you have hit it enough times, it will turn back into a regular Core-X, which is now vulnerable to missiles. Hit it with missiles until it dies, then take the Core-X to get the Varia Suit. With the Varia Suit, you can now withstand extreme heat and extreme cold without taking damage. You can also absorb blue Xs without taking damage now. They will restore 30 units of energy, but they will eventually start running away from you if you are nearby.
Get Some Power Ups in NOC
Go through the door on the right, then go to the right and go through the door there. There are blue Xs here, but now they will restore your health if they touch you. You can go through the door on the right to find a Save Room. From the Save Room, return to the previous room.
Go up the ladder in this room, then when you reach the top, go through the door on the left.
Don't walk directly to the Missile Tank, because there is a Pit Block directly to the right of it. Jump over the square to the right of the Missile Tank to get it. You will fall through some Pit Blocks after you get the Missile Tank. Go toward the left as you fall to grab a ledge. Roll into the tunnel there, and roll to the left to enter a small cave. Shoot the middle of the ceiling here to find another Missile Tank. Roll back to the right and go to the bottom, then go through the door on the right.
Go back up the ladder. The blue Xs will run away from you at this point. At the top, go through the door on the right. Go to the right side of the room and go up the ladder, then go through the door at the top.
Kill the Owtch that slithers into the tunnel, then roll into that tunnel and go to the left side to fall through a Pit Block. Go to the upper left door of this room and go through.
Make your way up this shaft. Ignore the first door on the left, because it is just a dead end. Go upward and go through the door on the right. Keep going toward the right, killing blue Xs and Zozoros to reach the door on the right. Go through.
Don't collect the Missile Tank. Approach it slowly and it will grow wings. Destroy it with a missile, then bomb the bottom right corner of the room to open a tunnel to the right, where you can get a real Missile Tank.
Now go back to the Navigation Room. Adam tells you that the SA-X can no longer freeze you now that you have the Varia Suit. Your next objective is to go to Sector 5 (ARC) and download Ice Missile data.
Go to the left and go up the elevator, then go to the Sector 5 elevator and go down.