Central Processing houses the control systems which are used to process data or experiments, archive data, and manage the CPU overhead for security and regular day-to-day operations of the entire outpost on Mars.

The level begins with the bay door opening - you see a hall ahead of you. Lock and load because its a big fight to the security bridge. Your mission is to stop Sarge.

Begin by going down the hall and boosting your health with the emergency medical station on the left (it has 80 health available). Then go down to the end of the hallway and turn left. This will trigger a timed spawn as follows: imp, 2 spiders, imp, chain gun-soldier, and 4 spiders. Walk to the opposite side (to the right of the main hall) and kill the revenant and 2 spiders. Another chain gun-soldier will spawn on the opposite side (left side), kill him, and kill the revenant. 4 more spider will emerge; kill them.

Grab the plasma canister and 30 health pack on the right side, and the adrenaline on the left side and follow the path, which will take you into the server room. Continue in, and an arch-vile will spawn, along with 2 wraiths. Kill all three. Another arch-vile will spawn with 2 wraiths. Kill them, and grab the grenades, 50 armor, adrenaline, 30 health and ammo belt from the front of the room.

Head towards the back of the room where the second arch-vile spawned. On the right side in the the corner is 30 health, and on the left side in the corner is a box of shells and ammo belt. Then go through the door and call the security bridge.

The rest of the level is set up in four areas: Central Processing (your final goal and where Sarge is), Server Bank (where you get the access key to Central Processing), CPU Bank (the area you just fought through) and Storage (an optional area that has some gear, but also some enemies).

OPTIONAL: if you want to make it through quick, you can skip to the next part. If you need ammo and health, read on. Cross the bridge, kill the 4 cacodemons, and press "Storage". Once the bridge moves, go through the door, turn right and kill the 3 whip-soldiers. Turn back to the left and go into the storage area. Grab the two ammo belts, turn around, and kill the imp. Go back to the right and go through the door. Go outside the fenced area, and grab the box of shells and the BFG cell. Then go inside the fenced area, through the door, and kill the revenant. Grab the box of shells, pack of rockets, 50 armor, 5 plasma canisters, plasma gun, 2 clips and 2 ammo belts. Go back out, kill the arch-vile and two wraiths. Go back to the bridge on on to the Server Bank. Kill the cacodemon that spawns.

NOT OPTIONAL: Once you get to the server bank, go through the door. Kill the two imps that spawn. Jump through the office window and grab the clip and rockets. Go through the door. Kill the whip-soldier, grab the 30 health. Go down the hall, turn around and kill the imp behind you. Go through the door on your left, and kill the whip soldier coming up the stairs. Go down the stairs, kill the 3 spiders and the imp. Go right, grab the clip and the shells on the desk. Kill the two spiders. Go back, past the stairs, and down the next flight of stairs. Kill the imp in the alcove to your right. Grab the 15 health pack.

Go through the door, kill the imp that spawns on your left, as well as the one that spawns down the hall. Go into the office. Grab the 2 clips and 2 plasma canisters. Go to the desk and grab the 30 health pack, and the PDA of Steve Tooloose. (Security Clearance Updated). Now we're ready to face Sarge. As you leave, you'll have to kill an imp and a wraith. Make your way back to the security bridge and press Central Processing. Kill the two cacodemons that spawn on the way.

Go through the door. Gear up on the left: a pack of rockets, 2 30 health packs, 2 clips, and 2 ammo belts. Lock and load: next room is Sarge.

Go through the next door. The room is set up as a square, surrounded by a pit. There are four columns: the one closest to you on the right has a plasma canister behind it, the one closest on the left has 30 health. The one farthest on the right has 50 armor and a plasma canister. As you fight Sarge, the bay doors on the left and right sides of the arena will open. On the right is 75 health (30, 30, 15) and on the left is armor (50 and some shards).

Sarge is a fusion of the man and a tank, and has two main weapons: the claw in his right hand (close attacks) and the BFG. To survive, you have to shoot the BFG attacks before they can detonate. In the meantime, pummel Sarge with rockets. Don't get to close to the columns and they energize and can electrocute you. He will roll around the outside of the room (when you shoot him with rockets) and pause at corners and in the middle to shoot BFG shots. Don't try to follow him: the floors fill in for him as he rolls, but open back up after he passes. It takes about 10-11 good rockets hits to kill him.

If you haven't taken everything yet, gather up the health, armor and ammo around the room. Then proceed into the area he came out of and you'll see a duct on the right. Duck into it, and follow it. Jump down onto the platform and go left. Pick up the armor shards, shells and 2 clips. Then go down the stairs and enter the elevator to move on to Site 3.