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.

This level open with a cinematic in which you see Elliot Swann's bodyguard walking through Central Processing, hunting someone.

Your mission is to stop Sarge. Start by going down the hallway after the bay door opens and and bearing left. You'll see a glass window on your left, which will break as two imps teleport in: one in the room with the window, and the other behind you in the hallway. Kill them and proceed through the window (the door is locked). Grab the shotgun, 2 boxes of shells and bullets on the table. You can use the screen at the desk to open a security locker to your right, which contains 50 armor. There is an emergency medical station with 80 health if you need it. You'll also see locker 452 to your left. The code is 571. Pick up the rocket launcher, rockets and grenades.

Go through the door. Go left and you'll see a hallway. You'll get ambushed by three cherubs. Kill them, and proceed down the hallway. There will be a door on your left. if you open it, an imp will come out. Kill him, and keep going (nothing interesting in the office). There be another door on your left, this time with an office that has some plasma and clips. Grab it, go out, and continue. You'll get to the end of the hallway and an archvile will spawn, kill him and you'll hear a cherub behind you, down the hall. Kill it, and then go back to the door where the archvile spawned. It will ask for a code. New mission: Obtain access code for Lab A.

Head back to the area where you walked in. You'll see an office area with broken windows around it. If you jump-crouch to get in, there is another emergency medical station with 50 health, some armor shards, and a box of shells if you need to stock up.

Go back out of the office area, and walk up to the door with the sparking panel across from the office. You'll get another new mission: find a replacement panel in Lab A to gain access to this area (the data library).

Turn around and head down the hallway. You'll see a green panel and the door will open as you walk up. Go through and jump across the panels that hover over the lava. Go through the next door. Inside is a small security area. Go through it into the offices. As you walk in, an imp and 4 spiders will spawn. If you kill the 4 spiders, 3 more will spawn, and if you kill the imp, another will spawn. Head straight to the back of the room (with the yellow lights).

You will hear a whip-soldier running in the same way you came in. Kill him, and as you do, another will spawn in the back of the room (where you triggered the first). Kill him. There area is now clear (kind of). Go right from the entrance, down the stairs. Walk up to the desk and you'll see two panels: one controlling security camera images and one showing the images. If you press "Main Entrance Hall" you'll get no picture and a spider will crawl out from behind the monitor. The easy way to get the code is to press "Lab A Meeting Room" which shows a giant "627" on the screen.

The harder way is to go over to the left of the entrance. Grab the box of shells, 3 bullet packs, and 2 plasma canisters. Continue into this area and you will see a screen that controls a maintenance storage hatch. Open it, and then go back out of this area, keeping the wall on your left. Eventually, just to the left of the big red screen, you'll see a open hatch in the wall under a yellow light. Go in and grab the shells and Tony Bates PDA. If you listen to the audio log, you'll hear him mention 627 as the code. Go all the way back to the door that needed the code and enter it. On the way, you'll get some kind of enemy spawn in the main area. It could be just an imp and a cherub, or a couple of cherubs and an archvile.

Go inside and turn right and go down the hall. You'll see a cinematic where the whole hall melts into a hellish pit. You'll need to sprint to make the jumps across the remaining panels. Once you get to the next section of hall, keep going and go through the door. You'll see a server rack ahead of you, go behind it and pick up the 50 armor.

Turn right from the entrance and go down the passage. Kill the two cherubs that ambush you. You have a choice: the fast path or the hard path.

HARD PATH: keep going around until you get to a door. At this point, 2 cherubs, an imp, and 2 wraiths will be after you. Kill them, pick up the shells, clips, bullets and 2 plasma canisters from this area. Turn around and pick up Charlie Haskell's PDA. Go through the door out to the hellish looking area, jump across the lava, and grab the ammo belt, 50 armor, and rocket launcher. Go back to the area where you made your choice to take the hard path. You'll have to fight an imp and a whip-soldier on your way back, and 2 more cherubs will await you by the elevator.

EASY PATH: don't go straight. You'll see an elevator on your right, use it to go up a floor. You're on "CPU Banks A-J", so press "CPU Banks K-T".

A wraith will greet you as you come out the elevator. Head straight and bear right. An archvile will spawn. Kill him quick (or he'll spawn other monsters). Turn left (or right) and proceed by going around the server cluster. You'll see an elevator on the other side. Use it to go to Floor 3: Routing.

As you exit, you'll be greeted by 4 cherubs and an imp. Go straight back all the way, and then turn right. Kill the whip-soldier that comes through the door, and go through the door. You be ambushed by two imps from either side. Kill them. If you jump across the horns coming through the floor rather than re-routing through the office, you'll miss 2 imps and a cherub, but you'll also miss 3 boxes of shells, 2 plasma canisters and some armor shards. Get to the other side of the obstruction in the hallway, and go through the door. Follow the path around, kill the imp.

If you took the hard path, you'll have Charlie Haskell's PDA which tells you the code to locker 669 is 468. Open it and grab the 50 armor, 2 plasma canisters, and grenades. If you need health there is 3 30 health packs. As soon as you grab the panel and the health packs on the right locker, demons will spawn: 8 spiders and an imp.

As you leave, an archvile will spawn, and soon after (past the horns in the hallway again) another 2 cherubs. After you take the elevator down to the second floor, 8 wraiths will spawn and hunt you. Take the next elevator down to floor 1, and go back to the main area to install the panel at the door to the data library.

Go inside and follow the hall. You'll see a small office off the the right. You can go in and grab 30 health, but you'll have to kill a spider. Proceed down the hall and open the door labelled "CPU Core". Kill the two imps inside and take the elevator down to sublevel 1: Main CPU. Its a scenic ride, if you look out the back window of the elevator.

Once you get to the sublevel, follow the halls and you'll see Elliot Swann's bodyguard, as he dies, will tell you that Sarge has his gun (the BFG). The you'll hear Sarge's voice: "I killed that pathetic bodyguard and now I'll kill you." You'll see a missing floor panel. Go through it and pick up the armor shards, health, rockets and plasma canisters. Go back to the area where the bodyguard is and open the bay door to move on to the Central Server Banks.