E1M6: Central Processing (Doom)

E1M6: Central Processing is the sixth map of Knee-Deep in the Dead in Doom. It was designed by John Romero and uses the music track "On The Hunt". The par time is 3:00.

It is well known for its traps, which when triggered opens up rooms of monsters and often simultaneously shuts the escape doorway. In co-op mode, it is possible to have your buddy stand in the doorway, which will prevent the triggered door from closing, thereby providing an exit from having to fight numerous enemies in close quarters.

Walkthrough

 * Letters in italics refer to marked spots on the map. Sector numbers in boldface are secrets which count toward the end-of-level tally.

Essentials
Head north from the start point (A) and take the first walkway to the east. Follow the walkway into a large rectangular room and pick up the red keycard at the far end (B). As you enter this room, the entrance will close behind you, then reopen after 30 seconds. Go back to the walkway and follow it to the west, where you will find two red doors (C). Open either door and follow the tan passage around to a triangular pier, at the end of which is the blue key (D), overlooking a nukage pool. As you leave the tan passage to get the key, a trap opens behind you (E), releasing a Demon (I'm too young to die and Hey, not too rough), or an Imp and a Demon (Hurt me plenty), or two Imps and a Demon (Ultra-Violence and Nightmare!).

Now return to the start area and go through the gray door to the north, which leads to a dark computer room (F). Exit to the east and cross the walkway to the blue door (G). Beyond the blue door is a maze of tan passages and small slime pools. This maze can be navigated using the left-hand rule (turn left whenever you can, and turn right only when you have no choice). If you do so, you will eventually come to the switch at the extreme southern end of the maze (H), which opens a tall green door on the west side of the maze. Continue following the left-hand wall until you reach this door (I), and you will see the yellow key atop a short staircase (J), along with a backpack. As you reach the top of the staircase, a trap opens behind you (K), releasing a Spectre (ITYTD and HNTR), or two sergeants, an Imp, and three Spectres (HMP), or four sergeants, an Imp, a Demon, and three Spectres (UV and NM).

Return to the dark computer room and leave through any of the yellow doors to the north. You will reach a landing above a large nukage pool. Go down the stairs to the north, around the walkway, and up another staircase to a switch between two candelabras (L). This switch opens the large gray door to the west of the pool (M). Run across the nukage and through the doorway; the door closes behind you, but reopens after 30 seconds. Take either the left or right staircase downward into a blue computer room. In an alcove on the east wall, there is a switch (N) which opens part of the north wall, exposing the exit room (O). As you approach the switch, however, two large traps (P, Q) open on the west and south walls, and the staircases back to the nukage room are sealed off (though they open again after 30 seconds). The exit room itself is guarded by a Spectre (ITYTD and HNTR), or four Spectres (HMP), or seven Spectres (UV and NM).

Other points of interest
In the first room, the northeast wall of the large slime pool contains a narrow doorway (R) through which some barrels are visible. This small room holds a green armor, three medikits, three shell boxes, and one or more Imps. The Imps can easily be killed by shooting the barrels from the walkway.

As you take the red key, five traps will open in the walls of the room, releasing a crowd of monsters. This is especially dangerous if the door of the room is still sealed. With great care, it is possible to get the key without triggering the traps. Alternatively, pick up the chaingun and the bullet boxes first, open the traps, then run past the monsters to the entrance and hide around the corner (S); a monster-blocking linedef prevents anyone else from entering the tan area, so you cannot be surrounded. Note that all monsters in the traps are deaf, and in fact one sergeant in the western trap usually does not notice you as you run out.

As you approach the blue door, a trap opens in the south wall of the slime room behind you (T), revealing a sergeant (ITYTD and HNTR), or two sergeants, a Demon, and a Spectre (HMP), or two sergeants, three Demons, and a Spectre (UV and NM). The new alcove also contains a medikit and a radiation suit.

If you solve the maze using the route described above, you will approach the switch through a curving tan passage along the southeastern boundary of the map. This passage also includes a bullet box, a shell box, and a discolored panel with armor bonuses arranged nearby in the shape of an arrow (U). Activate the panel to reveal a computer map. (The small room is not needed for 100% secrets.)

Behind the outer columns in the large nukage pool are a stimpack, a box of bullets, a radiation suit, and a medikit (clockwise from northwest column).

Between the downward staircases leading to the blue computer room is an upward staircase, which leads to a balcony (V) containing a medikit and a bullet box.

When approaching the switch in the blue computer room, if you enter the alcove extremely slowly, you can trigger the traps (W) without closing the escape routes (X). In co-op mode, it is also possible to have your comrade stand in the doorway, which will prevent the triggered door from closing (as with the speedrunning "door trick" described below).

Secrets

 * 1) Across the nukage pool from the blue keycard is a dark doorway.  As you enter the passageway beyond, a platform will lower in front of you (sector 169).  Get on the platform and ride up to obtain a soul sphere (Y).  (You may want to visit the north corner of the pool first; an alcove there contains a radiation suit (Z).  After picking up the key, face northwest, run forward off the side of the pier, then make a hairpin turn to your right.)  To exit the pool, see secret #2 below.
 * 2) In the east corner of the same nukage pool is a platform (AA) with a medikit and a blue armor.  The adjoining staircase (sector 181) leads to a blur artifact, a light amplification visor, and two boxes of rockets.  Click the wall switch to open a one-way door back to the start point.
 * 3) A short passage (BB) connects the blue door room (activate the south wall of the trap) and the yellow key room (activate the south wall at the top of the stairs).  It contains a rocket launcher, a blur artifact, and a backpack (sector 190).  The blue key is required to exit this passage to the northeast, but if you have it, you can get the yellow key without entering the maze.
 * 4) Crossing between the two lowest steps in the yellow key room opens a blocked slime passage (CC) leading northward from the blue door room; this releases two Imps (ITYTD and HNTR), or three Imps (HMP), or five Imps (UV and NM).  The slime passage eventually reaches a hidden platform with two medikits, several large ammo pickups, and a backpack (sector 65).  You can then open the door to the north and jump down into a brown courtyard (DD) containing a soul sphere (guarded by seven sergeants on UV and NM).  The soul sphere is on a column which lowers as you approach it; the adjacent wall is a one-way door which leads to the northeast corner of the large nukage pool (EE).  Note that this route allows you to complete the level without picking up the yellow key, but once you have entered the courtyard, you are confined to the northern part of the level.

Bugs
In UV and NM, two Demons are stuck together near the radiation suit in front of secret #3 (see screen shot below). This leaves them very vulnerable to the nearby barrel, and traps another Demon and a Spectre behind them until one is killed. The latter two monsters can still pursue the player if approached from the south, however.

In UV and NM, a Spectre is embedded in the north wall of the exit room. Although he cannot move, he will attack if approached closely.

The following actions can trigger the blockmap bug:


 * Firing eastward or westward at the north edge of the slime walkway in the first room.
 * Entering the first room from the south (via secret #2).
 * After leaving the first maze room to the east, turning right to face the first Imp (ITYTD and HNTR) or the first two Imps (HMP, UV, and NM).
 * Leaving the dark computer room by the west door, passing the column at the top of the stairs, then firing eastward.

Slime trails may be visible in the following locations (see screen shots below):


 * On the western part of the walkway in the first room, looking east along the south edge.
 * Opening the blue door from the left side.
 * Looking back into the maze through the tall green door.
 * Looking into the brown courtyard (secret #4) from near the northeast corner of the large nukage pool. (Strangely, if you are actually in the courtyard, no bug seems to occur.)
 * From the same courtyard, looking in through the south grate (again, this disappears at close range).
 * Looking back into the south staircase from the blue computer room.

There are 7 known anomalies in this level's REJECT table.

Demo files

 * [[Media:e1m6secr.lmp|No monsters, 100% secrets walkthrough]] (file info)
 * [[Media:e1m6wik1.lmp|100% kills, items, and secrets on ITYTD]] (file info)
 * [[Media:e1m6wik2.lmp|100% kills, items, and secrets on HNTR]] (file info)
 * [[Media:e1m6wik3.lmp|100% kills, items, and secrets on HMP]] (file info)
 * [[Media:e1m6wik4.lmp|100% kills, items, and secrets on UV]] (file info)

The "door trick"
If a monster is standing under the door to the red key room, it will not close. The player can therefore save 15-20 seconds at the start of the level by:


 * lunging forward to attract the attention of the two sergeants in the tan area;
 * taking cover so that the sergeants advance along the walkway;
 * running into the red key room just as the left-hand sergeant reaches the doorway.

The second step is essential with fast monsters, who prefer to keep shooting as long as you are in view, although in UV it has been demonstrated that it is possible to kill the left-hand sergeant with the pistol (avoiding the slight detour to the shotgun pickup), by which time the right-hand sergeant is under the door. This is normally not done in runs requiring 100% kills, however, because it is more efficient to destroy the barrels in the green armor room while the left-hand sergeant is walking forward. Some NM100S players even pick up the green armor during the delay.

In early Compet-N recordings, to conserve health, players instead killed these two sergeants immediately and waited for the first Imp to approach the door from the outside, triggering the closing door when the imp blocked it. This variant is still used in Nightmare! movies, since the player often cannot afford the health loss from the two sargeants.

Although the trick is widely applicable, it is rarely used in UV -fast recordings: the player finds himself standing in the tan area anyway in order to be sure of hitting the fast Spectres (the closed door is actually helpful, as it blocks attacks from behind), then picking up the health in the traps after everyone is dead, by which time the door has opened.

Maze routes
The ideal route through the maze is a matter of debate. Most, but not all, Compet-N runs proceed counterclockwise around the edge until they reach the switch, take the central passage toward the tall green door, then leave via secret #3. Common variations include using the southwestern passage instead of the central one. Tyson recordings often exit the maze to the north, the better to encourage infighting by rapidly opening and closing the blue door.

Anders Johnsen advocates using the central passage instead of the southeastern one for UV max, since the latter contains no deaf monsters. He credits this idea to Yonatan Donner and Peo Sjöblom.

Radek Pecka, in setting the UV -fast world record, improved on the previous record by 33 seconds. His unconventional maze route is shown in the figure.

Early UV -respawn runs attempted the obvious optimization, avoiding the maze altogether by spending more time in the red key room and the blue door room, but it is actually faster to clear the maze (see below).

Pacifist entrants are forced into the maze to obtain the yellow key, as it would take too long (and waste too much health) to clear the alcove in front of secret #3 using infighting. For the same reason, they must leave the maze the way they came in.

The exit area
In most categories, a successful run usually clears the entrance to the tan staircase with rockets from the nukage walkway, then clears the large traps with rockets from the switch alcove. This requires conserving not only rockets but health; as Ian Sutton observes, "Your worst enemy is yourself at the end where you can easily blow yourself to smithereens if not careful". For maximum speed, the red switch should be pressed as the traps open, so that blast damage affects as many enemies as possible. Some players lunge forward to fire a dispersed volley before retreating into the alcove; others never leave the alcove until only a few rockets remain, so as to delay the monsters in the south trap (who are all deaf). A few Compet-N recordings manage to avoid self-inflicted damage entirely, though it is not clear that this is reproducible. Weaving from side to side in the alcove does seem to discourage Demons and Spectres from entering it. Some players think it important to aim at the barrels, because the blast damage pushes them into the ranks of the enemy as they explode.

In a straight speedrun, it is also possible to activate the switch and then reach the exit without firing a shot. Run forward out of the alcove, and swerve to the right as you reach the crowd; with luck, the monsters already outside the trap will be hit by friendly fire from inside, and decide not to block your path. With fast monsters, it may be necessary to push the last few Spectres aside with the chaingun. While this strategy allows you to clear the tan staircase faster, by using rockets instead of bullets, the final dash to the exit carries a high risk of becoming surrounded, or at least delayed for many seconds. The two maneuvers can be combined: fire all of your rockets, click the switch, feint to the west to spread the Spectres out somewhat, then press toward the exit with the chaingun.

After the traps have been dealt with, some players make a point of picking up the rocket in the corner and using it in the exit room. Because the Spectres in front of the exit door are crowded so close together, however, the player may charge forward only to find that one of these has also remained in place.

NM runs, with their doubled ammo pickups, easily allow the player to clear the area behind the gray door with rockets instead of bullets. Some players prefer to fire only a few rockets from the large nukage pool, then push the Imps on the staircases aside with the chaingun.

In the blue computer room, some Tyson players shoot each barrel once before opening the traps, to encourage barrel frags. To save time via infighting, the player can also take the highly dangerous step of opening the exit room along with the traps.

Due to the large population of this area, Chris "Ryback" Ratcliff's original pacifist recording was brought up short at the large nukage pool; he gradually emptied the slime room with infighting, then cleared the gray doorway even more slowly by baiting a single Imp into firing toward it over and over again. Adam Williamson then demonstrated that, by walking slowly along the wall in the southeast corner of the blue computer room, one could separate the monsters in the traps sufficiently to weave one's way among them (thereby reducing the Compet-N record from 65:14 to 2:32). He credits Jonathan Rimmer with inventing the trick. Later recordings further improved the time by dodging the Imps on the tan staircases at close range, which had previously been thought impossible. Some players also destroy the barrels in the blue computer room before opening the trap, to make evasion easier, or fire a bullet at the red switch to arouse the Spectres sooner.

In episode runs, particularly with fast monsters, most players clear this area with the chaingun to avoid injuring themselves (possibly running out of bullets before reaching the exit room).

Other tactics
In a straight speedrun, the shortest route is to get the yellow key through secret #3, bypassing the maze, then leave the dark computer room through the yellow door to the east. For maximum speed, the shotgun should be used only until the chaingun is picked up, then wielded briefly in the yellow key room to avoid firing a rocket at close quarters (which can be done, but the additional stride to the back wall may waste time). The immobile Demons near secret #3 help keep the path through the alcove clear, although this is slightly less reliable in NM speed, as it takes more than eight seconds to pick up the yellow key and return to the walkway. If a bullet is fired as the yellow door opens, there will be slightly less traffic at the bottom of the next staircase. In an episode run, the player may well obtain the chaingun on this level: the other four were simply too far out of the way.

Adam Williamson points out that the UV speed record for E1M6 is faster than the level time in Doom Done Quicker, because the total episode time can be lowered by carrying a few rockets into E1M7 and E1M8. In episode runs, secret #4 is often entered even when not required, for the extra ammo and health.

In principle, NM speed runs could use the UV speed route, but the blue armor proves to be indispensable protection; all but the fastest Compet-N entries collect the nearby soul sphere as well. Similarly, although the soul sphere is not part of secret #1, it is obtained in nearly every NM100S recording (and when it is not, every one of those 19 medikits becomes quite valuable). Some NM100S players fire several rockets through each grate in secret #4, clearing most of the route to the gray door switch.

When 100% kills is required, rockets generally must be stockpiled for the final few rooms. Their next most common use is in the secret courtyard: to finish off the sergeants quickly, to clear the area near one of the grates, or even to kill a few monsters beyond the hidden door (there is just about enough time to step back, fire, then step forward again before the lift rises). The fastest runs also use several rockets in the yellow key trap and before crossing into secret #4, although the player does tend to take blast damage, and in fact must fire out of secret #3 at an angle when fast monsters are used. One further optimization, due originally to Jonathan Rimmer, involves shooting the last Imp at the yellow key from halfway up the stairs:


 * The Imps in the slime passage start to approach the alcove, so that some of them are killed by stray rockets as you pass through it.
 * The monsters in the yellow key trap remain close together; sometimes three rockets and one shotgun round are enough.
 * Since it takes less time to cross to the slime passage, the radiation suit is still in effect when you reach the large nukage pool. You can then run to the south end of the pool and pick off some zombies on the landing, which saves more time.

In an episode speedrun, because rockets tend not to be used in the exit area, the yellow key room can be cleared from a distance before the trap even opens.

Because the level contains many more shells than bullets, the speed of a max run depends greatly on when the chaingun is used. Ideally, the dark computer room is the only crowded area which must be cleared with the shotgun: players typically pause in the center to kill the two deaf monsters, then make their way to the lift at the north end, where only one or two enemies can approach at a time. With fast monsters, however, a Demon can bite more quickly than the shotgun can reload, so the chaingun must be used here also (and therefore less, perhaps, at the large nukage pool). In any case, it is important to keep moving in dead ends, to stay out of the Demons' melee range.

Expert players resist the temptation to open fire immediately at the red key, instead waiting until the monsters approach the center of the room. It is not unheard of to kill all but two or three with barrel frags.

The fastest UV -respawn runs follow the UV max route exactly; as with E1M4, it is unnecessary to clear any room twice. The elapsed time is always a bit longer, however, because some monsters in the first room have respawned by the time secret #2 is obtained; spending a few extra seconds in the blue computer room is prudent as well, just to be on the safe side. Early Compet-N recordings also skipped the dark computer room and the yellow key trap in favor of more kills in the exit area, but it is actually more efficient to clear the yellow key trap, because that allows the monsters in the dark computer room time to reach the alcove in the blue door room, where they can be shot with rockets.

Because there is no chainsaw here, a Tyson player must rely heavily on infighting, especially by using Demons and Spectres to shield himself from ranged attacks. It is useful to lead the Demons from the dark computer room into the blue door room, where they can be attacked by Imps as secret #3 and secret #4 are opened. The fastest recordings are achieved by consistently punching monsters from behind while this occurs (at the entrance to the tan staircases, for example); the player is advised to take the radiation suit in the blue door room as soon as it appears, to gain more maneuvering space while dodging Demons. If the sergeants in secret #4 are awakened from above, a few of them will probably kill each other before they must be faced at close range. In a Tyson episode run, the chainsaw permits a somewhat more straightforward approach than the above (especially in crowded areas like the red key room and the dark computer room), although infighting is still important in the exit area.

Some Tyson runs use a lot of bullets in the first room to save time, then use the fist in the maze; others use bullets in the maze to conserve health, then save time by directly assaulting the blue door room on the way out. All Compet-N entries to date have picked up the first soul sphere. The Spectre near the yellow door should be punched from the north, so that it is unlikely to move.

Not surprisingly, pacifist runs invariably detour from the UV speed route at the blue key to pick up the blue armor and the soul sphere. A few seconds can be saved, at the expense of a few hit points, by getting the soul sphere first. The partial invisibility in secret #2 also helps protect the player from the zombies near the large nukage pool. Adam Williamson's groundbreaking recording demonstrated that the second soul sphere can be skipped; in addition, he noted the importance of adjusting one's footwork slightly to use pillars as cover, even in the large nukage pool (which does contain a radiation suit).

Current records
The Compet-N records for the map are:

Inspiration and development
Early versions of this map appeared as E1M5 of Doom 0.4 and E1M9 of Doom 0.5.