Ok, simply put, the drives, put in the different areas on floor 32, are attached to the metallic "grid" rooms. Each of these rooms will show a piece of one of the N4's past, it starts off with marelton showing he died in nuke town.
Here's a record of the other 6 drives:
-Misty 1: Misty's family is eaten by zombies, she as a teenager makes it out and runs away, only to end up in the clutches of the CDC.
-Samuel 1: Samuel is doing a lot of research about politicians and things, only to stumble upon a book left on the ground after what appears to be russman drops his stuff right outside this building. The book is none other then the Diary of Dr. Ludwig Maxis.
-Russman 1: It shows russman setting up a plan of attack on an area in germany, codename "project Arrow". Later it is shown russman takes up drinking to deal with the failed mission which causes the death of many of his squad.
-Marelton 2: Marelton flashes out of the sky Die-rise style in a Lab. He doesn't know where he is or why he's there. On the table is the body of a young-adult girl (misty). She is dead, but her brain seems perfectly preserved. Fallowing the math notes, marelton conducts his own experiments.
-Misty 2: It is shown many test were run on misty as she grew up in a lab, the final test seems to kill her. The scientist leave and the scene ends with marelton flashing into the room.
-Samuel 2: This scene shows the flesh cult forcing samuel to eat zombie flesh. He then appears immune, while the rest of the group turns zombie. In horror, he backs out of the ally to find russman in a bus, which quickly speeds off.
After unlocking these things you do NOT receive the achievement for revisiting your past. Because:
A: The last hard-drive doesn't appear to work.
B: There is one radio recording hidden around the lab for every room unlocked. A LOT of backstory info on this map!
Each of the radios can be found on the map somewhere. One is even in the very first spawn, meaning at least one player has to survive on the spawn platform until all the drives can be read, a HARD task, but not necessary for the easter egg, just the extra achieves:
-Marelton 1: ...Ate: Nov......9 my name is marelton Johnson! I am here, reporting my findings of the horrific practices being undertaken by this "pentageon" group every day for at least a decade. Reanimating the dead, super weapon technology, and horrific nazi underlying.I've tracked down everything I could, and........Richtofen... Who is richtofen? ... It's none of my concern, I'll let the american government decide what to do with this gro.....
-Misty 1: Today we acquired another test subject from our exposure site. We've named her Axis-21, formally known as "Abagail". I will personally be watching over her tests as she matures. This has been Dr. Kreizenburg, out.
- Samuel: The government today think's they're so smart... Well I'm on to them now... With the knowledge I've acquired from Mr. Romeros' office and this book which must have fallen from the heaven's above, I should find new hope in discovering the scourge of our american government!
Russman- Mr. Russman, you can not recover from this, you're old, life has moved on, it's time the department hired someone more modern. "I am an american government operative... You dare tell me ..." I was afraid you'd say this, but we can't have you blabbing to anyone about what you did... BANG.... (Noise like teleporting) What the hell...His body just... Vanished.... I must report this to Dr. Groph Immediately.
-Marelton 2:
Misty: Huh? Where am I?
Marelton: "Oh my god you're alive?!? IT WORKED?!?
Misty: Hey.... You..... Ug...
(zombie noises)
Marelton: No time to explain, let's get you out of here!
Misty: Rawr.... Zombies... Must... Kill zombies....
Marelton: Stick with me Mrs... .. GAH! ... My name... Is marelton.
-Misty 2:
A tragic end to our test subject came today. Odd thing too. It appeared JUST as soon as she fully lost consciousness she disapeared in a brilliant flash. This was odd, but what is even weirder is that hours later, she came BACK! Just popped up in the middle of shnenard's office, still dead... Just back.. We are running tests on the corpse now....
-Samuel 2:
Samuel: Uh... Hello? Who are you?
Name's russman! No time to talk, quick, shoot all these bastards off this bus!
Samuel: Who's driving this thing?
TEDD: Hello!
Samuel: What the f***!?!?!
Russman: Listen kid! We don't got time for this, shoot, kill, repeat. Or die trying! Keep it up, and we might just make it to the end of the line.
Samuel: What's the end of the line?
Russman: Step one....
-Russman 2 (This unlocks before the last grid chamber)
(silence)
Unknown voice: I'm coming for you Prometheus....
(Static)