"Aside from your weapons and your wits, one of the most important assets in DOOM3 is your PDA (Personal Data Assistant), which stores vital information that you’ll need to get through the game. You can review your current objectives and read a brief summary of any weapons you are carrying, and pick up someone else’s PDA and download its information into yours—E-Mail, video discs (which you can also find lying around), audio logs, access codes to secured storage lockers containing Med Kits, armor, ammo and occasionally weapons. Most important, you can update your security clearance to unlock doors to previously inaccessible areas of the base.

The E-Mails and audio logs fill you in on the events that led up to the present catastrophe before your arrival on Mars, and does a nice job of fleshing out DOOM3’s storyline. The video discs are mostly slick UAC "infomercials," although you may occasionally run across that may prove useful."