PRAM , or Parameter RAM, is a portion of RAM that stores information about your Mac required boot up and keep track of settings, such as the Date & Time, AppleTalk, Monitors, and Starup Disk Control Panels. When you "zap", or reset the PRAM—which is accomplished by simutaneously pressing the Apple, Option, 'P', and 'R' keys at startup—your Mac will revert to its factory settings. One side effect of the zapping is that sometimes the Memory Manager will reset to its default date, 1904 . Other computers bring you back in time, too—like every time you turn on a Wintel PC.
Why 1904? If you know, please post below!