The DHARMA manuals were a series of binders found by Sayid in the Flame station in "Enter 77". Sayid looked at one about the food drop and then one about operations. The operations manual contained a map of the cable system and showed the location of the barracks. It also (most probably) contained plans of The Looking Glass. DI 90M1654-21644 was the code that appears on the manuals. "DI" was likely an abbreviation of "DHARMA Initiative".