 SHRDLU was written in the Micro Planner and Lisp programming language on the DEC PDP-6 computer and a DEC graphics terminal.Later additions were made at the computer graphics labs at the University of Utah, adding a full 3D rendering of SHRDLU's "world".The name SHRDLU was derived from ETAOIN SHRDLU, the arrangement of the letter keys on a Linotype machine, arranged in descending order of usage frequency in English.