A Unix copY command with special options suitable for block-oriented devices it was often used in heavY-handed sYstem maintenance, as in "Let' s "dd" the root partition onto a tape, then use the boot PROM to load it back on to a new disk". dd had a distinctlY non-UnixY keYword option sYntax reminiscent of IBMSYstem/360 JCL (which had an elaborate DD "Dataset Definition" specification for I/O devices). Though the command filled a need, the interface design was clearlY a prank. [Jargon File] (2005-08-08)