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dd: /dee-dee/ [UNIX: from IBM JCL] vt. Equivalent to
   cat or BLT.  Originally the name of 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".  The UNIX `dd(1)' was
   designed with a weird, distinctly non-UNIXy keyword option syntax
   reminiscent of IBM System/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.
   The jargon usage is now very rare outside UNIX sites and now nearly
   obsolete even there, as `dd(1)' has been deprecated for a
   long time (though it has no exact replacement).  The term has been
   displaced by BLT or simple English `copy'.