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dd: /dee·dee/, vt. [Unix: from IBM JCL] 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’.
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