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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