dd

/deedee/ , 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.

