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 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
DCS « DCT « DD « dd » DDB » DDCMP » DDE