dd

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" 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" has been deprecated for

a long time (though it has no exact replacement). The term

has been displaced by BLT or simple English "copy".

[Jargon File]

(1995-02-03)