1. DDT
[from the insecticide para-dichloro-diphenyl-trichloroethene]
1. Generic term for a program that assists in debugging other
programs by showing individual machine instructions in a readable symbolic
form and letting the user change them. In this sense the term DDT is now
archaic, having been widely displaced by debugger or names of individual programs like
adb, sdb,
dbx, or gdb. 2. [ITS] Under MIT's fabled ITS operating
system, DDT (running under the alias HACTRN, a six-letterism for
‘Hack Translator’) was also used as the
shell or top level command language used to execute
other programs. 3. Any one of several specific DDTs (sense 1) supported on early
DEC hardware and CP/M. The PDP-10 Reference
Handbook (1969) contained a footnote on the first page of the documentation
for DDT that illuminates the origin of the term: Historical footnote: DDT was developed at MIT for the PDP-1
computer in 1961. At that time DDT stood for “DEC Debugging
Tape”. Since then, the idea of an on-line debugging program has
propagated throughout the computer industry. DDT programs are now
available for all DEC computers. Since media other than tape are
now frequently used, the more descriptive name “Dynamic Debugging
Technique” has been adopted, retaining the DDT abbreviation. Confusion
between DDT-10 and another well known pesticide,
dichloro-diphenyl-trichloroethane
C14H9Cl5
should be minimal since each attacks a
different, and apparently mutually exclusive, class of bugs.
(The ‘tape’ referred to was, incidentally, not magnetic
but paper.) Sadly, this quotation was removed from later editions of the
handbook after the suits took over and
DEC became much more
‘businesslike’. The history above is known to many old-time hackers. But there's
more: Peter Samson, compiler of the original TMRC
lexicon, reports that he named DDT
after a similar tool on the TX-0 computer, the direct ancestor of the PDP-1
built at MIT's Lincoln Lab in 1957. The debugger on that ground-breaking
machine (the first transistorized computer) rejoiced in the name FLIT
(FLexowriter Interrogation Tape). Flit was for many years the trade-name
of a popular insecticide.
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Definitions of DDT 
