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. Under MIT's fabled ITS operating system, DDT (running under the alias HACTRN) was also used as the shell or top level command language used to execute other programs.

3. Any one of several specific debuggers supported on early DEC hardware. The DEC 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 (C14-H9-Cl5) 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 transistorised computer) rejoiced in the name FLIT (FLexowriter Interrogation Tape).

(01 Jul 2002)

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This chlorinated organic insecticide was discovered by Swiss chemist Paul Muller in 1939.

DDT has been especially useful in controlling mosquitos that carry malaria, but some strains of the insects have become resistant to it. DDT has comparatively low acute toxicity in humans (it is thought to cause cancer), but it persists for a longtime in the environment and is disastrously toxic to birds, especially top-level predators such as hawks and eagles.

The chemical interferes with the birds ability to metabolise calcium, and thus affected birds that lay eggs with fatally thin shells. DDT has been banned in most countries, but it is still widely used on crops in Latin America.

(09 Oct 1997)

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