DDT

DDT /D-D-T/ n.  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) 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.  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 {suit}s 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).