Contents page

Index (83KB)

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 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).