DDT

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).

[Jargon File]