Editing Dynamic debugging technique (section)

{{Short description|Series of debugger programs}}
{{Use dmy dates|date=July 2019|cs1-dates=y}}
{{Use list-defined references|date=January 2022}}
[[File:Digital Research CP-M-86 for the IBM Personal Computer Version 1.0 720x400.png|thumb|300px|<code>DDT86.CMD</code> in [[Digital Research]] [[CP/M-86]] for the [[IBM Personal Computer]] Version 1.0]]
'''Dynamic Debugging Technique''' ('''DDT''') is a series of [[debugger]] programs originally developed for [[Digital Equipment Corporation]] (DEC) hardware, initially known as '''DEC Debugging Tape''' because it was distributed on [[paper tape]].  The name is a pun on the insecticide [[DDT]]. The first version of DDT was developed at [[MIT]] for the [[PDP-1]] computer in 1961, but newer versions on newer platforms continued to use the same name. After being ported to other vendor's platforms and changing media, the name was changed to the less DEC-centric version. {{anchor|CP/M}}Early versions of [[Digital Research]]'s [[CP/M]] and [[CP/M-86]] kept the DEC name DDT (and DDT-86 and DDT-68K<!-- both with hyphen -->) for their debugger, however, now meaning '''Dynamic Debugging Tool'''.<ref name="Kildall_1978_DDT"/><ref name="DR_1976_DDT"/> The CP/M DDT was later superseded by the ''[[Symbolic Instruction Debugger]]'' (SID,<ref name="DR_1978_SID"/> ZSID, [[SID86]]<!-- no hyphen -->,<ref name="DR_1982_SID86"/> and [[GEMSID]]) in [[DR&nbsp;DOS]] and [[Graphics Environment Manager|GEM]].<ref name="Paul_1997_DRDOSTIP"/><ref name="Paul_2002_DEBUG"/>

In addition to its normal function as a debugger, DDT was also used as a top-level [[command line interpreter|command shell]] for the [[Massachusetts Institute of Technology]] (MIT) [[Incompatible Timesharing System]] (ITS) [[operating system]]; on some more recent ITS systems, "PWORD"—which implements a restricted subset of DDT's functionality—is run first and is overlaid with DDT as soon as the user logs in. DDT could run and debug up to eight [[Process (computing)|processes]] (called "jobs" on ITS) at a time, such as several sessions of [[Text Editor and Corrector|TECO]], and DDT could be run [[recursively]] - that is, some or all of those jobs could themselves be DDTs (which could then run another eight jobs, and so on). These eight jobs were all given unique names, and the usual name for the original and top-most DDT was "HACTRN" ("hack-tran"). [[Guy L. Steele]] wrote a [[filk]] poem parody of [[Edgar Allan Poe]]'s "[[The Raven]]," entitled ''The HACTRN''.{{fact|date=April 2020}}