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DDT is closely related to [[Octal Debugging Technique|ODT]]. Both names were used for several different debuggers, but generally debuggers with the ODT name had more limited capabilities than DDT debuggers.
{{anchor|CP/M}}Early versions of [[Digital Research]]'s [[CP/M]] and [[CP/M-86]] kept the DEC name DDT (and DDT-86<!-- with hyphen -->) for their debugger, however, now meaning "'''Dynamic Debugging Tool'''".<ref name="Kildall_1978_DDT"/> The CP/M DDT was later superseded by [[Symbolic Instruction Debugger|SID]] and SID86<!-- no hyphen --> (for "Symbolic Instruction Debugger").
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, it is replaced with a "PWORD" which implements a restricted subset of DDT's functionality. 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"); thus [[Guy L. Steele]]'s famous [[filk]] poem parody of [[Edgar Allan Poe]]'s "[[The Raven]]," ''The HACTRN''.
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