Dynamic Debugging Technique

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Series of debugger programs

title: "Dynamic Debugging Technique" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["debuggers", "digital-equipment-corporation", "cp/m", "command-shells"] description: "Series of debugger programs" topic_path: "general/debuggers" source: "https://en.wikipedia.org/wiki/Dynamic_Debugging_Technique" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Series of debugger programs ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/f/f2/Digital_Research_CP-M-86_for_the_IBM_Personal_Computer_Version_1.0_720x400.png" caption="DDT86.CMD 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. It was an adaptation of the pioneering interactive, symbolic debugger FLIT which had been developed for MIT's TX-0 computer in 1959. Newer versions of DDT 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. CP/MEarly versions of Digital Research's CP/M and CP/M-86 kept the DEC name DDT (and DDT-86 and DDT-68K) for their debugger, however, now meaning Dynamic Debugging Tool. The CP/M DDT was later superseded by the Symbolic Instruction Debugger (SID, ZSID, SID86, and GEMSID) in DR DOS and GEM.

In addition to its normal function as a debugger, DDT was also used as a top-level 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 processes (called "jobs" on ITS) at a time, such as several sessions of 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.

{{anchor|TDT}}DEC-10/DEC-20 DDT

DDT (Dynamic Debugging Technique), as implemented on the DECsystem-10 & DECSYSTEM-20 allowed references to symbols within the programming being debugged. This feature loaded symbols from the .EXE executable file; a special version named SDDT used symbols from the running monitor and allowed system programmers to "peek" inside.

References

References

  1. National Museum of American History, Smithsonian Institution. (November 29, 2018). "Interview with Robert Alan Saunders". National Museum of American History, Smithsonian Institution, Washington, DC.
  2. McKensie, John A.. (1 October 1974). "TX-0 Computer History".
  3. (February 1978). "A simple technique for static relocation of absolute machine code". [[People's Computer Company]].
  4. (1978). "SID Users Guide". [[Digital Research]].
  5. (1976). "CP/M Dynamic Debugging Tool (DDT). User's Guide". [[Digital Research]].
  6. (August 1982). "SID-86 User's Guide for CP/M-86". [[Digital Research]].
  7. (1997-05-24). "DRDOSTIP.TXT — Tips und Tricks für DR DOS 3.41 - 5.0". MPDOSTIP.
  8. (2002-01-09). "SID86".
  9. (1975). "Reference Manual: DDT (Dynamic debugging technique) and TDT (Tracing debugging technique". National Technical Information Service].

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debuggersdigital-equipment-corporationcp/mcommand-shells