Dynamic debugging technique

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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, 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. Early 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(and DDT-86 and DDT-68K) for their debugger, however, now meaning Dynamic Debugging Tool.[1][2] The CP/M DDT was later superseded by the Symbolic Instruction Debugger (SID,[3] ZSID, SID86,[4] and GEMSID) in DR DOS and GEM.[5][6]

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.[citation needed]

DEC-10/DEC-20 DDT[edit]

DDT (Dynamic Debugging Technique), as implemented on the DECsystem-10 & DECSYSTEM-20[7] 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.[7]

See also[edit]


  1. ^ Kildall, Gary Arlen (February 1978) [1976]. "A simple technique for static relocation of absolute machine code". Dr. Dobb's Journal of Computer Calisthenics & Orthodontia. People's Computer Company. 3 (2): 10–13 (66–69). ISBN 0-8104-5490-4. #22 ark:/13960/t8hf1g21p. Retrieved 2017-08-19. [1][2][3]. Originally presented at: Kildall, Gary Arlen (1977) [22–24 November 1976]. "A Simple Technique for Static Relocation of Absolute Machine Code". Written at Naval Postgraduate School, Monterey, California, USA. In Titus, Harold A. (ed.). Conference Record: Tenth Annual Asilomar Conference on Circuits, Systems and Computers: Papers Presented November 22–24, 1976. Asilomar Hotel and Conference Grounds, Pacific Grove, California, USA: Western Periodicals Company. pp. 420–424. ISSN 1058-6393. Retrieved 2021-12-06. (609 pages)
  2. ^ CP/M Dynamic Debugging Tool (DDT). User's Guide (PDF). Digital Research. 1976. Archived (PDF) from the original on 2007-07-06. Retrieved 2023-02-11.
  3. ^ SID Users Guide (PDF). Digital Research. 1978. 595-2549. Archived (PDF) from the original on 2019-10-20. Retrieved 2020-02-06. (4+69 pages)
  4. ^ SID-86 User's Guide for CP/M-86 (2 ed.). Digital Research. August 1982 [March 1982]. SID86UG.WS4. Archived from the original on 2019-10-20. Retrieved 2020-02-06. [4] (NB. A retyped version of the manual by Emmanuel Roche with Q, SR, and Z commands added.)
  5. ^ Paul, Matthias R. (1997-05-24) [1991]. DRDOSTIP.TXT — Tips und Tricks für DR DOS 3.41 - 5.0. Archived from the original on 2016-11-07. Retrieved 2016-11-07. {{cite book}}: |work= ignored (help)
  6. ^ Paul, Matthias R. (2002-01-09). "SID86". Newsgroupcomp.os.cpm. Archived from the original on 2018-08-27. Retrieved 2018-04-08. […] Since the DR-DOS 7.03 DEBUG is still based on the old SID86.EXE, I suggest to run DEBUG 1.51 and enter the extended help system with ?? from the debug prompt. This will give you eight screens full of syntax and feature help. Some of these features were also supported by older issues. […]
  7. ^ a b Bering, Douglas E. (1975) [1968, 1969, 1970]. "Intro". Reference Manual: DDT (Dynamic debugging technique) and TDT (Tracing debugging technique. National Technical Information Service]. DEC-10-UDDTA-A-D. DDT (Dynamic debugging technique) and TDT (Tracing debugging technique) for PDP-11 systems

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