DDT86.CMD
| Company type | Software |
|---|---|
| Industry | Computer software / Debugging tools |
| Founded | 1961 |
| Headquarters | United States |
| Products | Debugger software, command shell (on ITS) |
Dynamic Debugging Technique (DDT) refers to a collection of debugger software initially designed for Digital Equipment Corporation (DEC) machines. Its original name, DEC Debugging Tape, stemmed from its distribution format on paper tape. The title cleverly alludes to the pesticide DDT. The inaugural version was developed at MIT in 1961 for the PDP-1, with subsequent releases on newer hardware preserving the DDT designation. As its use expanded beyond DEC platforms, the meaning of DDT shifted to Dynamic Debugging Tool. Early iterations of Digital Research's CP/M and CP/M-86 continued to use the DEC-associated DDT label for their debuggers (such as DDT-86 and DDT-68K). Eventually, CP/M’s DDT was superseded by the Symbolic Instruction Debugger family (SID, ZSID, SID86, and GEMSID) within DR DOS and the GEM environment.
In addition to its debugging capabilities, DDT functioned as a primary command shell on MIT’s Incompatible Timesharing System (ITS). On certain ITS installations, a minimal version named "PWORD" executed initially and was replaced by DDT upon user login. The debugger could handle up to eight simultaneous processes—referred to as "jobs" on ITS—including recursive invocations of itself. Each job was assigned a distinct identifier; the original top-level instance was commonly known as "HACTRN." Among its cultural footnotes, Guy L. Steele authored a filk parody of Edgar Allan Poe's "The Raven" entitled The HACTRN.
DEC-10/DEC-20 DDT
On the DECsystem-10 and DECSYSTEM-20, DDT provided symbolic debugging by loading symbol information directly from the .EXE executable file under examination. A specialized version called SDDT accessed symbols from the active monitor, enabling system developers to analyze internal system behavior.
External links
- DDT Command List – freeware implementation written in portable C
- ITS 1.5 Reference Manual – Artificial Intelligence Memo No. 161A
- ITS: Luser's Guide
- The Great Quux Poem Collection – featuring commentary on the poem The HACTRN