Dynamic debugging technique
| Company type | Software |
|---|---|
| Industry | Computer software, Debugging tools |
| Founded | 1961 |
| Founder | MIT developers |
| Products | Debugger software (DDT, DDT-86, DDT-68K, SDDT) |
Dynamic Debugging Technique (DDT) refers to a collection of debugger software originally designed for Digital Equipment Corporation (DEC) machines. It was initially named DEC Debugging Tape because it was distributed on paper tape. The inaugural version of DDT was developed at MIT in 1961 for the PDP-1 computer, and as it was adapted to additional systems, the original name persisted. When extended beyond DEC hardware, the designation shifted to Dynamic Debugging Tool. Early implementations of Digital Research’s CP/M and CP/M-86 incorporated the DEC-branded DDT debuggers (such as DDT-86 and DDT-68K). Eventually, the CP/M DDT was superseded by the Symbolic Instruction Debugger variants (SID, ZSID, SID86, and GEMSID) within DR DOS and the GEM environment.
Apart from its debugging role, DDT functioned as a primary command shell on MIT’s Incompatible Timesharing System (ITS). On certain ITS installations, an initial limited version called "PWORD" would run first and then be replaced by DDT after user authentication. The debugger could handle up to eight simultaneous processes ("jobs"), including nested instances of itself. Each process was assigned a distinct identifier; the main DDT session was referred to as "HACTRN." Of cultural note, Guy L. Steele composed a filk poem parodying Edgar Allan Poe’s "The Raven" entitled The HACTRN.
DEC-10/DEC-20 DDT
On the DECsystem-10 and DECSYSTEM-20, DDT supported symbolic references within debugged programs by loading symbols from the executable (.EXE) files. A specialized version called SDDT retrieved symbols directly from the active monitor, allowing system developers to examine internal system functions.
See also
- On-line Debugging Tool (ODT)
- Tracing Debugging Technique (TDT)
- DEBUG (DOS command)
- Comparison of computer shells
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 HACTRN