Dynamic debugging technique
Encyclopedia
Dynamic Debugging Technique, or DDT, was the name of several debugger
programs originally developed for DEC
hardware, initially known as DEC Debugging Tape because it was distributed on paper tape. The name is a pun on the insecticide (i.e. bug-killer) 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.
DDT is closely related to ODT
. Both names were used for several different debuggers, but generally debuggers with the ODT name had more limited capabilities than DDT debuggers.
As with other DEC tools, early CP/M
kept the DEC name DDT for its debugger. DDT was later superseded by SID.
In addition to its normal function as a debugger, DDT was also used as a top-level command shell
for the MIT
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 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"); thus Guy L. Steele's famous filk poem parody of Edgar Allan Poe
's "The Raven
," The HACTRN.
Debugger
A debugger or debugging tool is a computer program that is used to test and debug other programs . The code to be examined might alternatively be running on an instruction set simulator , a technique that allows great power in its ability to halt when specific conditions are encountered but which...
programs originally developed for DEC
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
hardware, initially known as DEC Debugging Tape because it was distributed on paper tape. The name is a pun on the insecticide (i.e. bug-killer) DDT
DDT
DDT is one of the most well-known synthetic insecticides. It is a chemical with a long, unique, and controversial history....
.
The first version of DDT was developed at MIT for the PDP-1
PDP-1
The PDP-1 was the first computer in Digital Equipment Corporation's PDP series and was first produced in 1960. It is famous for being the computer most important in the creation of hacker culture at MIT, BBN and elsewhere...
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.
DDT is closely related to ODT
Octal Debugging Technique
On-line Debugging Tool, or ODT, was the name of several debugger programs originally developed for DEC hardware. Various operating systems including OS/8, RT-11, RSX-11, and RSTS/E implemented ODT as did the firmware console of all of the LSI-11-family processors including the 11/03, 11/23/24,...
. Both names were used for several different debuggers, but generally debuggers with the ODT name had more limited capabilities than DDT debuggers.
As with other DEC tools, early CP/M
CP/M
CP/M was a mass-market operating system created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...
kept the DEC name DDT for its debugger. DDT was later superseded by SID.
In addition to its normal function as a debugger, DDT was also used as a top-level command shell
Shell (computing)
A shell is a piece of software that provides an interface for users of an operating system which provides access to the services of a kernel. However, the term is also applied very loosely to applications and may include any software that is "built around" a particular component, such as web...
for the MIT
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
ITS
Incompatible Timesharing System
ITS, the Incompatible Timesharing System , was an early, revolutionary, and influential time-sharing operating system from MIT; it was developed principally by the Artificial Intelligence Laboratory at MIT, with some help from Project MAC.In addition to being technically influential ITS, the...
operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer 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 processes
Process (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...
(called "jobs" on ITS) at a time, such as several sessions of TECO
Text Editor and Corrector
TECO is a text editor originally developed at the Massachusetts Institute of Technology in the 1960s, after which it was modified by 'just about everybody'...
, 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
Edgar Allan Poe
Edgar Allan Poe was an American author, poet, editor and literary critic, considered part of the American Romantic Movement. Best known for his tales of mystery and the macabre, Poe was one of the earliest American practitioners of the short story and is considered the inventor of the detective...
's "The Raven
The Raven
"The Raven" is a narrative poem by American writer Edgar Allan Poe, first published in January 1845. It is often noted for its musicality, stylized language, and supernatural atmosphere. It tells of a talking raven's mysterious visit to a distraught lover, tracing the man's slow descent into madness...
," The HACTRN.
External links
- DDT Command List for a freeware version written in portable CC (programming language)C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
- ITS 1.5 Reference Manual -(Artificial Intelligence Memo No. 161A)
- ITS: Luser's Guide
- The Great Quux Poem Collection -(See especially the notes to the poem The HACTRN)