Historical footnote: DDT was developed at MIT for the PDP-1 computer in 1961. At that time DDT stood for "DEC Debugging Tape". Since then, the idea of an on-line debugging program has propagated throughout the computer industry. DDT programs are now available for all DEC computers. Since media other than tape are now frequently used, the more descriptive name "Dynamic Debugging Technique" has been adopted, retaining the DDT acronym. Confusion between DDT-10 and another well-known pesticide, dichloro- diphenyl-trichloroethane (C H Cl ), should be minimal since 14 9 5 each attacks a different, and apparently mutually exclusive, class of bugs.