DELTA (VMS)

DELTA is the name of a debugger used in the VMS operating system originally developed by Digital Equipment Corporation of Maynard, Massachusetts. DELTA is used to debug user-mode programs. It has a counterpart for debugging the operating system (the executive) itself, XDELTA.

One of DELTA's best known features is it's cryptic error-message "Eh?". This is the only error message generated by DELTA and XDELTA.