XDELTA

For the binary difference calculator, see xdelta.

XDELTA is the name of a debugger used in the VMS operating system originally developed by Digital Equipment Corporation of Maynard, Massachusetts. Unlike it's user-mode companion debugger DELTA, XDELTA is intended for debugging the operating system (the executive) itself and its related components (such as system services and device drivers) and so is capable of operating at elevated interrupt priority level.

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