OpenVMS DELTA Debugger
The DELTA and XDELTA debuggers are used to monitor the execution of user programs and the OpenVMS operating system. They use the same commands and the same expressions, but they differ in how they operate. DELTA operates as an exception handler in a process context. XDELTA is invoked directly from the hardware SCB vector in a system context.
DELTA is used to debug process-context programs that execute at interrupt priority level (IPL) 0 in any processor mode. You cannot use DELTA to debug code that executes at an elevated IPL. To debug with DELTA, invoke it from within your process by specifying it as the debugger (as opposed to the symbolic debugger). XDELTA is used to debug system software executing in any processor mode or at any IPL level. Because XDELTA is not process specific, it is not invoked from a process. To debug with XDELTA, you must boot the processor with commands to include XDELTA in memory. XDELTA's existence terminates when you reboot the processor without XDELTA.